EPA903-R-98-001
CBP/TRS 193/98
Catfish Populations
in Chesapeake Bay
January 1998
Chesapeake Bay Program
EPA Report Collection
Information Resource Center
US EPA Region 3
Philadelphia, PA 19107
-------
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Main Title
Catfish populations in Chesapeake Bay
Author
Sauls, B.; Dowling, D.; Odenkirk, J.; Cosby, E.
CORP Author
Maryland Dept. of Natural Resources, Annapolis. ;Virginia Marine Resources
Commission, Newport News. VA. ;Virginia Dept. of Game and Inland Fisheries,
Richmond.;Environmental Protection Agency, Annapolis, MD. Chesapeake Bay
Program.
Publisher
printed by the U.S. Environmental Protection Agency for the Chesapeake Bay
Program,
Year Published
1998
Report Number
DBP/TRS 193/98 ; EPA 903-R-98-001; CBP/TRS-193/98
Stock Number
PB98-123235
OCLC Number
39102540
Subjects
Catfish, Chesapeake Bay, Estuaries, Surveys; Fish populations; Habitats; Freshwater
fish; Maryland; Virginia; Ictaluridae, Ameiurus catus; Ameiurus matalis; Ictalurus
punctatus, Ictalurus furcatus
Subject Added
Ent
Catfishes-Chesapeake Bay (Md. and Va.); Fish populations-Chesapeake Bay (Md.
and Va.)
Collation
58 p. : ill. ; 28 cm.
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Check with individual
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LOCATION
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PA
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Meade.MD
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Leader
This report is the result of a multi-jurisdictional effort to explore current knowledge of
the Chesapeake Bay's catfish populations. Long-term surveys of catfish species do
not exist in the Chesapeake Bay region, and basic biological data are fragmented with
small, regional studies conducted over intermittent periods of time. This report
represents a regional cooperative effort to bring together all available information and
assimilate the best possible understanding of catfish biology, ecology and stock
dynamics of native and introduced catfish species in the Chesapeake Bay system.
This report also documents the evolution of social, economic, and recreational
dependence as fisheries have developed following the naturalizaton of non-native
catfish species. As efforts shift to exploit more abundant or less regulation resources,
resilient species such as catfish should be carefully monitored. By assembling current
information and identifying research and data needs, this report establishes a
reference from which to gauge and direct future management.
"EPA 903-R-98-001." "CBP/TRS 193/98." "January 1998."
Prepared in cooperation with Virginia Marine Resources Commission, Newport News.
VA. and Virginia Dept. of Game and Inland Fisheries, Richmond. Sponsored by
Environmental Protection Agency, Annapolis, MD. Chesapeake Bay Program.
Product reproduced from digital image. Order this product from NTIS by: phone at 1-
800-553-NTIS (U.S. customers); (703)605-6000 (other countries); fax at (703)321-
8547; and email at orders@ntis.fedworld.gov. NTIS is located at 5285 Port Royal
Road, Springfield, VA, 22161, USA.
Sauls, Beverly.
United States. Environmental Protection Agency. Chesapeake Bay Program.
Annapolis :
1998.
PC A05/MF A01
LIBRARY Date Modified
EJA 19980522
EJD 19990313
m
19990312111337
OCLC/T
eng
OCLC
MERGE
01030nam 2200265Ka 45020
http://cave.epa.gov/cgi/nph-bwcgis/BASIS/ncat/pub/ncat/DDW?W%3DTITLE+PH+WOR... 8/17/2006
-------
Catfish Populations in
Chesapeake Bay
Prepared by
Beverly Sauls
Maryland Department of Natural Resources
David Dowling and John Odenkirk
Virginia Department of Game and Inland Fisheries
Ellen Cosby
Virginia Marine Resources Commission
for the
Fishery Management Plan Workgroup
Living Resources Subcommittee
Chesapeake Bay Program
Annapolis, MD
Printed by the U,S. Environmental Protection Agency
for the Chesapeake Bay Program
-------
TABLE OF CONTENTS
PURPOSE . . . / 1
BIOLOGY
Introduction 1
Species Identification 2
Historical Ranges, Local Distribution, and Abundance 3
Range 3
Distribution and Abundance in the Chesapeake Bay System
1. Susquehanna River, Pennsylvania to Conowingo Dam 4
2. Upper Bay, Susquehanna Flats to Magothy River 6
3. Mid-Bay Transition Zone and Tributaries, Magothy River to Potomac River 7
4. Lower Bay, Potomac River to James River 10
Habitat Requirements 10
Reproduction and Development 12
Growth and Maturity 14
Maryland Stock Assessment Data 17
Feeding Strategies 19
Nonindigenous Aquatic Species 20
Ecological Role 20
Ecological and Economic Impact 21
Policy and Recommendations 22
Habitat Alterations 22
Obstructions to Fish Migration 22
Flow and Hydrographic Alterations 23
Water Quality 23
Toxic Contaminants 24
Suspended Sediments 24
Dissolved Oxygen 24
Riparian Forest Buffers 24
Chesapeake Bay Program Habitat Restoration and Protection Efforts 25
Water Quality 25
Fish Passage , 25
FISHERIES
Commercial Fisheries 26
Market Considerations 28
Recreational Fishery 28
Management 30
Laws and Regulations 30
Fishery Mangement Plan (FMP) Development 30
RESEARCH AND DATA NEEDS
Commercial Data Needs 39
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Recreational Data Needs 39
Research Needs 40
Impacts of Non-native Catfish Introductions 40
Habitat Alteration 41
LITERATURE CITED 42
APPENDK A. Laws and Regulations 52
Maryland 52
Virginia 54
Potomac River 55
Washington, D.C 55
Pennsylvania 56
APPENDDC B. Catfish Workgroup 57
APPENDDC C. Glossary of Terms 58
TABLES AND FIGURES
Table 1: Historic abundance of white and channel catfish in the Susquehanna Flats
from MDNR trawl surveys 6
Table 2: Abundance of white and channel catfish in MDNR trawl surveys in the
Choptank River 7
Table 3: Biological survey of the anadromous and resident fishes of the Potomac and
Anacostia Rivers within the District of Columbia 8
Table 4: Comparisons of reported mean length and weight at capture of blue catfish
at age 16
Table 5: Mean length at age or length range at age for Flathead Catfish 17
Table 6: Bullhead landings and dockside value from Virginia voluntary reports 27
Figure 1: Catfish distribution in the Chesapeake Bay system by zone 5
Figure 2: Channel catfish and white catfish captured at the Conowingo Dam
fish lift facility 31
Figure 3: Brown bullheads and yellow bullheads captured at the Conowingo Dam
fish lift facility 32
Figure 4: Catfish indices from Maryland and Chesapeake Bay juvenile striped bass
seine survey 33
Figure 5: Virginia trawl survey catfish indices 34
Figure 6: Estimated average daily streamflow into Chesapeake Bay 35
Figure 7: Maryland commercial catfish landings and dockside values 36
Figure 8: Virginia commercial catfish landings and dockside values 37
Figure 9: Potomac River commercial catfish harvest landed in Maryland and Virginia . 38
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PURPOSE
This report is the result of a multi-jurisdictional effort to explore current knowledge of the
Chesapeake Bay's catfish populations. Long-term surveys of catfish species do not exist in the
Chesapeake Bay region, and basic biological data are fragmented with small, regional studies
conducted over intermittent periods of time. This report represents a regional cooperative effort
to bring together all available information and assimilate the best possible understanding of catfish
biology, ecology and stock dynamics of native and introduced catfish species in the Chesapeake
Bay system. This report also documents the evolution of social, economic, and recreational
dependence as fisheries have developed following the naturalization of non-native catfish species.
As efforts shift to exploit more abundant or less regulated resources, resilient species such as
catfish should be carefully monitored. By assembling current information and identifying research
and data needs, this report establishes a reference from which to gauge and direct future _
management.
BIOLOGY
Introduction
North American catfish from the family Ictaluridae are freshwater species that commonly
range into estuarine waters. Large members of the genus Ictalurus (forktail catfishes) are
important commercial, recreational and aquacultural species. Medium-size species from the genus
Ameiurus (bullheads) are important recreational species and are moderately exploited
commercially. Madtoms, small catfish of the genus Noturus, are found primarily in high reaches of
freshwater creeks and small rivers and are not covered in this report.
Three species of bullheads are native to the Chesapeake Bay system: white catfish
(Ameiurus catus1), brown bullhead (A. nebulosus1), and yellow bullhead (A. natalis3). Two
introduced species of catfish, channel catfish (Ictalurus punctatus) and blue catfish (7. furcatus),
have become economically important to the region. Channel catfish are established in the upper
Bay and tributaries throughout the Bay system. Blue catfish, once considered rare, are becoming
increasingly abundant in several drainage systems. A third introduced species, flathead catfish
(Pylodictis olivaris), has only a limited distribution in Chesapeake Bay at present. Habitats are not
clearly partitioned between species, and overlap is common. When found together, one species
usually dominates, as has been observed with white and channel catfish in the Choptank River
(Bonzek and Morin 1988) and Virginia tributaries (VIMS unpublished data) and with blue and
channel catfish in the upper reaches of some Virginia tributaries (VDGEF unpublished data).
1 Previously known as Ictalurus catus.
~ Previously known as Ictalurus nebulosus
3 Previously known as Ictalurus natalis
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Channel Catfish
Blue Catfish
COLOR:
FINS:
OTHER:
COLOR:
FINS:
OTHER:
Gray to greenish-gray or yellow-olive,
sides fade to silver-gray, white belly.
Juveniles have black speckles.
Caudal fin deeply forked, 24 - 29 anal
rays.
Barbels extend past head, upper jaw
slightly protruded.
Pale blue to white underneath.
Caudal fin deeply forked. Anal fin
straight-edged with 30-36 anal rays.
Steeply sloping predorsal profile, heavy
bodied. Largest Bay species.
White Catfish
COLOR: Bluish-gray on back and sides, white
underneath.
FINS: Caudal fin moderately forked, 19-23
anal rays.
OTHER: Noticeably broad head and stout body.
Smaller than blue and channel cats.
Brown Bullhead
COLOR: Brown back, sides often mottled brown,
white underside.
FINS: Square, slightly notched caudal fin. 20 -
24 anal rays.
OTHER: Dark barbels, serrated pectoral spine.
Yellow Bullhead
COLOR: Light olive to dark brown, yellow sides,
white underside.
FINS: Rounded caudal fin, 24 - 27 anal rays.
OTHER: Yellow to white barbels, short bodied.
-------
Flathead Catfish
COLOR: Olive to dark brown with dark
marbled blotches. Yellow to
olive underneath.
FINS: Squarish, white-edged tail.
14-17 anal rays (rarely 13 or
18 rays).
OTHER: Broad, flat head. Lower jaw
protrudes beyond upper jaw.
Historical Ranges, Local Distribution, and Abundance
Range
White catfish, brown bullhead, and yellow bullhead inhabit fresh and brackish water bodies
of central and eastern North America. White catfish are an eastern species that occur along the
Atlantic and Gulf Coast States from New York to Florida. Brown bullheads range from Maine to
Florida and from the Great Lakes in the Midwest south to Texas. Yellow bullheads range from
Connecticut to Florida and the Gulf States and north to Minnesota in the central United States.
The native range of channel catfish extends from southern Canada, through the Great
Lakes and central United States drainage system, to Mexico including all the Gulf States and
some of the Atlantic Coast. Extensive introductions have resulted in a current range that
encompasses essentially all of the Pacific and Atlantic drainage systems in the 48 continental states
(Lee et al. 1980; McMahon and Terrell 1982). According to Jenkins and Burkhead (1994),
channel catfish from Missouri and Illinois were first stocked in the Potomac River during 1889-
1905 and into the Upper James River during 1893-1894. Channel catfish have been so successful
in the Chesapeake Bay drainage system that they are now believed to be the most abundant
Ictalurus species in the upper Bay (MDNR unpublished data).
Blue catfish range north into Canada and south through eastern Mexico with large
populations in the lower Mississippi and Missouri rivers. The species was indigenous to
Pennsylvania in the Ohio River drainage system, but has been extirpated. The range of blue catfish
in the United States has been extended from California to the east coast through stocking. Blue
catfish numbers are steadily increasing in Chesapeake Bay tributaries as the result of intentional
stocking, most notably in Virginia (VDGEF unpublished data). Young fish from a Texas hatchery
were introduced in the mid 1970's by the Virginia Department of Game and Inland Fisheries
(VDGIF) into Virginia waters. Records indicate that a total of 97,800 fish were introduced in the
Rappahannock in 1974, 1975, and 1977; 64,100 in the James in 1975 (Jenkins and Burkhead
1994). The Mattaponi River (a tributary of the York River) was stocked with 1,850 blue catfish in
1985 (VDGEF unpublished data). The origin of blue catfish in the Potomac River is not well
documented.
