Hard Clams, Scallops and more

Shellfish communities are characterized by high species diversity.

a photo of three different mollusksSince 1993, the Maryland DNR Shellfish Program has been conducting hard clam (Mercenaria mercenaria) population assessments in the Coastal Bays on an almost annual basis. The results of the 2002 Hard Clam Survey, conducted in June, are presented here, as well as a comparison with the previous year’s findings. The status of the bay scallop population (Argopectin irradians) is also presented. Eastern oyster (Crassostrea virginica) populations existed historically in the Coastal Bays.

HARD CLAMS

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Hard clams have declined over the past three decades but have been relatively stable for the past 10 years.

The findings of the 2002 survey reflected the varying characteristics and circumstances distinguishing the individual Coastal Bays and sub-bay areas. While average clam densities in most of the bays were statistically stable, two areas experienced declines (both in Southern Chincoteague). Based on data collected it seems reasonable to attribute the decline in part to fishing mortality.  This is corroborated by anecdotal reports that the majority of the clamming fleet had shifted their effort to these areas during the 2002 season.  For the most part this has resulted in lower recruitment than in the recent past, although there was an unexpected boost in the number of small clams in one of the bays (Isle of Wight).

Overall, the highest average density of hard clams among the Coastal Bays was in Isle of Wight Bay, followed by Sinepuxent Bay and the southeast quadrant of Chincoteague Bay. The lowest average hard clam density among the bays was in Newport Bay, though not statistically different from Assawoman Bay and the western half of Chincoteague Bay. The east side of Assawoman Bay had an unusual (for that bay) increase in the number of sublegal clams in 2002, although densities were still much lower than in the adjoining Isle of Wight Bay.

Hard Clam Young-of-the-Year Surveys

The findings of the two young-of-the-year surveys were disappointing. In 2000, only about 12% of the stations had 0+ year class clams, and none had more than two clams in a grab. The survey found highest sets in Sinepuxent and Isle of Wight Bays, with only two small clams elsewhere. The 2001 set appeared to be even lower than the previous year. Very few post-settlement clams were in evidence, occurring in only six percent of the stations. More young-of-the-year clams were caught in Isle of Wight Bay than in the rest of the bays combined; only two were found in the southern half of Chincoteague Bay (out of 48 samples). Preliminary estimates indicate that only about one percent or less of the young-of-the-year clams found in September survive to the sub-legal size class.

BAY SCALLOPS

Bay scallops have been found in most bay segments, although in low numbers.

a photo of scallopsIn addition to assessing the hard clam population, the Survey provided information on other mollusks, including bay scallops. The news on this species is very encouraging. After three years of steady decline, the fledgling population of bay scallops has shown signs of rebounding. Perhaps more exciting than the modest reversal in density trends is the dramatic expansion of their range.

When scallops first started to appear in the Coastal Bays during the mid-1990's after an absence of over 60 years, their distribution was confined to some relatively small areas in southern Chincoteague Bay, particularly along the east side from the Virginia state line to Cedar Islands. Then a patch of scallops were found in Rum Harbor just outside of Green Run Bay, where MD DNR had planted and successfully raised over 1 million seed scallops to spawning size in 1997 and 1998. The Rum Harbor scallops, possibly the offspring of the MD DNR introduced stock, were a discrete group separated from the Virginia line population by about two miles. At around the same time, National Park Service personnel reported finding scallops in Sinepuxent Bay, making this the third discrete area inhabited by scallops in the bays. This year scallops were found at locations along the east side of Chincoteague Bay from Sinepuxent Bay to Virginia. In addition, scallops were recorded north of the Ocean City Inlet, both in Isle of Wight and Assawoman Bays, for the first time since their latest return to the Maryland Coastal Bays. Considering the inadequate habitat conditions for this species that had existed in the upper bays until recently (low salinity prior to 1933, absence of eelgrass beds afterwards), these scallops are possibly the first to occur in this area in well over a century. Thus they now inhabit every one of the Coastal Bays with the possible exception of Newport Bay.

Although the majority of the scallops were found in seagrass beds, including the recently established beds in the upper bays, some were caught on unvegetated bottom. Surprisingly, two scallops were captured on the muddy bottom in the mouth of Turville Creek, an environment not usually associated with this species. Clammers have also reported finding scallops on shelly bottom out towards the middle of Chincoteague Bay.

The size of most of the captured scallops was around 35 mm (about 1˝ in.) shell length, meaning they had set in 2001. This is an important indication that recent reproduction and recruitment was successful, a critical factor for a species whose life span is only about two years. Unlike hard clams, which can live over 30 years, scallops only have two or three opportunities to produce offspring, and if there is a year class failure the entire population can crash. The largest scallop was a hefty 76 mm (3 in.) caught in the vicinity of South Point.

Although the long-term viability of the bay scallop population is still in question, the reversal of the trend in declining numbers and extraordinarily rapid range expansion is a big step toward their establishment in the Coastal Bays. 

OYSTERS

Presently there are no viable oyster populations inhabiting subtidal bars.

The eastern oyster (Crassostrea virginica) was once prized for its salty flavor, providing profitable livelihoods to generations of watermen in the remote villages along the shores of the bays. In addition to their commercial value, oysters are ecologically important as reef builders, contributing structure and hard substrate to a rich community or organisms associated with them in an otherwise soft-bottom environment.

The demise of the Coastal Bays "Chincoteague" oyster has resulted in the loss of a critical functional component of the ecosystem and the gradual disappearance of a significant structural element as well.

Episodic natural events, in particular the opening and stabilization of the Ocean City Inlet, fundamentally changed the Coastal Bays ecosystem, creating higher salinities in which oyster populations, whether natural or cultured, and the industry they supported, could no longer exist. Small, relict populations still exist intertidally at a few locations throughout the Coastal Bays, with occasional spatfall on structures such as riprap, pilings, and bridge supports. Despite the long-term absence of significant oyster populations, two diseases, Dermo (Perkinsus marinus) and SSO (Haplosporidium costalis), are active in the Coastal Bays.

If you have any questions about Maryland's Coastal Bays, 
please feel free to e-mail, Cathy Wazniak, or call (410) 260-8638.

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