Status and Trends of Hard Clam, Mercenaria mercenaria, Populations in a Coastal Lagoon Ecosystem, Barnegat Bay–Little Egg Harbor, New Jersey

Bricelj, V.M.; Kraeuter, J.N., and Flimlin, G., 2017. Status and trends of hard clam, Mercenaria mercenaria, populations in a coastal lagoon ecosystem, Barnegat Bay–Little Egg Harbor, New Jersey. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay–Little Egg Harbor, New Jersey. This review examines the historical and current status of hard clam, Mercenaria mercenaria, populations in the Barnegat Bay–Little Egg Harbor (BB-LEH) Estuary using New Jersey State stock assessments and published studies and evaluates their potential for rehabilitation under present environmental conditions. This estuary has experienced increasing urbanization, population growth, bulkheading, and changes in watershed use. Clam populations have decreased markedly since the 1960s, and in LEH, substantial areas are now devoid of clams. Landings of wild-caught hard clams, and commercial and recreational clam licenses have all declined. There is no evidence that eutrophication and hypoxia are directly responsible, and historical fishing pressure has not been adequately documented. Low salinities restrict the distribution of hard clams in northern BB. High-density, microalgal picoplanktonic blooms in summer, characteristic of this ecosystem, can be poor food for hard clams. Brown tides (Aureococcus anophagefferens), which cause concentration-dependent growth inhibition of both larval and juvenile stages and may cause reduced reproductive effort of adults, have recurred in this estuary. Microalgal quality is likely a more critical factor affecting hard clam populations than total biomass. There are ∼67,296 total acres of classified shellfish area in BB-LEH, with 83.8% approved year-round for shellfish growing. Restricted or prohibited harvest areas are generally found along shorelines and creeks, and there have been no recent substantial changes in the percentage of classified waters. With an overall clam abundance of 0.94 clams m−2 in 2001, densities over a large portion of LEH were then at or below the threshold (∼0.8 clams m−2) suggested to be required for the maintenance of a self-sustaining population, pointing to potential recruitment limitation. The 2011 survey suggests a rebound, but there were still large areas devoid of clams (40% of LEH), and 81% of the area was devoid of sublegal clams. The data suggest that an increased mortality rate may be a significant factor in reducing hard clam populations, but the cause(s) remains unknown