Flathead catfish are native to the southern Great Lakes and Mississippi basins and most
Gulf slope drainage systems. It has been introduced on the Atlantic slope and in California. In
Virginia, flathead catfish are indigenous to the New, Tennessee, and Big Sandy drainage systems,
and introduced to the Chesapeake Bay system in the Potomac, James and Roanoke drainage
-------
systems (Jenkins and Burkhead 1994). The establishment of the flathead catfish on the Atlantic
slope in Virginia stemmed from releases of apparently few individuals, as also reported in the
Cape Fear River, North Carolina (Guier et al. 1984). Introductions to the lower James and middle
Roanoke rivers, including Smith Mountain Reservoir, via accidental and intentional releases
during 1965-1977, are discussed by Burkhead (1980). The flathead catfish is expected to spread
throughout the James and Roanoke rivers (Jenkins and Burkhead 1994). Although it is classed as
only semi-mobile by Funk (1955), it dispersed rapidly and widely in the Cape Fear River, North
Carolina, following establishment (Guier et al. 1984).
Distribution and Abundance in the Chesapeake Bay System
There are four general zones of catfish distribution in the Chesapeake Bay system (Figure
1). Zone 1, the Susquehanna River, is entirely freshwater. Zone 2, the upper Chesapeake Bay,
contains low salinities that allow catfish to freely migrate between the Bay mainstem and adjacent
river systems below dams. Salinity barriers to migration fluctuate seasonally and annually in Zone
3, the mid-Bay, and catfish distribution down-river and in the Bay mainstem is limited. In Zone 4,
the lower Bay, catfish are restricted to rivers and tributaries and migration between adjacent rivers
does not occur.
Zone 1. Susquehanna River, Pennsylvania to Conowingo Dam
Open water is defined in this document as a body of water that migratory fish can freely
enter and exit. The Susquehanna River is obstructed by the Conowingo Dam, which is currently
operated to provide hydroelectric power. The dam has been in place since 1928. In 1991, a fish
lift operation was implemented at the Conowingo Dam to transport anadromous fish, particularly
Alosa species (shad and herring), to spawning habitat upriver. Catfish species present in 1996 at
the fish lift, in order of decreasing abundance, were channel catfish, white catfish, brown bullhead,
and yellow bullhead (SRAFRC 1997). Blue catfish are not present in the Susquehanna River.
Currently, catfish caught at the fish lift are examined and returned to waters below the
Conowingo Dam; however, some catfish may pass the dam and move upriver through a partially
automated system on the east shore which transports all species over the dam into Conowingo
Lake. Fish passage facilities at three dams upriver from Conowingo Dam are currently under
design and construction. Upon completion, all fish lift operations at Conowingo Dam will become
automated and will not select for targeted species.
Data on catfish species collected at the Conowingo Dam fish lift since 1973 show a
decline in channel catfish, white catfish (Figure 2) and bullheads (Figure 3). The reason for this
decline is unknown, particularly in light of their high abundance in the Susquehanna Flats and
Upper Bay, and no formal investigation of this decline has been conducted. One speculation is the
decline may be due to the introduction of gizzard shad (Dorosoma cepedianuni) to above-darn
impoundments in 1972. Gizzard shad are plankton feeders and the transfer of energy to this non-
native species following its introduction is believed to be the cause for declines in the black
crappie (Pomoxis nigromaculatus) population noted by 1976 in Conowingo Pond. Catfish
production above the dam may be similarly affected and subsequent recruitment of juvenile catfish
from Conowingo Pond to tailwaters below the dam may have also declined as a result
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Zone 1: Susquehanna River. Closed system
above Conowingo Dam up through
Pennsylvania; open system below Conowingo
Dam to Zone 2.
Zone 2: Susquehanna Flats to Magothy River.
Open system, no salinity barriers to migration.
Mainstem Salinity (average, 1949-1994):
Susquehanna Flats to Aberdeen Proving Grounds: 1.3
ppt
Aberdeen to Severn River 5.9 ppt
Zone 3: Magothy River to Potomac River.
Semi-open system, migration between rivers
possible during periods of high rainfall and low
salinity.
Mainstem Salinity (average, 1949-1994):
Severn River to Chesapeake Beach: 10.3 ppt
Chesapeake Beach to Patuxent River 12.1 ppt
Patuxent River to Potomac River 13.6 ppt
Zone 4: Lower Bay, Potomac River to James
River.
Closed river systems; migrations restricted by
salinity barrier in lower portions of major rivers.
Average salinity at the Potomac River mouth can be as
low as 10 ppt during years of high rainfall (1949-1994
data).
Figure 1. Catfish distribution in
the Chesapeake Bay system
by zone.
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(Chris Frese, SRAFRC, personal communication). Other speculations may be recreational fishing
pressure at the Conowingo Dam, commercial fishing pressure downstream, or some
environmental alteration that has affected important catfish habitat.
Above the Conowingo Dam, catfish species present throughout the Susquehanna system
in Pennsylvania include, in order of decreasing abundance: brown bullhead, channel catfish, and
yellow bullhead (Richard Snyder, PFBC, personal communication). The introduced channel
catfish are highly sought after by recreational anglers. Stocks are often sustained as put-and-take,
with the most recent stocking of channel catfish occurring in 1993. The only known flathead
catfish specimen from Pennsylvania's portion of the Chesapeake Bay system was captured from a
lake in Lancaster County and returned.
Zone 2. Upper Bay, Susquehanna Flats to Magothy River
Field studies in 1927 documented only white catfish in the upper Bay (Hildebrand and
Schroeder 1972 reprint). Presence of channel catfish at the Susquehanna River mouth is noted as
early as 1961, though they were uncommon in other parts of the state (Schwartz 1961). Channel
catfish were first introduced to the Susquehanna River system in impoundments. From there, they
were stocked in impoundments across Maryland and, in some cases, directly into open waters for
the purpose of providing a recreational fishery (Leon Fewlass, MDNR, personal communication).
Channel catfish are highly abundant in the upper Bay and are now considered a naturalized species
throughout Chesapeake Bay. Naturalized species are defined as introduced species which are
established and have been self-sustaining for at least 10 years (CBP 1993).
Beach seine surveys conducted by Maryland's Department of Natural Resources (MDNR)
in the Susquehanna Flats document channel catfish presence since 1958 (MDNR unpublished
data, 1958-1995; Figure 4). Trawl surveys offer a better measure of juvenile abundance for catfish
due to their habitat preferences. In 1968 and 1969, a trawl survey was conducted in the
Susquehanna Flats and catfish densities were calculated (Table 1). The study was repeated in
1980 and 1981 and channel catfish abundance increased nearly three-fold. Channel catfish is now
the dominant Ictalurus species in the upper Bay.
Table 1. Historic abundance of white and channel catfish and brown bullhead in the Susquehanna
Flats from MDNR trawl surveys (Carter 1973; Weinrich et al. 1981, 1982).
YEAR SAMPLE AREA
1968/69 Susquehanna Flats (118.5 acres)
1980 Susquehanna Flats (65.6 acres)
1981 Susquehanna Flats (60.1 acres)
# CATFISH PER ACRE
CHANNEL
4.0
12.6
10.5
WHITE
<1.0
0
0.2
BROWN
BULLHEAD
0.5
1.0
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Zone 3. Mid-Bay Transition Zone and Tributaries, Magothy River to Potomac
River
The upper Bay is an open system where freshwater conditions allow catfish to move freely
throughout. Salinity conditions in the mid-Bay are dependent on levels of annual precipitation,
which varies seasonally, and may restrict movement of catfish between adjacent tributaries.
Winter snow melt and spring rainfall influence freshwater input from upper tributaries and, as
precipitation tapers off during summer months, salinities generally rise. Commercial landings in
the Bay mainstem from 1975 to 1993 suggest catfish are not as abundant in the Bay mainstem
below the Magothy River as they are in the upper Bay. Average landings in the upper Bay
mainstem are approximately 145,000 pounds annually; whereas, average landings in the mainstem
south of the Magothy River to the Potomac River are only about 1,500 pounds per year (MDNR,
unpublished data, 1975-1993).
Channel catfish were introduced into the Potomac River system near Hagerstown in
western Maryland from 1889 to 1892 by the U.S. Fish Commission. In 1929, channel catfish were
documented in the upper Potomac River system around Montgomery County, MD (Truitt et al.
1929). Beach seine surveys conducted by MDNR in the Potomac, Choptank and Nanticoke rivers
since 1956 document channel catfish presence. In the tidal Potomac River, channel catfish were
present in beach seines below Pomonkey Creek in 1957, though their numbers were very low.
Between 1957 and 1977, their frequency in seine samples gradually increased. Channel catfish are
reported to be the second most abundant species in jurisdictional waters of Washington, DC
(Table 3). Channel catfish were not collected in seine surveys in the Choptank River until 1978
and in the Nanticoke River until 1979.
In addition to seine survey results, trawl surveys in the Choptank River in 1971 and 1972
found no channel catfish. In 1986 and 1987 and again in 1993 and 1994, channel catfish were not
only present, but had become more abundant than the native white catfish during the intervening
15 years (Table 2).
Table 2. Abundance of white and channel catfish from MDNR trawl surveys in the Choptank
River (MDNR unpublished data 1971-1987; MDNR unpublished data collected from Casey et al.
1988; Piavis etal. 1995).
YEAR
1971/72
1986
1987
1993
1994
AREA
Choptank River (summer)
Choptank River (spring)
Choptank River (spring)
Choptank River (spring)
Choptank River (spring)
# CATFISH PER ACRE
CHANNEL
0
36.0
46.5
14.9
213.0
WHITE
8.0 -
6.4
17.9
4.0
67.0
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In 1988, Bonzek and Morin (1988) reported approximately a 2:1 ratio of channel catfish
to white catfish from both fyke nets and trawl surveys in the Choptank River. Piavis et al. (1994),
reported increased ratios during 1994, to almost 3:1 channel catfish to white catfish from fyke
nets and 4.5:1 from trawl surveys. Trawl surveys from both studies collected small fish; whereas,
fyke nets captured larger, mature fish.
Channel catfish and, to a lesser extent, white catfish were unusually abundant in the Bay
mainstem south of the Magothy River during 1994. The years 1993 and 1994 experienced greater
precipitation than normal and Susquehanna River flows were the highest since Hurricane Agnes in
1972 (Bay Journal 1994a). Salinities in the upper to mid-Bay during the spring of these years
were highly diluted. Rains in 1994 persisted through the summer months and held salinity at
freshwater levels through July (Bay Journal 1994b). In the Patuxent River, Kendall and Schwartz
(1968) noted that downstream dispersal of white catfish was limited by salinity and suggested that
this species may migrate to stay within a particular salinity regime. The influx of channel and
white catfish to lower Bay stations may be the result of favorable salinities during 1993 and 1994
which allowed catfish to extend their foraging range.
Catfish in the Potomac River are most abundant above 52 miles (32 km) from the river
entrance (Lippson et al. 1979). This same river mile is the approximate boundary between
oligohaline (0.5-5.0 ppt salinity) and mesohaline (5.0-18.0 ppt salinity) conditions in the Potomac
River mainstem. Biological surveys during 1973 and 1974 from 63 miles (39 km) upriver to 80.4
miles (26 km) upriver ranked all species encountered in order of abundance. Brown bullheads
ranked fourth, white catfish were ninth, channel catfish were thirteenth, and blue catfish were not
present (EAI 1974). More recent surveys in the jurisdictional waters of Washington, DC,
recorded five species of catfish (Tilak and Siemien 1993; 1994; 1995; 1996; 1997). The native
brown bullhead was the dominant species, followed by the non-native channel catfish (Table 3).
Yellow bullhead and white catfish naturally occur in District waters, though their abundance was
very low. In addition, the non-native blue 'catfish was reported to be present in low numbers
(Table 3).
Table 3. Biological survey of anadromous and resident fishes of the Potomac and Anacostia
Rivers within the District of Columbia (Tilak and Siemien 1991; 1992; 1993; 1994; 1995; 1996;
1997). Number of catfish sampled.
Brown Bullhead
Channel Catfish
Yellow Bullhead
White Catfish
Blue Catfish
1990
212
217
14
6
0
1991
295
83
2
1
0
1992
418
120
6
8
5
1993
1474
73
1
1
2
1994
876
121
11
6
2
1995
462
69
2
7
3
1996
281
133
0
8
2
Length Range
3 8-3 87mm
42-700mm
12-330mm
274-856mm
260-700 mm
-------
Blue catfish have been documented in the Potomac River, which is currently the most
northern tributary in which this species ranges in Chesapeake Bay. Blue catfish may have been
stocked in the Potomac River near Washington, DC, between 1898 and 1905, though the
accuracy of records documenting their introduction has been questioned (Burkhead et al. 1980).
