Endtuujered Species Pacts
&EPA
Pkofo source: B. Moose Peterson/USFWS Digital Library
The delta smelt is a threatened
species. Threatened species
are plants and animals whose
population numbers are so
low that they may become
endangered in the future.
Endangered species are
plants and animals that are
in immediate danger of
becoming extinct.
The U.S. Environmental
Protection Agency's (EPA)
Endangered Species Protection
Program (ESPP) will help
ensure that pesticide use does
not jeopardize the survival of
listed species.
Delta Smelt
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Description and Ecology
Status Threatened, listed March 5, 1993.
Critical Habitat Designated December 19, 1994.
Appearance The delta smelt typically grows to 2.4-2.8
inches in length. Except for the steel-blue sheen on its sides,
its delicate, slender body appears nearly transparent. Its eyes
appear large. Its relatively small mouth has little, pointed
teeth on the upper and lower jaws. A small, fleshy fin (adi-
pose fin) sits atop the back between the dorsal fin and the
tail.
Range Delta smelt are found only in the Sacramento-
San Joaquin estuary in California. Historically, populations
were found from Suisun Bay, east to the Delta area, and
then upstream in the Sacramento River to about Isleton
and upstream in the San Joaquin River to about Mossdale.
Locations are dependant upon stage in the life cycle and
extent of water outflow from the Sacramento and San Joaquin
Rivers. When outflow was greater, delta smelt congregated in
upper Suisun Bay and the Montezuma Slough. As a result of
increasing water diversions and drought, the center of species
abundance has shifted east to the Sacramento River channel
in the Delta.
Habitat This shift in the species center of abundance
arises from the fact that while the delta smelt is a euryhaline
(saltwater tolerant) species, it is seldom found where sea
water makes up more than 1/3 of the total water. The
locations of delta smelt are tied to the freshwater side of
the mixing zone (where the salt and freshwater meet). As
drought and river water diversions reduce the outflow of
freshwater downstream, the mixing zone is drawn upstream
into the river channels. There the mixing zone is compressed
and limited to the deeper river channels where the current
may be faster and more turbulent, shoals absent, and the
usual species richness (microzooplankton) of the mixing zone
limited. Larvae require high densities of microzooplankton.
These high densities occur when the mixing zone occupies a
large geographic area such as Suisun Bay, which has shoals,
sloughs, wetland edges, and suitable spawning substrate at
depths less than 13 feet. Low outflows keep adult delta smelt
and their larvae upstream in the deep, narrow channels of
the rivers and delta, where food production is limited by the
inability of sunlight to penetrate water depths.
Reproduction and Life Cycle while spawning
can occur from January through July, low outflow tends
to eclipse the season from March to mid-May. Spawning
occurs in sloughs and shallow, edge-waters of channels in
the upper Delta. Each female broadcasts 1,200-2,600 eggs.
Eggs sink to the bottom and adhere to rocks, gravel, tree
roots, and submerged vegetation or branches. With optimum
temperatures eggs hatch in 9-14 days. Feeding begins in
another 4-5 days.
Initially the larvae have an oil globule that buoys them just
above the bottom where they are able to feed on rotifers
and other microscopic prey. After the swim bladder develops,
the 0.6-0.7 inch long larvae are able to rise higher in the
water column and be whisked downstream to within or just
upstream of the mixing zone. There prey should be abundant
and their own growth rapid. By August the juveniles are 1.6-
2.0 inches in length. At this time the marked absence of older
adults suggests they may not live much beyond spawning.
This defines the delta smelt as an annual species. For the next
several months the growth rate of the delta smelt juveniles
slows down while their bodies ready for reproduction.
The prey of the delta smelt are small crustaceans and insect
larvae, and consist primarily of a native copepod, Eurytemora
affinis. Recently an exotic copepod species from the Yangtze
area of China and Japan, Pseudodiaptomus forbesi, has been
replacing E. affinis. While delta smelt appear to consume this
exotic species, the full impact of its presence is unknown.
Another exotic species, the overbite clam, was discovered
in Suisun Bay in 1986. After a multi-year drought that
eliminated much of the benthic community of Suisun Bay, the
ttyjxmtesus irmAp&djiam
Office of Pesticide Programs (7507P)
http://www.epa.gov/espp/
February 2010

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population of overbite clarris spread. Its numbers and their
filtration rate can impact the phytoplankton population and,
as a result, the overall food web. Striped bass, white catfish,
and black crappies prey upon delta smelt.
While populations of delta smelt have fluctuated from year to
year, drought from 1987 to 1992 severely impacted the delta
smelt numbers. A rebound in the population the following
year was attributed to a wetter winter and spring. Since then
the numbers, of what once was one of the most common
pelagic fish in the Sacramento-San Joaquin estuary, have
dropped significantly. Critical habitat was designated for
this species on December 19, 1994. However, by 2005 the
population of delta smelt was perhaps as little as 2.4% of the
estimated population in 1993 when the delta smelt was listed
as "threatened."
Recovery Plan The U.S. Fish and Wildlife Service (FWS)
developed a recovery plan for the delta smelt in 1996.
Recovery pians outline reasonable actions that FWS
believes are required to recover or protect listed species.
FWS prepares recovery plans, sometimes with the assistance
of recovery teams, contractors, state agencies, and others.
Recovery plans do not necessarily represent the views nor the
official positions or approvals of any individuals or agencies,
other than FWS, involved in the plan formulation. Approved
recovery plans are subject to modification as dictated by new
findings, changes in species' status, and the completion of
recovery tasks.
Delta Smelt Information Sources
Primary Reference Beacham, Walton, Castronova,
Frank F., and Sessine, Suzanne (eds.), 2001. Beacham's
Guide to the Endangered Species of North America, Gale
Group, New York. Vol. 2, pp. 908-912.
Listing Notice U.S. Fish and Wildlife Service, 1993.
Federal Register 58, No. 42, pp. 12854-12864, March 5,
1993. http://ecos.fws.gov/docs/federal__register/fr2235.pdf
Critical Habitat Designation u.s. Fish and wildlife
Service, 1994. Federal Register 59 No. 242, pp. 65256-
65279, December 19, 1994. http://ecos.fws.gov/docs/
federal_register/fr2751.pdf
Recovery Plan U.S. Fish and Wildlife
Service. 1996. Sacramento_San Joaquin Delta
Native Fishes Recovery Plan. U.S. Fish and Wildlife
Service, Pacific Region, Portland, Oregon. 195 pp.
http://ecos.fws.gov/docs/recovery_plan/961126.pdf
Pkofo of the. Scut Joa^uin-SacraMterUo Rww Veita, courtesy of D&ise Poiasckek.
Vkffto of SttiswK Bay courtesy of Mike Hui^hin^.
Native cop-eft&d Eurytemwa, affum (ma^fufvedj Left), and introduced
for best (riykt), prey of the deita, smeit. Both, images
courtesy ofjeffery ft. Cordeti, C&fzep-od Qauery, University of WaMuntjton..
&EPA

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