United States Environmental Protection Agency Chesapeake Bay Program Annapolis MD 21403 Research and Development EPA-600/S3-82-082 Jan. 1983 Project Summary Distribution and Abundance of Waterfowl and Submerged Aquatic Vegetation in Chesapeake Bay Robert Munro and Matthew Perry Waterfowl populations in Maryland and Virginia portions of Chesapeake Bay were examined during long-term (1890-1970) and current (1972- 1980) periods to identify trends in their distribution and abundance. Comparisons were also made between State and Atlantic Flyway populations and waterfowl species distributions among survey areas. Distribution and abundance of submerged aquatic vegetation (SAV) among waterfowl survey areas in Maryland were sum- marized for seven plant species during nine years (1971-1979). These data (SAV species combined) were used to test the hypothesis that annual varia- tion in area populations of waterfowl was related to variation in the abun- dance of SAV, following an adjustment for annual variation in the general abundance of waterfowl. The distribu- tion and abundance of SAV species declined in Maryland waters during the 1970s. There were few statistical- ly significant relationships between distribution and abundance of water- fowl and SAV. But there was an implied biological relationship, since the most important waterfowl winter- ing areas were also among the most abundantly vegetated areas. This report was submitted in partial fulfill- ment of Interagency Agreement No. EPA-78-D-X0391 by the U.S. Fish and Wildlife Service, Migratory Bird and Habitat Research Laboratory under the sponsorship of the Chesa- peake Bay Program, U.S. Environmen- tal Protection Agency. This Project Summary was devel- oped by EPA's Chesapeake Bay Program, Annapolis, MD, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction The Chesapeake Bay is the most important wintering area in the Atlantic Flyway for more than 1.5 million waterfowl, including Canada geese (Branta canadensis), whistling swans (Cygnus columbianus columbianus). canvasbacks (Aythya valisineria), ruddy ducks (Oxyura jamaicensis), common goldeneyes (Bucephala clangula ameri- cana), redheads (Aythya americana). black ducks (Anas rubripes), and mal- lards (Anasplatyrhynchos). The estuary also serves as a resting area for birds that migrate farther south. Of the 45 spe- cies native to North America, 30 migrate through or winter in Chesapeake Bay. Large beds of submerged aquatic vegetation (SAV), especially widgeon- grass (Ruppia maritima), wild celery (Vallisneria americana),and sago pond- weed (Potamogeton pectinatus), have ------- traditionally been important to the Bay's population of waterfowl. The decline of the grasses, a major source of food for the birds, prompted this examination of historic and current relationships between waterfowl and SAV. Procedure/Methodology The U.S. Fish and Wildlife Service (USFWS) conducts annual population surveys of Chesapeake Bay waterfowl. Although information may be affected by weather conditions, birds not found, and birds found but not counted, these surveys constitute the only long-term source of information on waterfowl distribution and abundance. These surveys were analyzed so that popu- lation comparisons between pre- 1970 (long-term) and 1972-1980 (current) periods could be made. United States populations were used as baseline measures to indicate species trends. Species had to compose at least five percent of the Atlantic Flyway population to be considered in this study. Waterfowl feeding habits were tabu- lated according to species, time period (pre-1960,1960s, and 1970s), and organ source (gizzard, gullet, or unknown). (See Table 1.) This information, collected by Stewart1 during the 1950s, Rawls2 during the 1960s, and supplemented with current data, provided the informa- tion necessary to examine relationships between waterfowl and SAV as a food source. Distribution and abundance records of SAV taken from results of summer surveys conducted by the USFWS and Maryland Wildlife Administration during 1971-1979 were studied to determine the trends of SAV populations. Linear regression and analysis of variance techniques were used to examine