Burkhead et al. (1980) revisited historically documented blue catfish specimens from the Potomac
River and, in some instances, found them to be misidentified channel catfish. Nammack and
Fulton (1987) captured a blue catfish at the mouth of the Anacostia River in 1987, and speculated
on the origin of the specimen. Possible sources for introduction of blue catfish to the open waters
of the Potomac River included Burke and Brittle lakes in Virginia, which were stocked with blue
catfish and may have allowed for escapes during high water conditions; the adjacent
Rappahannock River by recreational fishermen; or via Chesapeake Bay during a year of reduced
salinity.
Since Nammack and Fulton documented their presence in 1987, records of blue catfish in
the Potomac River have continued to be random and sporadic, though a few sightings have been
consistently reported since 1992. Biological surveys in the Washington, DC, portion of the
Potomac and Anacostia Rivers since 1990 reported no blue catfish until 1992 (Table 3; Tilak and
Siemien 1993; 1994; 1995; 1996; 1997). In 1994, the juvenile striped bass seine survey in
Maryland captured one blue catfish young-of-year in the Potomac River approximately 73.5 miles
(45.6 km) upriver (Don Cosden, MDNR, personal communication). Otherwise, there has been no
evidence of reproduction by blue catfish in the Potomac River basin. Pennsylvania reports no blue
catfish in the upper portion of the Potomac River system (Richard Snyder, PFBC, personal
communication).
Another introduced species to the Potomac River drainage system is the flathead catfish.
Apparently, a few (<15) flathead catfish were stocked in the Occoquan Reservoir in Virginia in
1965 and are now established in open waters of the Occoquan River, a tributary of the Potomac
River (Jenkins and Burkhead 1994). Flathead catfish were also reported in Potomac River and
stocked in Lake Brittle, Virginia. Truitt et al. (1929) reported a large catfish species, then
recorded as Ameiurusponderosus, commonly called the Mississippi catfish, in the Potomac River
between Chain Bridge and Georgetown. The species was reportedly introduced by the U.S.
Bureau of Fisheries and was described as large, up to 32 pounds, with a long head and a caudal
fin not deeply forked. Whether this was an attempt to introduce flathead catfish or another
unidentified species is unknown. Since no such species has been collected in biological surveys of
Washington, DC, it appears to have been unsuccessful.
The appearance of blue and flathead catfish in Potomac River may pose the threat of
expansion into adjacent tributaries and the upper Bay. Salinity in the mid-Bay region adjacent to
the Potomac River entrance may be low enough during abnormal events, such as a hurricane, to
allow blue catfish to exit the river and expand into the Upper Bay. Larger than both white or
channel catfish, blue catfish may represent serious competition to related Ictalurid species and
other native species. Flathead catfish also grow to large sizes and could compete with the existing
Ictalurid stocks if the species were to expand in abundance and distribution in the Chesapeake
Bay system. The establishment of flathead catfish in Virginia stemmed from releases of apparently
few individuals. Similar releases of a small number of individuals in the Cape Fear River in North
Carolina also resulted in successful introduction (Guier et al. 1984).
-------
Zone 4. Lower Bay, South of Potomac River to James River
Salinity in the lower portions of tributaries of the lower Bay exceeds the upper tolerance
limits of catfish species and inhibits movement between adjacent rivers. Trawl surveys conducted
by the Virginia Institute of Marine Science (VIMS) in the lower Chesapeake Bay and tributaries
did not find catfish outside of tributaries (VIMS unpublished data, 1983-1993). In the lower 35
miles (22 km) of the James, York, and Rappahanock Rivers, the greatest overall catfish
abundance occurrs at upriver stations. White catfish is the dominant species and channel catfish is
the second most abundant (Figure 5). Lanier (1971) reported the greatest abundance of catfish in
the James River between 40 and 70 miles (25 to 43 km) upriver during 1969 and 1970 and did not
report the presence of blue catfish. In VIMS trawl surveys conducted since 1983, blue catfish
have been collected primarily in the upper portions of the sample area. Increased trawl survey
indices for blue catfish since 1990 are believed to be the result of an upriver, five mile expansion
in survey area (Figure 5; Bonzek et al. 1995); however, increasing frequencies of blue catfish
captured in lower river stations during this same time period suggest the species may be
expanding its distribution as densities increase upriver (Patrick Geer, VIMS, personal
communication).
Surveys conducted by VDGIF 176 miles (109 km) up the Rappahannock River
documented a substantial blue catfish population in 1991. In 1993 and 1994, large numbers of
blue catfish were collected adjacent to the bridge pilings of the Benjamin Harrison Memorial
Bridge in the James River by VDGEF. Additionally, blue catfish were collected by VDGIF from
Herring Creek in the James drainage system, from Occupacia Creek and Gingoteaque Creek in the
Rappahannock drainage system, and during 1994 in the tidal portion of the Chickahominy River
(James'River drainage). Citations awarded to anglers for record fish in recent years show an
increasing number of large fish, weighing up to 66.5 pounds (VDGEF unpublished data).
Although Ictalurids are tolerant of estuarine conditions, upstream portions of major rivers
and estuaries where salinities are highly diluted or diminished appears to be the preferred habitat
of channel catfish and blue catfish. This observation is based on trawl surveys in major rivers in
Virginia (Patrick Geer, VIMS, personal communication) and the dominant status of channel
catfish in the headwaters of Chesapeake Bay. In a Louisiana estuary with a salinity range of 0.18
ppt to 35.0 ppt, blue catfish were collected in waters up to 11.4 ppt salinity (Perry 1969). Given
their tolerance for moderate salinities, blue catfish presence in lower portions of tributaries may be
expected as populations become more established.
Habitat Requirements
Much of the information available on habitat requirements for catfish pertains to
freshwater habitats. Little information exists on Ictalurids in estuarine environments. As a result,
this section should not be considered complete for catfish populations throughout their range in
the Chesapeake Bay system.
10
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Temperature
Catfish are warm water species that tolerate cold temperatures for overwintering. Catfish
are relatively heat-tolerant (Kendall and Schwartz 1968). White catfish acclimated at 20°C can
tolerate temperatures between 29°C and 31°C (Kendall and Schwartz 1968). The upper heat
tolerance of brown bullheads is 29.1°C to 35.3°C, and channel catfish acclimated at 20°C can
tolerate up to 32.7°C (Hart 1952).
Salinity
Catfish of the family Ictaluridae, while considered freshwater species, are common
downstream into the brackish waters of the Chesapeake Bay mainstem to Kent Island, Maryland,
where salinities range up to 10 ppt (Lippson and Lippson 1984).
Brown bullheads suffer stress in salinities above 10 ppt (cited in Jones et al. 1978). Yellow
bullheads have been observed in 15 ppt salinity (Kilby 1955); however, the species is not beleived
a common estuarine inhabitant (Jenkins and Burkhead 1994). Kendall and Schwartz (1968)
reported a lethal salinity for white catfish of 14 ppt (LC50, 60 hours); however, the species was
reported in salinities as high as 15 ppt in the Potomac River (Lippson et al. 1979).
Channel catfish were reported in salinities as high as 15 ppt in Potomac River (Lippson et
al. 1979). Tagging studies by Dames et al. (1989) suggest large adult channel catfish leave
backwaters and reside in river areas where they become largely piscivorous. Blue catfish, though
tolerant of salinities up to 11.4 ppt (Jenkins and Burkhead 1994), have not been observed in the
lower portions of Bay tributaries and it is not believed that they have ventured too far into
estuarine waters. In a Louisiana estuary with a salinity range of 0.18 ppt to 35.0 ppt, blue catfish
were collected in waters up to 11.4 ppt salinity (Perry 1969).
Dissolved Oxygen
Catfish are relatively resistant to low dissolved oxygen levels. Jones et al. (1988) reported
habitat requirements for channel catfish, white catfish and brown bullheads. The level of dissolved
oxygen required for growth and successful reproduction was 5.0 ppm, although the species can
apparently tolerate dissolved oxygen levels as low as 3.0 ppm. Lethal dissolved oxygen
concentrations for channel catfish at 25°C, 30°C, and 35°C were 0.76 ppm, 0.89 ppm and 0.96
ppm, respectively (Jones et al. 1978).
Physical Habitat
The yellow bullhead prefers shallow fresh water with dense vegetation and are often
associated with cover (Jenkins and Burkhead 1994). Trautman (1981) cited loss of submerged
vegetated habitat in two Ohio lakes as the cause for yellow bullhead decline. Trautman (1981)
also cited competition from brown bullheads as a cause for depressed yellow bullhead
populations. The yellow bullhead is tolerant of high acidity and is the most abundant species in the
Dismal Swamp, Virginia (Jenkins and Burkhead 1994).
The brown bullhead is found over muddy bottoms, is known to burrow into soft
sediments, and is sometimes associated with vegetation (Jones et al. 1978). The brown bullhead
may be found in stagnant water, but is usually restricted to deep canals in sluggish rivers,
11
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sometimes in dense schools (Jones et al. 1978). Habitat preferences sometimes overlap with white
catfish in shallow, silty slow-flowing tributaries as well as open, clear and deep water.
White catfish typically avoid dense vegetation and are found in slow-moving streams, river
backwaters, reservoirs and ponds. White catfish prefer less current than channel or blue catfish
and are more tolerant of silty bottoms (Sternberg 1987). Trautman (1981) observed that white
catfish habitat preferences fall in between those of brown bullheads, which prefer quiet waters and
silted bottom, and channel catfish, which prefer more current and hard bottom. In large river
systems of Chesapeake Bay, white catfish more frequently occupy down-river stations; whereas,
channel catfish and blue catfish abundance dominate upriver (VIMS unpublished data). White
catfish are rarely found in small streams (Jenkins and Burkhead 1994).
Channel catfish prefer deep-channeled rivers, streams, and brackish estuaries with slow to
moderate current. The species is frequently associated with pools and is adapted to clear and
turbid waters, but is apparently not tolerant of acidic conditions (Jenkins and Burkead 1994).
Channel catfish prefer sand, gravel or rubble bottoms (Sternberg 1987) and easily adapt to
enclosed water bodies of lakes, reservoirs and ponds.
The blue catfish is a large-river species which typically inhabits deep, swift-flowing
channels and pools (Jenkins and Burkhead 1994). They prefer clearer, swifter water than other
catfish and are associated with unsilted bottoms of sand, gravel, or rock (Sternberg 1987; Etnier
and Starnes 1993). Trautman (1981) stated that feeding was done in the swift-flowing chutes or
rapids and over bars, or elsewhere in pools, where there was good current and solid substrates.
The Ohio River population reportedly declined when the river was ponded in 1911, which
reduced flow and created a deep silted bottom (Trautman 1981). When not feeding and during
winter months, they apparently retreat into deeper water and enter sloughs and backwaters in
spring (Jenkins and Burkhead 1994).
The flathead catfish inhabits large, warm-water streams, rivers, lakes and reservoirs and
favors deep pools with little flow (Jenkins and Burkhead 1994). Flatheads are tolerant of heavy
turbidity, though they are usually associated with hard or slightly silty bottoms (Trautman 1981)
scoured by currents, such as those adjacent to bridge pilings, and in tailraces below dams
(Manooch and Raver 1991). During daylight hours, adults are strongly associated with cover such
as caves, undercut banks, brush piles, and logjams (Minckley and Deacon 1959).
Reproduction and Development4
Catfish species move upstream to spawn in freshwater during late spring and early summer
when water temperatures reach 21-27°C. Their use of estuarine waters for spawning is unknown.
White catfish
White catfish spawn in still or flowing waters near sand or gravel banks. Large, saucer-
shaped nests are formed by both male and female fanning their sides and fins on the bottom.
Approximately 1,000 to 4,000 adhesive eggs are laid. Males guard the nest and undulate their
4 For review and citations, see Jenkins and Burkhead 1994; Jones et al. 1978; Mansueti and Hardy 1967.
12
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bodies to aerate eggs and disturb sediments on the egg surfaces. Both brown bullheads and white
catfish were observed sucking eggs into their oral cavity and forcefully shooting them back out
into the nest, which may also remove sediments and debri. Males may remain close to the nest
after hatching until the fry break from schooling tendencies and disperse. Yolk-sac larvae are 9.0-
9.8 mm total length (TL; 0.36-0.4 inches) at hatch and are tadpole-like juveniles at approximately
14.0 mm (0.56 inches).
