Date of Award

Summer 2018

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Ocean Science and Technology

Committee Chair

Eric N. Powell

Committee Chair Department

Ocean Science and Technology

Committee Member 2

Roger Mann

Committee Member 3

Chet F. Rakocinski

Committee Member 3 Department

Ocean Science and Technology


Atlantic surfclams, Spisula solidissima, are long-lived bivalve molluscs with dispersive larval stages. Surfclam patchiness throughout the U.S. Exclusive Economic Zone (EEZ) has declined from the 1980’s to the present in all assessed regions (Delmarva, New Jersey, Long Island, Southern New England, and Georges Banks). Warming of Mid-Atlantic bottom waters is driving the surfclam stock into new habitat and extirpating the surfclams from nearshore areas. Based on a species distribution function model, the small surfclams appear to inhabit a greater area than the large market-size surfclams across the entire stock. The wider distribution of recent recruits relative to the fishable stock, however, positions the species well to respond to changing bottom water temperatures as Mid-Atlantic warming continues.

Atlantic surfclams support a major commercial fishery in the western North Atlantic Ocean. The stock is not and historically has not been overfished nor has overfishing occurred; however, in recent years landings per unit effort have declined. A species distribution function model was used to assess the effective area occupied by surfclams for 5 study regions. Three independent statistical analyses of the stock-recruitment relationship found little evidence of a significant association in any of the 5 regions, suggesting that factors besides spawning stock biomass are primary determinants of recruitment success. The recruitment index obtained from the NEFSC-NMFS survey across the range of the stock, as a consequence, is unlikely to usefully presage changes in abundance of the fishable stock due to a bias in mortality of juveniles inshore.