rela- tionships between waterfowl and SAV. Results/Conclusions Reductions in SAV populations af- fected the distribution and abundance of waterfowl species that were histori- cally dependent on SAV and could not adapt to the changes. Some species left the area while others changed their feeding habits. The SAV population as a whole declined dramatically in the 1970s. Vegetated sample stations in Maryland waters declined from approximately 29 percent during 1971 to 8 to 15 percent since 1973. Important waterfowl food plants which were abundant during the late 1960s became less prevalent in the Bay by 1973. Examples include widgeon- 7able 1. Summary of the Incidence of Plant Material in the Diet of Waterfowl that Winter in Chesapeake Bay Percent plant material, and sample size ()a Species Whistling swan Canada goose Ruddy duck Bufflehead Common goldeneye Canvasback Greater scaup Lesser scaup Ring-necked duck Redhead American Widgeon Blue-winged teal Green-winged teal Black duck Gadwall Mallard Pintail Pre-1960 74.7 65.2 24.6 53.1 71.3 40.4 51.4 65.4 99.0 97.1 90.7 84.9 74.1 99.0 98.9 97.5 (50f-< (25) (20f c (14) (47) (36) (29) (17) /oc |b~c (OO/ (35) (21) (10) (55) (21) (25) (36)*-' 1960s* 100.0 - 32.6 36.9 52.3 37.2 56.7 94.0 76.6 97.7 - 100.0 93.5 - 94.5 96.4 (221) ( -) (27) (45) (246) ( 9) (82) (10) (77) (121) ( -) (13) (131) ( -) (134) (47) 1970s - - 20.8 25.1 8.6 32.8 57.9 - 96.6 - - 91.3 82.6 - 92.7 95.2 '( '-) ( -) (30) (21) (273) (40) (76) ( -) ( 7) ( -) ( -) (29) (57) ( -) (84) (27) ailnless otherwise noted, aggregate percentages are from gizzard samples. * Taken from Rawls, C. K. (in prep.). Food habits of waterfowl in the upper Chesapeake Bay, Maryland. University of Maryland Center for Environmental and Estuarine Studies. 140 pp. ^Aggregate percentages are from samples for which organs were not recorded. grass, sago pondweed, horned pondweed and wild celery. Table 2 illustrates trends in Bay grass populations, among waterfowl survey areas, for nine years. Over 600 sampling stations of shoal water habitats were established to monitor these trends. By 1979 each of the 20 areas had depleted supplies of SAV. The Lower Choptank River, for example, had 25.5 percent of its stations vegetated in 1971. By 1979, however, this total fell to 12.8 percent. Eastern Bay, another important winter- ing area for waterfowl, fell from 21.4 percent in 1971 to 11.1 percent in 1979. Widgeongrass, the most important food item of widgeon and black ducks, was the most abundant and widely distributed species in each of nine annual surveys. Low populations of widgeon, pintails, and redheads, which were predominantly vegetarian in nature, were correlated with the overall decline of SAV. Diving ducks, including canvasbacks and redheads, were most affected by the SAV decline. Diving ducks have small wings and legs set back on their bodies making walking difficult. They need water to run across prior to flight and are thus unable to feed in dense marshes or agricultural fields. Redhead populations, which subsist on SAV, declined in numbers. Apparently they could not change their diets and exist in an area with reduced SAV populations. Canvasbacks, on the other hand, incorporated Baltic clams (Macoma spp) and other invertebrates into their diets, and therefore remain as important members of the wintering waterfowl population of the Bay. Puddle ducks, which feed by dabbling at the water's surface, were historically more dependent on vegetation. Puddle duck populations, as a group, are presently at one third their former level. Pintail and widgeon populations are now nearly absent from Maryland wintering areas. Other puddle ducks, such as black ducks and mallards, have also decreased. Whistling swans survived the decline of SAV by foraging on the land. This species now depends more on the availability of unharvested cereal grains from agricultural fields than on SAV. The population of Canada geese contin- ued a long-term increase in numbers during the 1970s. Like swans, Canada geese rely on cereal grains from fields around the Bay. Recommendations The declining numbers of waterfowl that winter in the Chesapeake Bay are cause for concern. Biological links exist