Bullheads
Brown bullheads may spawn up to twice a year in late spring. Nesting sites are in shallow
water of slow-moving tributaries. Nests may be excavated in sand or mud, often under logs, brush
or banks or any other available cover, and in vegetation on firm substrate such as sand, gravel or
stone. Eggs are adhesive. Small females lay approximately 2,000 eggs; whereas, larger females
may lay up to 13,000 eggs and may reproduce several times during a season. Nests may be
guarded by one or both of the parents and are aerated and kept free of sediments. Eggs hatch in
five to eight days at water temperatures of 20 to 24°C. Parents may remain near the nest after
hatching, and fry stay in the nest six to eight days. Juveniles prefer low salinities of 1.7 ppt or less
with a maximum tolerance of 11 ppt. The optimum dissolved oxygen level for growth is 7 ppm or
greater. Yellow bullheads lay between 1,650 and 7,000 eggs in shallow, saucer-shaped nests in
shallow water, usually beneath a bank, log or tree root. Juveniles are 17-21 mm TL (0.68-0.84
inches).
Channel catfish
Channel catfish usually spawn once a year, in the summer, and lay approximately 2,000 to
21,000 eggs in turbid tributaries, sometimes in areas of swift current. Two spawning peaks per
season is not uncommon. Spawning typically occurs between the hours of 1230 am - 0730 am and
0330 pm - 0530 pm (Jones et al. 1978). Channel catfish select nest sites in dark depressions,
cavities, or undercut stream banks, or inside crevices, hollow logs, or man-made containers.
Spawning success is dependent on available cover (Marzolf 1957). Spawning usually occurs in
salinities of 2 ppt or less. Upon hatching, sac-fry of channel catfish are tolerant of salinities up to 8
ppt and 9-10 ppt following yolk absorption; however, growth and survival through the fingerling
stage is best in fresh water up to 5 ppt (Allen 1971). Channel catfish fry sometimes aggregate in
tight schools after leaving the nest until suitable cover is found. Fingerlings shelter or aggregate
during daylight hours and disperse and feed at night (Brown et al. 1970). The upper lethal
temperature is approximately 37°C with abnormal development at 35°C (Jones et al. 1978).
Blue catfish
Blue catfish spawning occurs in spring, beginning as early as April in Louisiana and
extends into June farther north (Etnier and Starnes 1993). On 24 June, 1994, a 29.9 kg (66
pounds 8 ounces) gravid female, the Virginia state record blue catfish, was caught in the
Appomattox River near its confluence with the James River. Preferred spawning temperatures
range from 21° C to 24° C (Jenkins and Burkhead 1994). Manooch and Raver (1991) indicated
that blue catfish eggs are deposited in nests constructed under logs, brush, or the riverbank.
Because blue and channel catfish spawn at the same time and temperature, as well as select similar
13
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nest sites (Jenkins and Burkhead 1994), interspecific competition for spawning substrate may
occur.
Flathead catfish
Flathead catfish spawn June through August, in shallow waters with temperatures from
22° C to 29° C. Nests are usually associated with submerged logs or protected areas along river
banks. Eggs are adhesive and fecundity varies with female size. Small fish may lay 4,000 eggs;
larger fish may lay up to 93,000 (Manooch 1984). Males guard the nest, and after hatching, young
and juvenile flathead catfish are usually associated with riffles in streams (Jenkins and Burkhead
1994).
Growth and Maturity
The five species of catfish and bullheads grow and mature at different rates. Growth may
also occur at different rates for different sexes of the same species. Blue catfish and flatheads are
the largest species in Chesapeake Bay, followed by channel catfish. White catfish and brown and
yellow bullheads do not grow to enormous sizes. Channel catfish and white catfish grow at the
same rate during their first year. After the first year, channel catfish continue to increase in length
and weight and white catfish continue to accumulate weight without increasing much in length
(Menzel 1943; Lanier 1971; Bonzeck and Morin 1988). Ramsey and Graham (1991) cited several
investigators who documented that blue catfish grow more rapidly and live longer than channel
catfish.
White catfish
White catfish mature at three to four years of age (Manooch 1984). A study in the
Patuxent River found fish from this age group to be 170-220 mm (6.8-8.8 inches) TL (Schwartz
and Jackowski 1965). This is comparable to a more recent Choptank River study (Bonzek and
Morin 1988) and another study in the James River (Lanier 1971). Longevity of white catfish,
based on one large specimen from Higgins Millpond in Dorchester County, MD, was estimated to
be 14 years (Schwartz and Jackowski 1965).
Bullheads
Brown bullheads grow up to 18 inches (450 mm) and 3-4 pounds (1.4-1.8 kg). This
species is estimated to reach maturity at three years or older (Manooch 1984) and may live to. ten
years or more.
Channel catfish
Channel catfish size and age at maturity varies between sexes and among locations. Male
channel catfish in the Susquehanna River ranged from 6 to 23 mm (0.2-0.9 inches) larger than
females (Fewlass 1980). In a southwest Louisianna study, female channel catfish grew slower than
males and matured at a larger size and older age (Perry and Carver 1972). In Louisiana, Perry
and Carver (1972) found 100% of females 350-359 mm (14-14.4 inches) in length were mature
and 100% of males 330-339 mm (13.2-13.56 inches) were mature. Female channel catfish
14
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examined in Susquehanna River matured as early as three years of age at 200 to 250 mm (8-10
inches) total length (Fewlass 1980). Fish in this study were thought to have slow growth rates due
to the dense population of channel catfish in the study area; however, other studies in Choptank
River (Bonzek and Morin 1988) and James River (Menzel 1942; Lanier 1971) found only slightly
greater lengths at age. Studies in Potomac River (Sanderson 1958; Bonzek and Morin 1987)
found substantially greater lengths at age than in the James, Susquehanna, and Choptank River
studies illustrating variability in growth within the Bay. This variability may also be affected by
selective fishing pressure or river-specific primary productivity, rather than interspecific
competition due to overcrowding. Longevity of channel catfish was documented as 24 years in
Canada (Scott and Grossman 1973).
Blue catfish
Blue catfish are reported to grow to 68 kg (150 pounds), however, the largest specimen to
date from the Chesapeake Bay system was 30.2 kg (66.5 pounds; VDGJJ state record). Blue
catfish show no significant difference in growth rates between sexes (Brooks et al. 1982);
however, females mature at a larger size and older age (Perry and Carver 1972). Limited studies
were done on age and growth of blue catfish within the Chesapeake Bay drainage system. Table
4 indicates the mean length and weight at capture of blue catfish, age 0-10, in James River at
Hopewell, VA, which were captured on 17 September, 1993, by VDGIF. Length at age in the
James River compared favorably with values shown by Stemberg (1987) and Manooch and Raver
(1991) for other aquatic systems in the United States (Table 4). Jenkins and Burkhead (1994)
reported the weight at maturation of cultured fish was approximately 2.3 kg (5.1 pounds), which
Carlander (1969) indicated would be about 400-600 mm (16-24 inches) TL. Age and growth
were figured for blue and channel catfish in southeast Louisiana by Perry and Carver (1972). One-
hundred percent of female blue catfish, estimated to be five years and older and greater than 590
mm (23.6 inches) long, were mature. Four-year-old males 490 mm (19.6 inches) and longer were
also mature. These lengths were considerably larger than mature channel catfish in the same study
(100% maturity: females, 350-359 mm (14-14.4 inches); males 330-339 mm (13.2-13.6 inches).
Longevity of blue catfish is recorded to 21 years (Pflieger 1975).
15
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Table 4. Comparisons of reported mean length and weight at capture of blue catfish at various
ages.
Age
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
N
1
18
23
10
22
6
2
0
1
0
2
0
0
0
0
James River at Hopewell, VAS
Mean length
mm (inches)
112.5(4.5)
207.5 (8.3)
290.0(11.6)
385.0(15.4)
455.0(18.2)
555.0 (22.2)
680.0 (27.2)
-
632.5 (25.3)
-
832.5 (33.3)
-
-
-
-
S.D.
-
21.0
29.7
39.2
66.6
40.8
72.0
-
-
-
8.0
-
-
-
-
Mean weight
g (pounds)
9.0 (0.02)
74.6(0.16)
198.4 (0.44)
552.4(1.22)
1044.2 (2.30)
2333.3(5.14)
4625.0 (10.20)
-
3130.0(6.9)
-
8390.0(18.50)
-
-
-
-
S.D.
-
24.2
55.8
188.0
599.0
906.0
1675.0
-
-
-
240.0
-
-
-
-
Southeast, U.S.6
Mean length
mm (inches)
-
147.5 (5.9)
265.0(10.6)
360.0 (14.4)
452.5(18.1)
537.5 (21.5)
620.0 (24.8)
650.0 (26.0)
682.5 (27.3)
807.5 (32.3)
872.5 (34.9)
947.5 (37.9)
970.0 (38.8)
1025.0(41.0)
1050.0(42.01
North America7
Mean length
mm (inches)
-
155.0(6.2)
277.5(11.1)
367.5 (14.7)
457.5(18.3)
552.5(22.1)
637.5 (25.5)
720.0 (28.8)
765.0 (30.6)
807.5 (32.3)
852.5(34.1)
-
-
-
-
5 Data collected on September 17, 1993, by VDGIF. Data from Virginia Commonwealth University, 1994.
6 Reported by Manooch and Raver (1991).
7 Reported by Sternberg (1987).
16
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Flathead catfish
Flathead catfish mature at about three years of age and as small as 380 mm (15.2 inches;
Etnier and Starnes 1993). They are known to grow to 1400 mm (56 inches) and 45.4 kg (100
pounds). Age and growth data are given in Table 5.
Table 5. Mean length at age or length range at age for Flathead Catfish.
AGE
1
2
3
4
5
6
7
8
9
11
13
15
Sternberg 1987
North, U.S.
mm (inches)
187.5(7.5)
272.5 (10.9)
370.0(14.8)
-
482.5 (19.3)
-
597.5(23.9)
-
700.0 (28.0)
887.5 (35.5)
925.0 (37.0)
1000.0 (40.0)
South, U.S.
mm (inches)
-
407.5 (16.3)
607.5 (24.3)
-
692.5 (27.7)
-
867.5 (34.7)
-
907.5 (36.3)
1010.0(40.4)
1105.0(44.2)
1157.5(46.3)
Manooch and
Raver 1991
Southeast, U.S.
mm (inches)
60.0 (2.4)
115.0(4.6)
195.0 (7.8)
305.0(12.2)
442.5 (17.7)
542.5 (21.7)
605.0 (24.2)
647.5 (25.9)
682.5 (27.3)
757.5 (30.3)
807.5 (32.3)
-
Etnier and Starnes 1993
Tennessee
mm (inches)
62.5-235.0(2.5- 9.4)
125.0-352.5(5.0- 14.1)
182.5-467.5(7.3- 18.7)
255.0-570.0(10.2-22.8)
315.0-637.5(12.6-25.5)
370.0-767.5(14.8-30.7)
415.0-892.5(16.6-35.7)
457.5-970.0(18.3-388)
-
-
-
-
Maryland Stock Assessment Data
Rothschild et al. (1992) estimated mortality rates for white catfish and channel catfish in
Maryland's Chesapeake Bay. White catfish mortality was based on a small sample of 44 fish; total
instantaneous mortality (Z) was 0.51; Z for channel catfish was 0.67. More accurate estimates of
mortality from larger sample sizes are currently being generated from data collected by the
Maryland Department of Natural Resources (Jim Uphoff, MDNR, personal communication).
In 1993, Maryland initiated a comprehensive sampling of resident and migrant Chesapeake
Bay recreational finfish (COMPFISH). The COMPFISH project is a multispecies survey which
monitors adult resident and ocean migrant species during the spring, summer and fall. Spring
sampling targets catfish populations. Length frequency and age data are collected for both channel
17
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catfish and white catfish in the Upper Bay and Choptank, Chester, and Nanticoke Rivers. The
following results are summarized from Piavis et al. (1994; 1995), Markham and Piavis (1996),
and Markham et al. (1997).
Choptank River
Catfish were collected from five experimental fyke nets set in the Choptank River between
65 and 78 km (40-48 miles) upriver from the mouth. The nets were fished March through May.
Experimental trawls, which sampled age 0 catfish more adequately, were discontinued in 1995.
Trawl data from 1993 and 1994 are presented in Table 2. The mean length for channel catfish
between 1993 and 1996 did not show a significant trend and ranged between 389 mm ±113 (15.6
inches ±4.5) and 451 mm ±132 (18.0 inches ±5.28). In 1996, nine year classes of channel catfish
were observed between the ages of two and ten years old. In 1995, only seven year classes were
observed (two to eight years old). The presence of age two channel catfish increased between
1995 and 1996. Instantaneous mortality (Z) was estimated in 1996 to equal 0.15. The relationship
of Z and growth rate (K) for channel catfish in Choptank River was estimated. Relative mortality
(Z/K; Z = instantaneous mortality rate; K = Brody growth coefficient) was 0.24 in 1995 and 0.60
in 1996. The appearance of a strong 1994 year class during 1996 indicated that recruitment has
not been impacted by harvest pressure in the near term.
