NMFS Northeast Fisheries Science Center

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Sandy Hook, NJ–Starfish down, hard clams up. That’s the conclusion of a recently reported study of Raritan Bay hard clams – the smallest and most valuable of which are well known to seafood lovers as “littlenecks.”

Scientists say that local harvesters were able to increase the number of hard clams landed per man per day by about 40% during the 1990s. They suggest this is because starfish, voracious consumers of small clams, virtually disappeared from the area during the same time period.

NOAA Fisheries researchers at the James J. Howard Marine Science Laboratory at Sandy Hook, New Jersey, looked at hard clam and starfish distribution, abundance, and landings in both the New Jersey portion of Raritan Bay and off Connecticut as part of the study. Clammers in Raritan Bay typically use rakes, while those harvesting in Long Island Sound use hydraulic dredges.

“Starfish are tough on shellfish,” says Clyde MacKenzie, one of the scientists who worked on the study and an internationally known expert on commercial shellfish. Starfish destroyed oyster fisheries in Long Island Sound in the late 1950s and early 1960s, he notes. They also eat hard clams, softshell clams, and duckclams (duck feed). “A starfish has been observed to devour 50 duckclams, one-tenth to one-third inch long, in as few as 6 days,” MacKenzie says, “ Most likely, they can eat hard clams at least as fast.”

Researchers found starfish to be extremely abundant in the bay during the 1980s. Sampling dredges used during the study often brought in dozens of starfish following each tow over the bay bottom. In 1992, the dredge samples contained about 36 per tow; in 1993, 10.5 per tow; and only 2 to 4 per tow during 1994-1997, and none in 2000.

A raker harvesting hard clams in Raritan Bay in 1999.

In contrast, prior to the 1990s, clams were confined to small areas of Raritan Bay that the fishermen often raked out in a matter of a few weeks. During the 1990s, fishermen began to find seed clams and littlenecks (which measure about 2 inches long) in thousands of acres in the bay. Landings were consistent between 1990 and 1992 at about 10 million individual hard clams annually, rising to 40 million by 1997, and remaining high since.

Catch of clams in sorting box, Raritan Bay, 1999

The study shows that in Connecticut waters, clams were relatively scarce and starfish abundant until the mid 1980s. The starfish then became scarce and the clams became abundant over hundreds of acres. Clam production afterward increased about twenty-fold. Production remained high from 1986 through 1996, when about 50 boats were harvesting the clams daily. The starfish remained scarce until the mid 1990s, but their numbers then increased sharply and simultaneously clam production declined sharply.

The clams from Raritan Bay must be cleaned of fecal coliform bacteria before sale. Increased landings of hard clams during the 1990s supported establishment of a depuration plant in 1992 in Sea Bright with a capacity of 120 bushels a day, and of a second plant in Highlands in 1995, with a capacity of 240 bushels. Both plants now operate at full capacity during the summer, when the public demand for clams is at its maximum. About 80 rakers supply clams to them daily. About 20 clam rakers also relay their clams daily to certified waters in Barnegat Bay for 30 days of depuration.

The study does not address what factors may be controlling fluctuation in starfish abundance. However, the researcher suggest that it may be related to availability of their prey. They also report on one effective starfish control method, in which large mops were towed over starfish-infested bottoms. The mops are about 14 feet wide and fitted with large cotton bundles. About every 15 minutes, the mops are lifted aboard the towing vessel and the starfish are removed. The mopping method has been an effective starfish control in limited areas in Connecticut for more than 125 years, and may also have been used to control starfish during the heyday of the oyster industry in Raritan Bay from 1825 to 1925.

"It would be an effective measure that could be used if the starfish return and threaten the prosperous clam fisheries of Raritan Bay," MacKenzie says.

An oyster vessel, with starfish mop raised out of the water, in Connecticut in the 1940s.

The paper in which the observations are reported is titled, “A decline in starfish, Asterias forbesi, abundance and a concurrent increase in northern quahog, Mercenaria mercenaria, abundance and landings in the Northeastern United States,” to be published in Marine Fisheries Review, a journal of NOAA’s National Marine Fisheries Service. The authors are Clyde L. MacKenzie, Jr., and Robert Pikanowski. MacKenzie is a specialist in shellfish culture. Pikanowski is a biometrician, the science of describing fluctuations in animal abundances with statistics.

NOAA Fisheries is the federal agency charged with carrying out research, regulatory actions, and natural resource law enforcement to achieve the nation’s goals of sustainable fisheries, healthy coasts, and recovery and protection of listed and protected marine species.

Black circles (above) show abundance of starfish in Raritan Bay in 1992. The arrows point to the few small hard clam beds present in 1992.

Black circles (below) show abundance of starfish in Raritan Bay in 1997. Hard clam beds in 1997 were located throughout the area indicted by outlining.