between abundance of grasses and cer- tain waterfowl populations in the Bay. ------- Table 2. Frequency Occurrence of Measurable SA V (Species Combined) in Maryland Waterfowl Survey Areas During the Years 1971-79 Percent with Vegetation, and Sample Size" Survey area" Lower Choptank River Manokin. Annemessex R. Chester River Eastern Bay Smith Island (Maryland) Bloodsworth, South Marsh Island Patapsco R., Aberdeen P.G. Honga River Bayshore. Hooper Island Magothy - Severn Rivers Susquehanna Flats Miles River Wye River Little Choptank River Upper Choptank River Fishing Bay Sassafras River Northeast, Elk, Bohemia R. Bayshore, Kent County Patuxent River Total 1971 25.5(51) 33.3 (57) 41.7 (36) 21.4(28) 47.1 (17) 27.5 (40) 1.9 (52) 30.0 (30) 39. 1 (23) 33.3 (27) 36.4 (22) 12.5 ( 8) 9. 1 (1 1) 10.0 (30) 11.1 ( 9) 7.9 (25) 20.0 (10) 5.0 (20) 8.3 (12) 0.0 (50) 19.2(624) 1972 20.8 (48) 12.7(55) 13.9 (36) 20.8 (24) 27.3 (1 1) 13.6(44) 0.0 (50) 23.3 (30) 17.4(23) 7.4 (27) 0.0 (30) 37.5 ( 8) 36.4 (1 1) 3.3 (30) 20.0 (10) O.O (25) 0.0 (10) 0.0 (23) 0.0 ( 6) 0.0 (45) 9.6(613) 1973 14.9 (47) 10.7(56) 14.7(34) 14.3 (28) 25.0 (12) 8.7(46) 2.0 (50) 3.3 (30) 4.3 (23) 14.8 (27) 0.0 (30) 12.5 ( 8) 18.2(11) 0.0 (30) 0.0 (JO) 0.0 (25) 0.0 (10) 0.0 (23) 0.0 (12) 0.0 (50) 6.2(629) 1974 14.3 (49) 17.6(34) 11.8(34) 10.7(28) 23.5(17) 7.0 (43) 3.8 (52) 3.3 (30) 8.7(23) 14.8 (27) 6.7(30) 12.5 ( 8) 36.4 (1 1) 0.0 (30) 0.0 ( 9) 0.0 (25) 0.0 (10) 0.0 (23) 0.0 (12) 2.0 (50) 7.2(610) 1975 0.0 5.8 11.1 14.8 11.8 (47) (52) (36) (27) (17) 0.0 (43) 4.5 3.4 4.3 6.7 25.0 9.1 0.0 0.0 0.0 0.0 0.0 0.0 (22) (29) (23) ( 0) (30) ( 8) (11) (30) (10) (24) (10) (22) (12) 0.0 (47) 3.8 (552) 1976 21.7(46) 14.0 (57) 8.6(35) 18.5 (27) 17.6(17) 0.0 (45) 1.9 (52) 3.4 (29) 4.3 (23) 0.0 (25) 0.0 (29) 28. 6 ( 7) 18.2 (1 1) 0.0 (30) 0.0 (10) 0.0 (25) 0.0 (10) 0.0 (22) 0.0 (12) 0.0 (49) 5.7(628) 1977 8.2 (49) 12.5 (56) 16.7(36) 14.8 (27) 0.0(17) 0.0 (46) 7.7(52) 0.0 (30) 4.3 (23 J 7.4 (27) 0.0 (30) 25. Of 8) 9. 1 (1 1) 3.3 (30) 0.0 (10) 0.0 (25) 0.0 (10) 0.0 (23) 0.0 (12) 0.0 (49) 5.0 (638) 1978 6.1 (49) 0.0 (55) 30.6 (36) 11.1 (27) 5.9(17) 0.0 (46) 3.8 (52) 3.3 (30) 0.0 (23) 11.1 (27) 0.0 (29) 12.5 ( 8) 9.1 (11) 3.3 (30) 0.0 (10) 0.0 (25) 0.0 (10) 0.0 (22) 0.0 (12) 0.0 (50) 4.2 (636) 1979 12.8(47) 0.0 (66) 22.2 (36) 1 1. 1 (27) 5.9(17) 0.0 (45) 5.8 (52) 0.0 (30) 0.0 (23) 14.8 (27) 6.9 (29) 0.0 { 8) 9. 1 (1 1) 0.0 (30) 0.0(10) 0.0 (24) 0.0 (10) 0.0 (23) 0.0(12) 0.0 (48) 4.4 (631) "Data from the files of PWRC, Laurel, Maryland. "Frequency occurrence of SA V averaged over years, when multiplied by the extent of shoal habitat (<2.44 m at mlw) in an area, determined the sequence of survey areas used above. Decreases in distribution and abun- dance of SAV directly affect certain spe- cies of waterfowl. Recovery of SAV re- sources will encourage the return of SAV-dependent waterfowl that annual- ly migrate through the area. Scientists should continue to study factors leading to the declension of SAV and how such changes affect oth'er aspects of the Bay ecosystem. References 1. Stewart, R.E. 1962. Waterfowl Populations in the Upper Chesapeake Bay. U.S. Fish and Wildlife Service. Special Science Report. Wildlife No. 65. 208 pp. 2. Rawls, C.K. In prep. Food Habits of Waterfowl in Upper Chesapeake Bay Basin. University of Maryland Center for Environmental and Estuarine Studies. 140pp. Robert Munro and Matthew Perry are with the U.S. Fish and Wildlife Service, Laurel, MD 20810. William A. Cook was the EPA Project Officer (for information, see contact below). The complete report, entitled "Distribution and Abundance of Waterfowl and Submerged Aquatic Vegetation in Chesapeake Bay," (Order No. PB 82-266 156; Cost: $16.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 For information contact David Flemer at: Chesapeake Bay Program 2083 West Street, Suite 5G Annapolis, MD21403 ------- United States Environmental Protection Agency 6> •if U.S. GOVERNMENT PRINTING OFFICE. 1983 659-OI7/O88 Center for Environmental Research Information Cincinnati OH 45268 Postage and Fees Paid Environmental Protection Agency EPA 335 Official Business Penalty for Private Use $300 USS ENVIR2PROTtC1ION AtiENCY CHICAGO IL 6060a ------- |