White catfish are not a highly targeted species for exploitation and competitive interaction
among channel catfish may have more of an impact on this species than the recreational and
commercial harvest. Relative mortality rates for white catfish were 2.6 in 1995 and 0.6 in 1996.
The mean length for white catfish from 1993 to 1996 ranged between 269 mm ±89 (10.8 inches
±3.6) and 327 mm ±83 (13.1 inches ±3.3) and did not show a significant trend.
Nanticoke River
Nanticoke River catfish were sampled during 1995 and 1996 from four commercial pound
nets between 23 and 37 km (14 to 23 miles) upriver from the mouth. The nets were sampled from
late February to early May. The mean length of channel catfish from Nanticoke River was 399
mm ±90 (16.0 inches ±3.6) in 1995 and 427 mm ±72 (17.1 inches ±2.9) in 1996. The age
structure of catfish from the Nanticoke River was compared with the Choptank River. Overall,
channel catfish from the Nanticoke River were younger. However, the percentage of young
channel catfish between the ages of two and four years declined from 1995 to 1996 in the
Nanticoke River (46% to 15%) while age two fish increased in the Choptank River (1% to 13%).
Estimates of relative mortality in the Nanticoke River were similar during 1995 and 1996
(numbers not reported) and total mortality for 1996 was estimated to be 0.3.
The mean length of white catfish in the Nanticoke River was 264 mm ±103 (10.6 inches
±4.1) in 1995 and 267 mm ±89 (10.7 inches ±3.6) in 1996. Relative mortality rates for white
catfish were 1.3 in 1995 and 4.4 in 1996.
Chester River
Catfish were collected from five commercial pound nets in the Chester River between 30
and 32 km (19-20 miles) upriver from the mouth. The nets were sampled April through May. The
mean length for channel catfish has been increasing every year since 1993; however, confidence
18
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intervals overlap between years and between the lowest and highest values and the increase is not
significant (range 423 mm ±86 to 485 mm ±72; 16.9 inches ±3.4 to 19.4 inches ±2.9). Total
mortality for channel catfish was 0.2 in 1996, and relative mortality rates declined from 1.1 in
1995 to 0.78 in 1996.
White catfish mean lengths were between 303 mm ±58 (12.1 inches ±2.3) and 383 ±55
(15.3 inches ±2.2) from 1993 to 1996 and showed no significant trend. The relative mortality rate
increased from 0.6 in 1995 to 0.8 in 1996.
Upper Bay
Commercial pound nets in the upper Chesapeake Bay mainstem were sampled for catfish
during October. Mean lengths for channel catfish in the upper Bay were between 416 mm ±74
(16.6 inches ±3.0) and 493 mm ±47 (19.7 inches ±1.9) between 1993 and 1996. Relative
mortality estimates were 0.31 in 1995 and 0.82 in 1996. Total mortality for channel catfish during
1996 was estimated to be 0.2. White catfish are rarely encountered in the upper Bay and no data
was given for the species.
Feeding Strategies
Catfish are opportunistic feeders with highly varied diets. Common food categories are
aquatic plants and seeds, fish, molluscs, insects and their larvae and crustaceans. Brown bullheads
and white catfish examined from the Potomac River were found to be full of herring eggs (Weiser
1969). A study of stomach contents of channel catfish from the Susquehanna River found small
amounts of bryozoans, arachnids, gastropods and nematodes (Fewlass 1980). Channel catfish
typically seek cover during the day and move from deep, sheltered areas to shallow areas at night
to feed (Pflieger 1971; Brown et al. 1970). Flathead catfish exhibit the same diurnal behavior
(Trautman 1981).
Habitat partitioning occurs between adults and young due to food preference. Subadults
and adults leave backwaters and shift from invertebrates to a mainly piscivorous diet (Jones et al.
1978). Fewlass (1980) found evidence of food partitioning between different aged channel catfish
in the Susquehanna River. Young-of-year fed mainly on crustaceans and insects. Fish age one and
older consumed significantly less crustaceans and more insects, and catfish 250 mm and greater
(>10 inches) fed more frequently on small fish. Perry (1969) found similar partitioning of food
between size classes for channel and blue catfish in brackish waters in Louisiana. Blue catfish 95-
187 mm long (3.8-7.5 inches) fed mainly on small invertebrates, with fish appearing in catfish
100-240 mm (4.0-9.6 inches). Catfish greater than 200 mm (8.0 inches) fed primarily on fish and
macroinvertebrates including blue crab (Callinectes sapidus). Flathead catfish are more
piscivorous than blue and channel catfishes and are known to eat gizzard shad, freshwater drum,
carp, channel catfish, bullheads, bluegill, and crayfish (Manooch 1984). Juvenile flatheads feed
more on insects and crustaceans.
Although catfish and bullheads have poor eyesight, their barbels are well-equipped with
taste buds which help them find food at night and in muddy waters (Sternberg 1987). According
to Atema et al. (1969) and Todd (1971), the olfactory apparatus is responsible for recognizing
19
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other individuals and their social status, while barbels and other dermal taste buds are the
structures used for locating food.
Nonindigenous Aquatic Species
Ecological Role
No studies exist that qualify possible factors which led to the success of nonindigenous
introductions of Ictalurid species in Chesapeake Bay. Such success is dependent on the
physiological, behavioral, and ecological potential of the new species, as well as the physical and
biological properties of the ecosystem receiving the introduction (Taylor et al. 1984). Successful
introductions, as reviewed by Taylor et al. (1984), are often species which posess physiological
tolerances, feeding habits, or reproductive capabilities that differ from native species and function
as a selective advantage. Catfish are nocturnal, opportunistic feeders, and their ability to find food
in dark, murky waters through chemosensory detection may offer some advantage over local
species. Physiological aspects, such as tolerance for polluted and degraded conditions and wide
salinity ranges, may also be selective advantages.
Habitat alterations prior to introductions also increase the chances for survival of non-
native species (Courtenay and Williams 1992). Native species that are stressed due to habitat
alteration, fishing pressure, or a combination of both often experience population decline.
Courtenay et al. (1986) suggested that introduced species probably act synergistically with
anthropgenic changes and are able to fill niches previously occupied by native species. For
example, brown bullheads were introduced into Europe in the 1880s to stock heavily
industrialized rivers that contained few fish. Kendall (1902) recognized the ablility of catfish to fill
vacant niches when he saw little objection to the introduction of bullheads into waters unsuited to
other fishes or in which fishes did not live.
Declines in sensitive native fish species, which may compete with introduced species for
food or habitat, may have contributed to the successful introduction of non-native catfish species
in the Chesapeake Bay system. Sensitive species are fhose with vulnerable life history stages that
are not highly tolerant of natural or anthropogenic changes in environmental conditions. Jordan et
al. (1990) compared Chesapeake Bay species with sensitive early life stages (i.e. anadromous and
semi-anadromous fish that spawn in freshwater reaches), with more tolerant and persistent
species. Persistent species such as mummichog (Fundulus heteroclitus) and Atlantic menhaden
(Brevoortia tyrannus) functioned as opportunistic species, and the authors suggested they may fill
niches vacated by sensitive species due to degraded water quality and/or overfishing.
Anthropogenic sources for sensitive species declines include loss of spawning habitat,
deteriorating water quality (particularly in spawning reaches), and fishing pressure (Vaas and
Jordan 1990).
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The increasing range and abundance of catfish in the upper Bay may be temporary and the
result of unusually wet years during 1993 and 1994 (Figure 6). Catfish may be exploiting new
foraging areas during wet seasons and retreating to more suitable habitat during dry seasons.
However, changes in the Chesapeake Bay system may be contributing to a more permanent
expansion of catfish in the upper Bay mainstem. Forest cover in the Chesapeake Bay watershed
has been reduced from 95% to less than 60% since colonial settlement; wetlands have been
reduced by about 50% (27% of original wetlands remain in Maryland, 58% in Virginia, 44% in
Pennsylvania). Vegetative cover is important for regulating stream flow and moderating salinity
after storms and during wet seasons. In devegetated areas or that have been covered with
impervious surface, rain washes over land and directly drains into waterways over a short period
of time and in greater quantities, causing salinities downstream to rapidly fluctuate. The result is
greatly reduced salinities after storms and during wet seasons. It has been estimated that peak
freshwater flows to the Bay before development and agriculture in the watershed were 25 to 30%
less than they are today (Biggs 1981). As growth in the watershed continues and forest cover is
lost, the ability of the watershed to moderate salinity during wet seasons is expected to decrease.
As a result, reduced salinities during spring and early summer may provide greater opportunity for
catfish to forage over an expanded area and possibly invade new tributaries. The effects of
increased catfish distribution in Chesapeake Bay is largely undocumented and the effects of their
presence on community structure are unknown.
Ecological and Economic Impacts
Known and potential impacts from the introduction of non-native fishes in U.S waters
were reviewed by Taylor et al. (1984) and include habitat and trophic alterations by the
introduced species, hybridization with native species, and spatial alterations. The escape or
introduction of aquaculture species to open waters have had negative effects on native fauna,
habitat and regional economies in the past, as reviewed by Courtenay and Williams (1992). For
example, Mozambique tilapia was introduced on an international scale and is now considered a
pest species due to its high fecundity and ability to displace native fishes (Bardach et al. 1972;
Ling 1977; Shelton and Smitherman 1984). Courtenay and Williams (1992) reported that in nearly
every case where an exotic aquatic species has been the subject of culture, escape into open
waters occurred. Shelton and Smitherman (1984) noted the escape of exotic species is virtually
inevitable and such eventuality should not be overlooked. Welcomme (1988) went further to say
any introduction for aquaculture should be considered as a potential addition to the wild fauna.
Blue catfish are a highly prized recreational fish in Virginia with trophy potential. A
commercial market has also evolved around the emerging resource. However, expansion and"
establishment of blue catfish and flathead catfish north of the Potomac River could have negative
economic impacts. Maryland's commercial fishery caters primarily to the live catfish market and
targets channel catfish because they adapt well to confinement. Conversations with commercial
harvesters reveal blue catfish do not adapt as easily to confinement, are difficult to bring to market
live and in good condition, and may also damage other marketable fish contained within fishing
gear (Appendix B).
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Policy and Recommendations
Maryland law prohibits the introduction of nonindigenous fish species* without first
obtaining a permit that certifies the specific fish to be imported is free of disease and will not be
harmful to native flora and fauna. Permits may be obtained for aquaculture of nonindigenous fish
in Maryland, as long as the activity does not adversely affect wild stocks offish; result in the
release of non-native species into Maryland waters, except in confined water such as ponds where
there are safeguards to prevent escape; or result in the contamination of native or naturalized
species offish or their ecosystem.
The Chesapeake Bay Policy for Non-Indigenous Aquatic Species (CBP 1993) requires
that each jurisdiction list species that are considered native or naturalized within their waters.
Species not listed will be subject to management as laid out in the Policy. The Introduction of
Non-Indigenous Aquatic Species Implementation Plan (CBP 1996) addresses five issues:
aquaculture (private and public), research, monitoring, education, and control. It focused on the
following aspects of unintentional introduction of nonindigenous aquatic species: 1) identification
of introduction pathways; 2) risk assessment for the respective pathways; 3) development of
appropriate protocols to minimize the risks associated with unintentional introduction; and 4)
education as a means of preventing unintentional introduction.
With the exception of one juvenile blue catfish collected in 1994, there is no evidence that
blue catfish are potentially reproducing in the Potomac River system. It is recommended that blue
catfish not be considered as native or naturalized in the Potomac River system or within
Maryland, Pennsylvania or Washington, DC, jurisdictional waters and subject to management as
laid out in the Chesapeake Bay Policy for Non-Indigenous Aquatic Species. Flathead catfish
should also be excluded from the list of native or naturalized species in Maryland; Pennsylvannia;
Washington, DC; and isolated river systems of Virginia where they have not been introduced or
become established.
Habitat Alterations
Obstructions to Fish Migration
More than 1,000 miles of migratory fish spawning habitat are currently blocked by dams
and other obstructions in the Chesapeake Bay system (Chesapeake Executive Council 1993). The
effects of habitat alteration above and below stream and river blockages have been documented
for catfish species. Trautman (1981) indicated that the ponding of the Ohio River and the
subsequent rapid and deep silting above the dams destroyed preferred blue catfish habitat.
Catfish are commonly concentrated below dams, possibly due to migratory blockage
during spawning (Trautman 1957; Pflieger 1975; Richards et al. 1986). Walburg (1971) proposed
a combination of food availability, suitable temperatures and currents, activities related to
spawning and the presence of a dam that prevented further upstream movement as the cause for
channel catfish concentrations below the Lewis and Clark Lake in South Dakota. Below
Conowingo Dam, injured gizzard shad that pass through the turbines attract a number of species
Nonindigenous fish pertains to species hot native and species not self-sustaining, or naturalized, in Maryland
waters for at least ten years.
