Document Type

Report

Department/Program

Virginia Institute of Marine Science

Publication Date

12-1990

Series

Special Scientific Report No. 125

Abstract

Large populations of softshell clams persist only in relatively shallow, sandy. mesohaline portions of Chesapeake Bay. These areas are mostly in Maryland, but can also occur in the Rappahannock River. Virginia. In some other portions of the bay, especially polyhaline portions. sparse populations of soft shell clams persist subtidally. Restricted populations exist intertidally.

Softshell clams grow rapidly in Chesapeake Bay, reaching commercial size in two years or less. They reproduce twice per year, in spring and fall, but probably only fall spawnings are important in maintaining population levels. Major recruitment events do not occur in most years. despite heavy annual sets.

Softshell clams are a major food item for many predator species. Major predators on juveniles include blue crabs. mud crabs, flatworms. mummichogs. and soot. Major predators on adults include blue crabs, eels. and cownose rays. Some other species that may depend heavily on softshell clams include overwintering and migrating ducks. geese, and swans. and estuarine populations of muskrats and raccoons. Diseases may play an important role in regulating populations of adult softshell clams, and hydrocarbon pollution is linked to increased frequency of disease. Oil pollution does the most widespread and persistent damage to softshell clams. and may also induce disease. Heavy metals. pesticides, and other contaminants can be extremely toxic, but the harmful effects to clams do not last when the contamination abates . The main concern with these toxin compounds is the chance of bioaccumulation by softshell clams, thereby passing the compounds on to predators or to humans.

Siltation caused by storm events. dredging operations. or erosion, can smother clam populations. Eutrophication, enhanced by nutrient inputs from sewage or agriculture. is not yet known to have affected softshell clam populations. but the danger exists.

Keywords

Mya arenaria -- Habitat -- Chesapeake Bay (Md. and Va.); Clams -- Habitat -- Chesapeake Bay (Md. and Va.); Bivalves

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