264 



CoLislal c& Marine Ecosystems — Uiir Living Resources 



84 85 86 87 88 89 90 91 92 

 Year 



of submersed grasses 

 aquatic vegetation or 

 Chesapeake Bay, 



Fig. 1. Area 

 (submersed 

 SAV) in the 

 1984-92. 



Status and Trends 



The status and trends of key habitats and 

 species in the Chesapeake Bay are based on 

 multiple annual surveys conducted by state and 

 federal agencies. Perhaps the most comprehen- 

 sive is a survey of the bay's submersed aquatic 

 plant community; each year, the extent of sub- 

 mersed aquatic vegetation (SAV) is estimated 

 by aerial photography of the entire bay and the 

 tidal ponions of its major tributaries (Orth and 

 Moore 1983). Wetland areas are likewise esti- 

 mated from aerial photographs and have been 

 extrapolated for the watershed from a finite 

 number of sites in various geographic strata for 

 three time periods (Tiner and Finn 1986; Tiner 

 et al., U.S. Fish and Wildlife Service, unpub- 

 lished data). Approximately every 8 years, 

 forested areas are estimated for each state in the 

 bay watershed by the U.S. Department of 

 Agriculture Forest Service's Forestland 

 Inventory from satellite imagery (Chesapeake 

 Bay Program 1993). 



Many aquatic animal species that are sur- 

 veyed annually (including those addressed here) 

 support commercial and recreational fisheries 

 or hunting and bird watching. Oyster, blue crab, 

 striped bass, and American shad populations are 

 estimated from commercial landings, and are 

 augmented at times with surveys that are inde- 

 pendent of fishery statistics, such as numbers of 

 oyster spat that set each year, estimates of the 

 biomass of spawning striped bass, or numbers 

 of juvenile striped bass per seine haul (the 

 young-of-year index). Waterfowl have been 

 counted during their wintering season on the 

 bay by the aerial Midwinter Surveys since the 

 I940's. 



Submersed Aquatic Vegetation (SAV) 



Beginning in the late 1960's and continuing 

 into the 1970's. the distribution and abundance 

 of a community of 20 species of submersed 

 grasses declined throughout the bay because of 

 nutrient enrichment, increased loads of sus- 

 pended sediments, and other factors (Stevenson 

 and Confer 1978; Orth and Moore 1983). In 

 1978 the first aerial survey estimated 16.500 ha 

 (40.700 acres) of SAV in the bay (Anderson and 

 Macomber 1980). The next year. 15,400 ha 

 (38.000 acres) were documented (Orth et al. 

 1985); since that time, annual surveys have 

 shown modest but continual increases in SAV 

 coverage to an estimated 28,600 ha (70.600 

 acres; Orth et al. 1993; Fig. 1). Recent increas- 

 es represent gains in brackish mid-bay regions 

 and are teinpered somewhat by slow or no SAV 

 recovery in freshwater areas in the upper bay 

 and by the spread of the exotic species hydrilla 

 (Hydhlla verticillata) in the tidal freshwater 

 poilions of the Potomac River. 



Wetlands 



The status and trends for more than a million 

 acres of wetlands in the Chesapeake Bay water- 

 shed have been estimated over two time peri- 

 ods, from the mid-1950's to the late 1970's and 

 early I980's (Tiner and Finn 1986). and from 

 this period to 1989 (Tiner et al, USFWS, 

 unpublished data). Dominant wetland types 

 include nontidal forested wetlands (60% of total 

 wetlands), nontidal shrub-scrub wetlands 

 (10%), and salt and freshwater marshes (10% 

 each). 



Losses occurred in all of these wetland types 

 during the period from the mid-1950"s to late 

 1970""s and early 1980's. About 9% of the 

 watershed's salt marshes were lost to dredging, 

 impoundment, and filling. Nontidal wetlands 

 declined by nearly 6% as a result of being 

 drained and converted to agriculture or 

 impounded to form ponds, lakes, and reservoirs. 

 During the 1980's, losses continued; the rate of 

 marsh loss declined, while forested wetland 

 losses increased. Overall, there was an estimat- 

 ed net loss of 0.5% of estuarine wetlands and a 

 net loss of 2.0% of palustrine wetlands (rough- 

 ly equal to tidal and nontidal wetlands) during 

 the I980's. These trends mirror historical losses 

 over the past 200 years (Dahl 1990). 



Forests 



An estimated 95% of the Chesapeake Bay 

 watershed was forested before European settle- 

 ment; around 58% remains today (Chesapeake 

 Bay Program 1993; Fig. 2). This percentage is 

 declining for the first time in over a century 

 because of recent forest clearing for urban and 

 suburban development. Forest clearing has pro- 

 ceeded unevenly over the watershed, with some 

 drainages intact and others as much as 85% 

 cleared. 



Oysters 



Oyster landings in Chesapeake Bay have 

 experienced a 95% decline since 1980 and are 

 estimated to be at their lowest recorded level 

 (Kennedy 1991; National Marine Fisheries 

 Service. Annapolis. Maryland, unpublished 

 data; Fig. 3a). Although reproductive success of 

 the oyster remains high (as measured by larval 

 oyster, or spat, set on oyster reefs and other suit- 

 able substrates; Maryland Department of 

 Natural Resources. Oxford, Maryland, unpub- 

 lished data), populations have suffered from 

 harvest to low levels, two parasidc diseases 

 (Dermo and MSX), habitat loss (including 

 decreased water quality), and predation. 



Blue Crabs 



Blue crab populations in the Chesapeake 

 Bay, as indicated by commercial landings data. 