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to feed. Tailwaters below impoundments with hypolimnal (bottom water) release are
characterized by reduced water temperatures, hard substrate and reduced biodiversity; such
environments are unsuitable catfish habitat (Hagen and Roberts 1973). Epilimnetic (surface water)
releases are less disruptive; tailwaters are of moderate temperatures, well oxygenated, and heavy
metals are generally not present.
Catfish in impoundments are self-sustaining, but stocking is common to supplement
recreational fishing. For management purposes, catfish above migratory obstructions are treated
as closed populations, though there is some passage over dams or through intakes. Mortality
associated with catfish entrained in turbines or passed over dams is unqualified in Chesapeake
Bay. Although catfish are not target species for fish passage programs, they may benefit from the
removal of stream blockages and the construction offish passages. Use offish ladders by catfish
has been documented in Maryland. A channel catfish was found by the Maryland Fish Passage
Program in the Bloede Dam Fishway of the Patapsco River (Larry Leasner, MDNR, personal
communication). The Bloede Dam Fishway is a Denil design and measures 293 linear feet (89 m)
with a vertical height of 25 feet (7.6 m). Brown bullhead were also documented using a smaller
Denil fishway (87 feet linear length, 4.7 feet vertical height; 26.5 m linear length, 1.4 m vertical
height) in Tuckahoe Creek, a tributary of the Choptank River (Larry Leasner, MDNR, personal
communication). Migratory fish passages may facilitate the expansion of blue catfish, particularly
in the upper Bay where reduced salinity allows for exploration of adjacent tributaries.
Flow and Hydrographic Alterations
High velocity water flows below impoundments scour soft and fine-grained bottom
sediments and expose hard substrate. Spawning habitat is reduced, and nests are frequently
washed out during high flow events in these areas. Channel catfish populations have been
eliminated below dams with cold bottom-water (hypolimnal) discharge, but concentrate in
tailwaters with warm surface-water (epilimnetic) discharges. Catfish may also be attracted to
tailwaters where food-fish spil over dams.
Loss of vegetation over large portions of a watershed may increase streamflow and hinder
reproductive success of native Ictalurids. Vegetated riparian buffers moderate streamflow after
storms and moderate variance in flow between wet and dry seasons (CBP 1995). White catfish
prefer still or flowing waters, and brown bullheads prefer slow moving tributaries. Channel catfish
are known to spawn in swift current and may not be affected by increased streamflow.
Water Quality
Freshwater Withdrawal
Catfish populations in Chesapeake Bay are concentrated in fresh and low salinity portions
of rivers and the upper Bay mainstem. Salinity barriers which restrict catfish distribution fluctuate
yearly, based on precipitation patterns in the watershed. Freshwater withdrawals above the fall
line for present and future human use could move salinity barriers upstream and restrict catfish
distribution to a smaller area.
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Toxic Contaminants
Catfish are bottom feeders and are resident species of Chesapeake Bay throughout their
entire life history; these factors cause catfish to be susceptible to bioaccumulation of
contaminants. Some studies conclude Ictalurid species are tolerant of various contaminants
(Bauman et al. 1987; Roberts and Bendl 1982). Brown bullheads taken from an industrialized
Lake Erie tributary exhibited high frequencies of liver tumors and external tumors (Bauman et al.
1987). Toxins accumulated in brown bullhead tissue included organic contaminants and
carcinogenic polyaromatic hydrocarbons (PAHs). High levels of tissue contamination in areas of
Back River (Baltimore Harbor), Elizabeth River (Norfolk, VA), and a section of the Potomac
River near Washington, D.C., have resulted in closure to catfish harvest. During 1990-1993,
Virginia issued warnings for channel and flathead catfish in the upper James River due to
contamination by dioxin, a byproduct of the bleaching of paper pulp.
The accumulation of kepone is related to residence time and distance from the source of
contamination (Bender et al. 1977). Channel catfish and white catfish retain relatively low levels
of kepone, compared with largemouth bass (Bender et al. 1977), eel, and bluegill (Roberts and
Bendl 1982). Channel catfish fingerlings exposed to kepone under laboratory conditions
experienced highest accumulations in blood and brain tissue (Van Veld 1980). White catfish in the
same experiment experienced highest accumulations in blood and liver tissue. When kepone was
removed from the diet, channel catfish were able to begin eliminating the pesticide from their
bodies, and the half life was 8.7 days (Van Veld 1980). Roberts and Bendl (1982) calculated an
96-hour LC50 for channel catfish exposed to kepone equal to 514 micrograms per liter.
Kaumeyer and Setzler-Hamilton (1982) summarized toxicity of selected pollutants to
white catfish, brown bullheads, and channel catfish including metals, pesticides, polychlorinated
biphenyls (PCBs), halogenated compounds and monocyclic aromatic hydrocarbons. Results and
parameters of laboratory studies on tolerance limits of catfish to various chemical compounds
were summarized and include acute toxicity and chronic or sublethal toxicity.
Suspended Sediments
See Riparian Forest Buffers, below.
Dissolved Oxygen
See Habitat Requirements section titled Dissolved Oxygen on page 11.
Riparian Forest Buffers
Riparian areas with forest cover provide logs, branches and other submerged cover for
protected nest sites, as well as overhead cover during spawning and egg development. Nest sites
of brown bullheads, channel catfish, blue catfish, and flathead catfish are often associated with
cover, and woody debris may be an important habitat for nesting and hatching success.
Loss of vegetative cover, particularly riparian buffers, in a surrounding watershed
increases turbidity in connected water bodies. Survival of young catfish during their first year is
greatest in turbid water (Lawler 1960; Pflieger 1975). However, Marzolf (1957) reported an
absence of reproduction by channel catfish in turbid waters where overhead cover was lacking.
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This suggests that loss of riparian buffers may reduce the area available for channel catfish
reproduction.
Chesapeake Bay Program Habitat Restoration and Protection Efforts
Water Quality
In the 1987 Chesapeake Bay Agreement (Chesapeake Executive Council 1987),
Chesapeake Bay Program partners set a goal to reduce the nutrients nitrogen and phosphorus
entering the Bay by 40% by the year 2000. In the 1992 Amendments to the Chesapeake Bay
Agreement (Chesapeake Executive Council 1992), partners agreed to maintain the 40% goal
beyond the year 2000 and to attack nutrients at their sourceupstream in the tributaries. Nutrient
reduction will increase the survival of benthic species, stimulate species diversity and reduce
anoxia in bottom waters.
In 1994, the Executive Council of the Chesapeake Bay Program adopted the Chesapeake
Bay Basinwide Toxics Reduction and Prevention Strategy (CBP 1994). The goal of the toxics
strategy is, "a Chesapeake Bay free of toxics by reducing or eliminating the input of chemical
contaminants from all controllable sources to levels that result in no toxic or bioaccumulative
impact on the living resources that inhabit the Bay or on human health." The strategy
commitments go beyond point-source control and begin to address the more difficult tasks of
controlling stormwater runoff and atmospheric deposition. Implementation of efforts to identify
the origin of nonpoint source toxics will be used to develop strategies to reduce contaminants
from those sources in the future. ,
Fish Passage
The Bay Program is committed to opening blockages in the tributaries for passage of
anadromous fish to freshwater spawning grounds. Fish passage goals established in 1993 direct
Bay Program signatories to open 582 stream miles by 1998 and over 1,356 miles by 2003
(Chesapeake Executive Council 1993). As of September 30, 1997, a total of 392 miles have been
opened.
The Conowingo Dam on the Susquehanna River was fitted with a new fish lift in 1991. In
1997, Maryland opened the last remaining barrier on Patapsco River's mainstem, Simpkins Dam.
Pennsylvania completed fish lifts at Safe Harbor and Holtwood Dams on the Susquehanna River
(the largest lifts of this kind in the nation) and a fish passage at Rock Hill Dam, on the Conestoga
River. Virginia began construction on a fish passage at Boshers Dam in Richmond, a project "that
will open 138 miles on the mainstem of the upper James River. Catfish are not a target species for
fish passage programs in Chesapeake Bay and it is not known if they will benefit as a result. There
is some concern that fish passages may be utilized by blue or flathead catfish should they expand
their range into the upper Bay.
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FISHERIES
Commercial Fisheries
Species of current commercial importance include channel catfish in Maryland, Virginia,
and Potomac River, and blue catfish in Virginia river systems where they are most abundant.
Brown bullheads support a small specialized market and yellow bullheads are not commercially
targeted but may be mixed in as by-catch with other catfish species.
Several gears are employed for commercial catfish harvest in Chesapeake Bay. Traditional
pound nets catch large quantities of catfish in the upper Bay region and tributaries are
characterized by different combinations of gears used by local harvesters in each region. Gears
used to commercially harvest catfish include baited fish pots, fyke nets, haul seines, and pound
nets. Trotlines with baited hooks are set in Virginia and were commonly used in Maryland before
multiple-hooked lines were prohibited.
Maryland
Hildebrand and Schroeder (1972 reprint) investigated Maryland's catfish fishery in 1929,
prior to channel catfish introductions. During that period, primarily white catfish were
commercially harvested with hook and line, pound nets, and fyke nets, and the species was an
important market fish in Baltimore and Washington, D.C. Today, the major portion of the market
is for channel catfish (Sauls 1997 and Appendix B). Total Maryland landings in 1996 were 1.99
million pounds. Landings were reported by species for the first time in 1996: channel catfish
comprised 1,116,586 pounds, white catfish comprised 85,413 pounds, and 740,752 pounds were
reported as unknown (MDNR unpublished data 1996). Records since 1975 indicate an increasing
trend in commercial catfish harvest (Figure 7), probably due to the increasing availability as
channel catfish have become more abundant and markets have developed. Since 1986, landings
have averaged 1.55 million pounds and, more recently, landings from 1994 to 1996 averaged
close to 2 million pounds (MDNR unpublished data 1996). Next to menhaden, catfish landings
rank second in weight of all commercial finfish species harvested in the state.
The principal market for wild catfish harvested from Maryland is for live fish, which are
purchased to stock private ponds for paid sportfishing (Sauls 1997 and Appendix B). Trautman
(1981) reported the shipment of "many tons" of white catfish from Maryland and Virginia, over a
15 year span prior to the early 1980s, to stock sportfishing ponds. White catfish were said to be
desirable because of their size and easy catchability. As the channel catfish population increased to
a size that could support commercial harvest, live fisheries have evolved since the 1980s to target
the more desirable channel catfish. Live harvest from Chesapeake Bay supplies catfish buyers in
several midwest states (EL, IN) and eastern mountain states (OH, WV, PA; Sauls 1997 and
Appendix B). Market demand is for fish which exceed the minimum size limit of 10". Harvesters
report approximately 90% of the market is for fish 15" and greater with the exception of 10-12"
for the fingerling market (Appendix B). The threatened presence of blue catfish in Maryland could
have negative economic impacts on commercial harvesters that sell to the live market.
Commercial harvesters from Chesapeake Bay report that blue catfish do not adapt well to
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confinement, are easily damaged when contained in gear and live wells, and large blue catfish
damage other marketable fish held in nets and traps (Appendix B).
Virginia
Menzel (1943) investigated the early commercial catfish fishery in the James and Potomac
Rivers. In general, the average fisherman and fishery biologist were relatively unfamiliar with this
"small but locally important" catfish industry. Catfish landings in 1940 ranked only 13th in
quantity from harvest in Virginia. Menzel reported catch composition, which included channel
catfish and white catfish with an average weight of 1 pound, and brown and yellow bullheads
which averaged !/2 pound. Six Virginia fishermen from the Potomac, James, and Rappahannock
Rivers interviewed in 1994 reported the optimum desired weight for catfish was eight pounds and
was regulated by market demands. Fish less than or greater than approximately eight pounds were
not desirable and were reportedly thrown back.
Since Menzel's (1943) early investigation, blue catfish have become a significant species in
the commercial harvest and channel catfish continue to be in high demand. The principal market for
blue catfish is for food and the live
markets for channel catfish do not seem to
be as established in Virginia as they are in
Maryland. Harvest of white catfish may no
longer be significant due to changes in
market preference (Appendix B).
Since 1975, commercial catfish
landings in Virginia averaged 916,000
pounds per year (Figure 8). More recently,
landings from 1994 to 1996 averaged
758,000 pounds. Bullhead harvest in
Virginia may be voluntarily reported as
such or included in catfish landings.
Bullheads support only local markets or
are taken as bycatch and are believed to
make up only a small portion of the commercial harvest. Reported landings for bullheads in Virginia
are given in Table 6 and are also included in totals for Figure 8.
