A NOTE ON A SPAWNER—RECRUIT RELATIONSHIP FOR A HEAVILY EXPLOITED BIVALVE: THE CASE OF NORTHERN QUAHOGS (HARD CLAMS), MERCENARIA MERCENARIA IN GREAT SOUTH BAY NEW YORK

The Town of Islip, NY has collected a long-term data set (1977–2004) on northern quahog (hard clam), Mercenaria mercenaria, abundance. The data comprise approximately 350 duplicate 1 m2 samples each year taken with a clam shell bucket. All samples were sieved through a 6.4 mm sieve and the hard clams enumerated by size. In addition, clam landings data for the town waters are available for the same time period. Clam populations have declined from their peaks in the 1970s to very low levels in the 1990s and 00's. These dramatic shifts in population abundance have made the exploration of spawner/recruit relationships possible. A number of alternate models were attempted, but based on knowledge of the biology of the species and other factors, all but two did not appear to be plausible. The two models (2nd order polynomial and Log) yielded high r2 values and intercepted the 0 axis between 0.5 and 0.75 adult clams m−2 indicating a density dependent effect on recruitment. The polynomial model also suggested a carrying capacity level of about 5 adult clams m−2 and a density dependent upper level of density. This is the first time a spawner recruit relationship has become apparent for hard clams.