46 



BIOLOGICAL REPORT 31 



and oysters are the dominant shellfish species in the 

 bay, followed to a lesser extent by the edible blue 

 mussel, which although easily gathered and delicious 

 has not reached the popularity it has in Europe. 



The most widespread shellfishery in Buzzards 

 Bay is the hard-shelled clam or quahog, Mercenaria 

 mercenaria ( Fig. 4.3 ). Cape Cod is as the north- 

 ern boundary to large-scale distribution of the spe- 

 cies ( Belding 1916), which is a warm water mol- 

 lusk. Quahogs grow in shallow and deep water; 

 how ever, they were primarily harvested in shallower 

 waters until the advent in 1982 of a deep water 

 dredge fishery in the bay. Mercenaria populate 

 sandy to muddy sand bottoms generally in areas 

 where salinity is above 15 ppt and can be found 

 virtually along the perimeter of the bay. They bur- 

 row into the sediments and extend their siphons into 

 the water column to feed. These clams are quite 

 tolerant to short-period stresses such as bottom wa- 

 ter anoxia; they can also survive during harvest when 

 they are out of water for long periods by "clamming 

 up." remaining with their shells closed until condi- 

 tions improve. Larger individuals are extremely 

 hardy and can survive days of anoxia or emerge 

 from deep burial (tens of centimeters) caused by 

 shifting sands or overwash during storms. Although 

 these clams grow quickly and achieve marketable 

 size in 3-4 years, they may live up to 25 years. 





2 



Fig. 4.3. Quahogs {Mercenaria mercenaria), left, and 

 shoft-shelled clams (Mya arenaria), right. Photo by 

 D Goehringer 



Soft-shelled clams, Mya arenaria (Fig. 4.3). 

 generally occur in sandy or muddy sediments in pro- 

 tected harbors and inlets and in salt marsh creeks, 

 burrowed in the sediment with siphons extending 

 into the water column. Their fragile shells are less 

 tolerant to disturbance and are more easily broken 

 than those of most other species of clams in the 

 Buzzards Bay region. Because their shells do not 

 close tightly (a portion of the siphon protrudes from 

 the shell), they have limited tolerance to anoxia and 

 can suffer high mortalities from sulfide accumula- 

 tion under low oxygen conditions resulting from ei- 

 ther natural or anthropogenic causes. Because these 

 shellfish are more prevalent in soft organic-rich sedi- 

 ments, occasional low oxygen conditions are likely 

 due to oxygen depletion in bottom waters that re- 

 sults from microbial decomposition of this organic 

 matter. Intolerant of salinities less than 5 ppt, they 

 frequently inhabit low-energy embayments where 

 organic matter can accumulate yet with sufficient 

 flushing or limited freshwater inputs to maintain high 

 enough salinity for reproduction and growth. The 

 combination of low-energy, high organic matter en- 

 vironments and sensitivity to hypoxia can result in 

 mass mortalities of this species, as have occurred in 

 Cape Cod Bay (G.R. Hampson, Woods Hole 

 Oceanographic Institution, personal communica- 

 tion). Because of the somewhat fragile nature of 

 their shells, there has been recent interest in hydraulic 

 dredging to decrease losses during harvest and in- 

 crease yields over traditional hand-tonging. 



In addition to infaunal bivalves. Buzzards Bay is 

 recognized for its high productivity of the epibenthic 

 bay scallop, Aequipecten irradians (Fig. 4.4; 

 Gutsell 1 930). Cape Cod is considered the north- 

 em limit for the scallop, which is less common in the 

 colder waters to the north (Goode 1887; Davis 

 1 989). The commercial scallop fishery in Buzzards 

 Bay began in New Bedford in 1 870, principally in 

 the lower Acushnet River and Clarks Cove, and 

 rapidly expanded to the upper regions of the bay 

 (Davis 1 989). Today, there are many areas around 

 the bay where scallops still sustain an important com- 

 mercial fishery, primarily in the Westport River but 

 also in the Acushnet River and Clarks Cove on the 

 western shore. West Falmouth and Wings Neck 