Potomac River
Fisheries in the Potomac River below the District of Columbia, and not including
tributaries in Maryland or Virginia jurisdictions, are regulated by the Potomac River Fisheries
Commission (PRFC). Species-specific size limits are in effect in PRFC jurisdictional waters. Size
limits for channel catfish and white catfish take into account the different growth rates and are 8"
and 10" respectively. Bullheads must be a minimum size of 6".
Catfish landings since 1964 in the Potomac River ranged from 400,141 pounds to only
6,252 pounds (Figure 9). Average landings from 1964 to 1995 were approximately 190,000
pounds per year (PRFC unpublished data, 1964-1995). Bullhead landings are reported separate
from catfish in the Potomac River and ranged from 0 to 104,880 pounds since 1982 (PRFC
Table 6. Bullhead landings and dockside value in
Virginia from voluntary reports (VMRC
unpublished data 1993-1996).
Year
1993
1994
1995
1996
Pounds
43,750
103,550
23,614
98,290
Dockside Value
$ 7,333
$15,972
$ 4,488
$18,676
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unpublished data, 1982-1995). Blue catfish are not abundant enough to support a commercial
fishery and channel catfish comprise the majority of commercial harvest. Brown bullheads support
a small portion of commercial harvest, with yellow bullheads taken as bycatch. Commercial
fishing is not permitted in the District of Columbia.
Commercial landings were analyzed in four zones of the Potomac River by Lippson et al.
(1979). In the 26.4 river miles (16.4 km) of the upper-most zone, beginning 76 miles (47.1 km)
from the river entrance to the jurisdictional boundary of Washington, DC, catfish landings were
the highest of all species harvested during the years 1964-1971. During that same time period,
nearly 90% of catfish harvest in the Potomac River was from that zone (Lippson et al. 1979).
Market Considerations
Of the five Ictalurid species available in the Chesapeake Bay region, only two support
significant markets. Channel catfish are harvested for the food market and also sold live to stock
fishing ponds. Blue catfish are desirable in the food market for their white filets that are attractive
for display and are preferred by some buyers because they are easily skinned by machine. White
catfish yield less meat per fish and are not as marketable; however, a local market in Maryland
reports that once customers try white catfish they prefer the flavor over channel catfish. Brown
bullheads yield red filets and support a small, specialized market. Yellow bullheads are not
commercially targeted but may be mixed in catfish harvest as bycatch.
Commercial harvesters in the Chesapeake Bay region are concerned that the market for
wild catfish for human consumption has suffered from competition with farm raised catfish. The
largest aquaculture operations for catfish occur in southeastern states, most notably Louisianna
and Alabama. The aquaculture industry provides a product of consistent quality and availability,
and wild catfish often cannot compete with farm-raised catfish in the food market. Channel catfish
are the primary species for farming and can be raised in outdoor ponds to market size in about 18
to 24 months. Indoors, in controlled conditions, catfish feed consistently and grow faster.
Aquaculture is a relatively new industry in Maryland. Eight catfish growout operations and
nine fee fishing ponds were registered in the state in 1995. In 1991, 161,820 pounds of catfish
were cultured in Maryland, and increased to 236,853 pounds in 1992. Extreme winter
temperatures in 1993 are suspected of causing the 74% decline in Maryland catfish production
which was only 61,800 pounds. The 1994 estimate increased to 197,350 pounds (MDA 1995).
Brachyplatysoma vaillanti, a wild catfish from Brazil, are also imported to the United
States. The imported product is less expensive than domestic farm raised products and is a
competitive product in the food market.
Recreational Fishery
The acceptance of catfish as a sportfish is documented in the 1991 U.S. Fish and Wildlife
Service Fishing and Hunting Survey (U. S. Department of Interior 1993). Nationally, catfish rank
third in angler preference (U. S. Department of Interior 1989). Recreational catfish harvest in
Chesapeake Bay is estimated by an angler survey, the Marine Recreational Finfish Sportfishing
Survey (MRFSS), conducted by the National Marine Fisheries Service (NMFS). Catfish harvest
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may be underestimated for Chesapeake Bay as a result of survey design, which does not sample
the upper tidal freshwater portions of rivers where a high level of recreational catfish angling
occurs (Piavis et al. 1994). Catfish anglers in the Chesapeake Bay region are diverse and range
from charter boat participants in the upper Bay and tournament participants in Virginia tributaries,
to shore fishermen throughout the tidal and nontidal portions of the system. It is not known to
what extent catfish are taken for subsistence in the Chesapeake Bay region, however, the large
percentage of small fish taken by anglers surveyed is evidence that catfish are targeted by more
than just pure sport anglers. Catfish are resident species that may experience high levels of fishing
pressure during their spawning seasons (Piavis et al. 1994).
Maryland
In 1993, Maryland issued 218,755 tidal sportfishing licenses and charter boats logged
100,300 trips. Of 12 finfish species kept by anglers in Maryland's portion of Chesapeake Bay,
channel catfish ranks fifth (Feldler and Jacobson 1988). The estimated recreational catfish
landings in Maryland during 1993 was 288,254 pounds (MRFSS data).
Recreational angler surveys in Choptank River during 1993 found less discrimination of
size in the recreational fishery and verifies the 10 inch (250 mm) size limit as a useful conservation
measure (Piavis et al., 1994). However, based on an estimated length of 12" to 14" (300-350 mm)
at first maturity (Fewlass 1980), 49% of the recreational harvest of channel and white catfish
surveyed by MRFSS in Maryland during 1993 were immature fish (Piavis et al. 1994). A creel
survey in Choptank River in 1996 found a disproportionatly low percentage of channel catfish
harvested between 10" and 13" (250-325 mm) and revealed an angler preference for fish in the
16" to 21" (400-525 mm) range (Sadzinski 1997).
Virginia
In 1994, Virginia issued nearly one-half million freshwater fishing licenses and
approximately 80,000 saltwater fishing licenses. Virginia anglers spent an estimated 6.2 million
days pursuing catfish in 1985 (U. S. Department of Interior 1989). Catfish are prized by anglers
for both their culinary value and trophy size potential. Specific creel statistics (e.g., harvest, catch
rates) are unknown for tidal systems; however, a survey by VDGDF underway on the
Chickahominy River (a James River tributary) should yield some insights in this regard.
Potomac River
Elser (1954) conducted a creel survey of the Potomac River in 1954. From Oldtown to
Little Falls (170 river miles, 105 km) recreational harvest of catfish ranked third in importance
(26% of total finfish harvest). During that year, anglers made 89,000 trips (520 trips per mile of
river) and harvested 68,000 catfish (29,000 catfish were released). The most frequent species
harvested was channel catfish. Catfish harvest in creel surveys further downriver in 1960 and 1961
did not rank as high (Frisbie and Ritchie 1963) and was probably due to the lesser abundance of
catfish in the lower portion of the estuary and the greater abundance of other popular sportfish
such as striped bass, bluefish and other summer migrants. White catfish, which are typically found
downstream from channel catfish concentrations, was the principal species reported in the 1960-
61 survey.
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Washington, D.C
Washington, D.C., cites significant angler activity for brown bullheads and channel catfish,
the two most abundant Ictalurid species. White catfish and blue catfish are desirable, however,
their o'ccurance is rare. In the Anacostia River, a tributary of the Potomac, human consumption of
bottom-feeding fish (including catfish) is prohibited through a health advisory. Catfish from the
Anacostia have high levels of PCBs and pesticides accumulated in the flesh and exceed U.S.
Environmental Protection Agency (EPA) limits for consumption. In spite of the health advisory,
catfish are frequently taken by anglers within the watershed (Raj Tilak, D.C. Fisheries
Management Branch, personal communication).
Management
Laws and Regulations
The management strategy for catfish mainly consists of size limits for the commercial and
recreational fisheries. White and channel catfish in Maryland must be at least 10" (250 mm) long,
and no size limits exist for bullheads. In the Potomac River, channel catfish must be 8 inches (200
mm), white catfish must be 10 inches (250 mm), and bullheads must be 6 inches (150 mm).
Virginia currently has no size limits for catfish or bullheads. The three jurisdictions regulate
commercial gear with restrictions on size, design, seasons, and placement. For a summary of all
regulations affecting catfish and bullhead harvest in Maryland, Virginia and the Potomac River,
see Appendix A.
Fishery Management Plan Development
Development of a Fishery Management Plan (FMP) for catfish in Chesapeake Bay was
explored by the Chesapeake Bay Program in 1995. The Fishery Management Plan Workgroup of
the Chesapeake Bay Program's Living Resources Subcommittee recommended that adoption of a
FMP for catfish be delayed for the following reasons: 1) commercially and recreationally exploited
stocks appear healthy; and 2) without a stock assessment, target levels of harvest are unknown
and no management recommendations can be made. Because catfish are heavily exploited, a stock
assessment would be beneficial while the stocks are thought to be healthy. A stock assessment
would allow the fishery to be monitored and future management strategies to be implemented
before harvest grows beyond sustainable levels.
Because migration across jurisdictional lines is naturally restricted due to intolerance of
high salinities, it may be determined that catfish do not need a Baywide, interjurisdictional FMP.
For example, a stock assessment in the upper Bay would not be applicable to catfish stocks in the
Rappahanock or James Rivers, since catfish in Virginia's river systems are isolated populations.
Likewise, management strategies which benefit a population in one area may not be necessary
Baywide. Regional FMPs, applicable to respective regions within the Chesapeake Bay and each
supporting a different species complex, may be more appropriate to address management needs. It
may be possible for catfish to pass between Maryland's portion of Chesapeake Bay and the
Potomac River during years of low salinity and this should also be explored before an
interjurisdictional FMP is developed.
30
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33
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RESEARCH AND DATA NEEDS
Commercial Data Needs
Commercial Reporting Deficiencies
Knowledge of species preference, fishing pressure and relative harvest of each species is
required for effective conservation measures, should they be necessary. Maryland landings were
reported by species for the first time in 1996; however, 38% of catfish landings were "unknown
species" and reporting could continue to be improved. Studies to investigate the size composition of
landed harvest are also needed.
Optimum Harvest
The maximum harvest of catfish species sustainable on a long-term basis is unknown for the
Chesapeake Bay. While commercially and recreationally exploited catfish stocks are believed to be
healthy, it would be most useful to determine the optimum and sustainable level of harvest prior to
any increase in exploitation.
Socioeconomic Effects of Blue Catfish Introduction or Expansion
The presence of blue catfish in Virginia is supported by recreational anglers due to their large
size and aggressive sporting potential. They are a commercially valuable species where populations
are established. However, establishment of blue catfish in areas where commercial harvesters cater
to the live market, which is predominately supplied with channel catfish, could have negative
economic impacts. There is a need to identify potential economic impacts of blue catfish, should their
distribution expand to other states, and create strategies to prevent their expansion.
Recreational Data Needs
Recreational Data
Catfish are an important recreational species in the Bay. Angler surveys conducted by NMFS
(MRFSS data) in tidal estuarine waters do not adequately represent the recreational importance of
catfish in the Bay. In Virginia, catfish are becoming a popular species for recreational tournaments.
With the lack of adequate recreational data, it is difficult to evaluate the need for conservation
measures. Additional data are needed on species preference, fishing pressure and harvest. Isolated
tributaries with high levels of recreational effort may need more intense management than other less-
fished tributaries.
Catch and Release Mortality
Catch and release techniques are widely practiced as a conservation tool by recreational
fishermen. The amount of fish released by anglers and the rate of success associated with such
practices is unknown for catfish. There is some current investigation of this problem in Virginia.
39
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Research Needs
Biology
Few studies exist on catfish biology in estuaries. Growth and age-at-maturity are influenced
by environmental conditions, such as temperature, and studies from differing climatic regions may not
be applicable to Chesapeake Bay. Biological characteristics can vary from one tributary to the next.
More information is needed on sex ratios, fecundity, age composition, standing stock biomass, stock
distribution, feeding, and habitat requirements in each region of the Bay.
Habitat Requirements
Catfish are found in a variety of habitats from fresh to estuarine waters. Some species are
expanding their range and distribution is changing. Habitat requirements and limits of tolerance in
Chesapeake Bay are either changing or unknown. Spawning areas are largely unknown. Further
research is necessary to adequately define habitat requirements for catfish in Chesapeake Bay.
Impacts of Non-Native Catfish Introductions
Effects ofPredation by Catfish on Alosid Restoration Efforts.
The annual spawning migrations of alosid species at one time extended far into Bay rivers,
extending into Pennsylvania and New York via the Susquehanna River, and beyond Charlottesville,
Virginia, via the James River. Shad once supported a large commercial industry, with baywide
landings averaging 20 million pounds annually. By the 1980's landings had fallen to less than one-
twentieth of what they once were. Since the alosid decline, millions of dollars have been allocated to
re-open spawning habitat blocked by dams and other obstructions and harvest of American shad has
been prohibited in Chesapeake Bay since 1980 in Maryland and 1994 in Virginia. Currently, the
Chesapeake Bay Program is developing restoration targets for'shad populations in Chesapeake Bay
and stocking programs are ongoing in Pennsylvania, Maryland and Virginia. Little is known about
the impacts of non-native species, such as channel catfish and blue catfish, which have become
established in areas historically utilized as spawning and juvenile habitat by alosids. Virginia is
currently investigating the effects of catfish predation on alosids in river systems where shad stocking
efforts are targeted.
Channel Catfish Range Expansion and Population Growth in the Upper Bay
Channel catfish are established in the upper Bay mainstem, however, during years of high
freshwater flow, catfish may expand their range southward to areas not historically utilized to any
great extent. Effects of catfish in newly invaded areas on local species are unknown. There is a need
to investigate natural or anthropogenic causes for increases in channel catfish abundance and
distribution, such as increased freshwater flow due to loss of vegetative buffering systems (mainly
forests and wetlands) and increased impervious surface in the upper Bay watershed and identify the
potential biological, ecological and economic impacts. ~
40
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Blue and Flathead Catfish Range Expansion and Population Growth
In Virginia, species distribution is in flux due to competition between native species and
growing populations of naturalized catfish. Blue catfish are an introduced species presently confined
to Virginia tributaries and the Potomac River. Their numbers have been increasing rapidly in Virginia,
and larger fish have been reported annually in recent years (VDGEF unpublished data). They are an
aggressive fish that can reach large sizes and are tolerant of salinities to 11.4 ppt. Blue catfish are
present in low numbers in the Potomac River and the potential for range expansion into the upper
Chesapeake Bay and tributaries has not been investigated. The effects of blue catfish on native
community structure are unknown. In addition, channel catfish may be experiencing displacement in
some tributaries by blue catfish. There is a need to monitor the distribution of blue catfish in Virginia
and the Potomac River, investigate the ecological effects of blue catfish introduction, and evaluate
the potential for blue catfish expansion into the upper Bay.
Flathead catfish populations are present in the James River and the Occoquan River and
reservoir in the Potomac River system. Flatheads are large, aggressive catfish that may compete with
other catfish species, as well as other finfish. Populations are small, but indications are that the James
River population is increasing and should be monitored.
Habitat Alteration
Riparian Buffers
Catfish are known to spawn in freshwater portions of tributaries in dark, sheltered areas. Loss
of riparian forest buffers reduce overhead cover and wood debris utilized as nesting sites. Juveniles
also need cover for protection. The relative importance of riparian vegetation to catfish species should
be examined.
Water Quality
Freshwaters of tidal rivers and creeks are in close proximity to sources of toxic contaminants
and nutrient inputs. Catfish remain in fresh to slightly brackish water throughout their developmental
stages and may be susceptible to concentrated contaminants. Catfish are bottom dwellers and are
susceptible to toxic accumulation in sediments. Catfish that are not highly migratory may be exposed
to contaminants throughout their life cycle. Accumulations of contaminants in catfish tissue has
resulted in the closure of certain areas to catfish fishing for consumption. Current water quality
strategies should be evaluated for their benefits to the catfish resource.
41
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Hopkins University Press, Baltimore, MD.
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APPENDIX A. LAWS AND REGULATIONS
Maryland
Regulatory Agency:
Maryland Department of Natural Resources
Fisheries Service
580 Taylor Ave., Tawes State Office Bldg.
Annapolis, MD 21401
(410) 260-8280
www.dnr.state.md.us
Size Limit
10" size limit for commercial and recreational harvest of white and channel catfish.
Prohibited Harvest Methods
Harvest by snagging and with cross bows is prohibited.
Prohibited: gig, gig iron, purse net, beam trawl, otter trawl, trammel net, troll net, or drag net.
Limit of two hooks or two sets of hooks per rod or line.
Threshing streams is prohibited (exception: Kent and Queen Anne's Counties)
Dynamiting streams is prohibited
June 15 through September 15, a person may not fish from the Conowingo Dam catwalk
using artificial lures or bait other than worms, except bloodworms; dough; scent baits; or
chicken livers.
License Requirements
Commercial harvesters must purchase a Tidal Fish License; commercial harvest is permitted
in tidal waters only.
Recreational anglers must purchase a freshwater fishing license for catfish in nontidal waters
and a Chesapeake Bay Sportfishing License for catfish in tidal waters.
Commercial Nets
Minimum mesh size limit: hedging or lead attached to a fish trap, fyke net, or pound net,
twine size #12 or larger
Minimum mesh size limits: pound net, fyke or hoop net, and haul seine, 1.5"; gill net, -2.5".
Maximum mesh size limit: gill net, 6.0"
Monofilament gill nets prohibited.
The setting of anchored gill nets, pound nets, and fyke or hoop nets or any line of these nets
more than one third the distance across a water body is prohibited except in Baltimore
and Hartford Counties for carp and catfish only.
A minimum unobstructed interval of 200 feet between successive pound or stake nets
For maximum lengths of single line of net stakes, see Annotated Code of Maryland, 4-711.
Hauling any seine or net more than one third of the distance across a water body is prohibited
except in Baltimore and Harford County to catch catfish and carp.
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A person may not drag or haul any seine with two or more vessels propelled by power.
Haul seines may not exceed 1,800 feet in length.
A power winch may be used to haul a seine only if it is anchored in a vessel not propelled by
power and the vessel is anchored in 4 feet of water or less.
A person may not empty a seine on shore or in water less than 12 inches deep and small fish
must be returned to the water.
Minimum of 200' between successive pound or stake nets.
Pound nets may not exceed 1000' to 1650' in length, depending on the area the net is set.
Haul seines are limited to a depth or width of 15' graduating to a width of 22' at the back. A
haul seine may not have a length at its back greater than 100'.
Haul seining is prohibited from Friday midnight until sunrise on Monday in tidal waters.
Pound nets restricted to permitted areas only (see Annotated Code of Maryland, 4-714
through 4-728.
Area Restrictions
Areas may be closed to all fishing seasonally, closed to all fishing except rod, hook and line,
closed to certain types of commercial gear, or otherwise restricted:
For area closures and restrictions in Chesapeake Bay; See Annotated Code of Maryland, 4-
728; in Choptank River, 4-729; in Patuxent River, 4-730; in Susquehanna River, Department
of Natural Resources, title 08 subtitle 02, chapter 05.
For area closures and restrictions by county; See Annotated Code of Maryland, 4-714
through 4-727.
Aquaculture (Department of Natural Resources, title 08 subtitle 02, chapter 14)
Permit required for all aquaculture activities, including culture of native and naturalized
species, the capture of broodstock, and demonstration or experimental culture.
Permits may be issued for catfish, family Ictaluridae.
Aquaculture activities for non-native fish may only be permitted in approved nontidal ponds,
lakes, and impoundments which are constructed to assure that the cultured species are
precluded from entering tidal waters of the State.
Aquaculture activities are prohibited if they will adversely affect wild stocks offish, result in
the release of non-native species into un-confined waters, or result in the contamination of
native or naturalized species.
A facility may not discharge its effluent into Maryland waters without approved treatment.
Brood stock or the progeny of native or naturalized species may be obtained from an out-of-
state supplier, registered to do business in Maryland, and must be certified to be free of
known disease.
Imported hybrid or non-native fish shall be certified free of know diseases.
There are no size requirements for any species of finfish propagated from aquaculture in
nontidal ponds, lakes, and impoundments.
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Virginia
Regulatory Agencies:
Virginia Department of Game and Inland Fisheries
4010W. Broad St.
Richmond, VA 23230
(804) 367-1000
www. state, va. us/~dgif/index. htm
Virginia Marine Resources Commission
PO Box 756
2600 Washington Ave.
Newport News, VA 23607-0756
(757) 247-2200
www. state, va. us/mrc/homepage. htm
License Requirements
Recreational anglers must purchase a freshwater fishing license for catfish in nontidal waters
and a saltwater license for catfish in estuarine waters. Either license may be accepted in
transitional areas of tidal fresh and estuarine.
Maryland saltwater fishing license is reciprocal in Chesapeake Bay and saltwater reaches of
tidal tributaries.
Commercial license and registration required for commercial harvest.
Size and Harvest Restrictions
No size limit.
No creel limit below the fall line
Creel limit above the fall line, 20 of each species per person per day. Bullhead species may
be taken in unlimited numbers.
Commercial fishing activities prohibited on Sundays
Harvest Methods
Use of lime, firearms, dynamite, or other substances to destroy fish are prohibited.
Above the fall line, catfish and bullhead species may be taken by hand, hook and line, seine
(maximum size 4' deep x 10* long), umbrella type net (maximum size 5' x 5' square), cast net
(maximum radius 6"), and hand held bow net (maximum radius 20", maximum handle length
8').
Below the fall line, catfish and bullhead species may be taken by rod and reel, hook and line,
gig, spear, cast net or dipnet.
Trotlines, juglines or set poles may be used for catfish and bullhead harvest. Gear must be
clearly marked and checked daily.
Live bait may be used on trotlines in some counties.
Within designated stocked trout waters, hook and line only is permitted.
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Health Advisories
Consumption advisory in James River near Richmond
Stocking
Unlawful to stock any species in inland waters, with the exception of private ponds, without
written approval from the Dept. of Game and Inland Fisheries.
Potomac River
Regulatory Agency
Potomac River Fisheries Commission
PO Box 9
Colonial Beach, VA 22443
(804) 224-7148 or (800) 266-3904
Potomac River fishing license or license from Virginia or Maryland is required.
Size limits for commercial and recreational:
Channel catfish - 8";
White catfish -10";
Bullheads (brown and yellow) - 6"
Washington, D.C
Regulatory Agency:
Government of the District of Columbia
Environmental Regulation Administration
DC Fisheries Management Program
2100MLKJr. Ave. S.E.
Suite 203
Washington, DC 20020
(202)645-6616
License Requirement
Recreational fishing license required between the ages of 16 and 64.
Commercial harvest is prohibited.
Size and Harvest Restrictions
Minimum size for channel catfish, 12".
Creel limit for channel catfish, 3/person/day.
Harvest Methods
Harvest permitted only by rod, hook and line, not to exceed 3 lines per person and no more
than 2 hooks per fine.
Artificial lures or plugs with multiple gang hooks are considered one unit.
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Harvest by dipnet prohibited except to land a fish caught by hook and line.
Catfish and bullhead harvest with seine prohibited.
Use of explosives, chemicals, firearms, or electricity for catfish or bullhead harvest. is
prohibited.
Health Advisories
Consumption advisory for channel catfish from Potomac and Anocostia Rivers within District
boundaries. Recommend no more than one meal per week of channel catfish with skin and
fat removed.
Stocking
Introduction of nonindigenous species is prohibited in District waters.
Pennsylvania
Sport harvest of panfish, which includes catfish species in Pennsylvania, is restricted to a combined
daily angler possession limit of no more than 50 panfish. Size restrictions and seasonal harvest
restrictions do not apply. Commercial harvest is not permitted in Pennsylvania's portion of the
Susquehanna River system.
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APPENDIX B. CATFISH WORKGROUP
The following were consulted by the FMP Workgroup during the development of this document:
Edward R. Dent
Jessie E. Dent
Carlton G. Edwards
Robert Evans
Marvin L. Harley
Joseph B. Hicks, HI
Jim Jacquette
Stanley E. Oliff, Jr.
Suzie Robertson
Artis Schoen
Peggy L. States
Albert Strong
John P. Travis
Virginia catfish harvester
Virginia catfish harvester
Maryland catfish harvester
Maryland catfish harvester and dealer
Virginia catfish harvester
Virginia catfish harvester
Maryland catfish harvester
Virginia catfish harvester
Maryland catfish dealer
Virginia catfish harvester
Maryland catfish harvester
Maryland catfish harvester
Maryland catfish harvester
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APPENDIX C. GLOSSARY OF TERMS
Atlantic slope: Area of land and waterways that drain into the Atlantic ocean.
CBPO: Chesapeake Bay Program Office
DC: District of Columbia
Gulf slope: Area of land and waterways that drain into the Gulf of Mexico.
LCjo (median lethal concentration): The concentration of a substance at which 50% of test organisms
die.
Length at age: Average length offish from a particular age group (year 1, year 2, and so on) sampled
from a population.
MDNR: Maryland Department of Natural Resources
MRFSS: Marine Recreational Fishery Statistic Survey.
PFBC: Pennsylvania Fish and Boat Commission
ppt: Parts per thousand. Unit of measure for elements or compounds in solution.
VCU: Virginia Commonwealth University
VDGIF: Virginia Department of Game and Inland Fisheries
VIMS: Virginia Institute of Marine Science
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