Assessment of the Relationship of Stock and Recruitment in the Atlantic Surfclam Spisula solidissima in the Northwestern Atlantic Ocean

Abstract

Atlantic surfclams support a major commercial fishery in the western North Atlantic Ocean with landings consistently between 15,000 and 25,000 metric tons since 1982. The stock is not and historically has not been overfished nor has overfishing occurred; however, in recent years landings per unit effort have declined. Surfclams are a biomass dominant on the continental shelf and a bellwether of climate change in the northwestern Atlantic. This study investigated the relationship of broodstock and recruitment during a period when Mid-Atlantic warming initiated a shelf-wide shift in the surfclams range. A species distribution function model was used to assess the effective area occupied by surfclams for five study regions (Delmarva, New Jersey, Long Island, Southern New England, and Georges Bank). The effective area occupied by small surfclams was consistently much greater than that for large ($120 mm) surfclams. Three independent statistical analyses of the stock-recruitment relationship found little evidence of a significant association in any of the five regions, suggesting that factors besides spawning stock biomass (SSB) are primary determinants of recruitment success. Interannual variability in recruitment, in part associated with variations in larval transport and in part associated with spatially different rates of mortality post-settlement, is an important source of uncertainty and warming bottom waters driving surfclams into new habitat may decouple any inherent interaction between recruits and SSB. A recruitment index obtained from a fishery-independent survey across the range of the stock, as a consequence, is unlikely to usefully presage changes in abundance of the fishable stock. The wider distribution of settlers relative to the fishable stock, however, positions the species well to respond to changing bottom water temperatures as Mid-Atlantic warming continues.

Potential Repercussions of Offshore Wind Energy Development in the Northeast United States for the Atlantic Surfclam Survey and Population Assessment

“…However, there is little evidence that Atlantic surfclams have a stock–recruitment relationship (Timbs et al. 2018). Hence, this stock is not presently limited by larval supply, and increased biomass resulting from maintenance of larger animals in wind energy lease areas may not necessarily lead to an increase in population abundance.…”

The intermingling of benthic macroinvertebrate communities during a period of shifting range: The “East of Nantucket” Atlantic Surfclam Survey and the existence of transient multiple stable states

“…The influence of warming bottom water temperatures promoting an offshore shift in the surfclam's range is well described (see review in Hofmann et al, 2018). This process has been ongoing since the 1970s and is well documented off New Jersey by a shift in the range core (Timbs et al, 2018;Weinberg, Powell, Pickett, Nordahl, & Jacobson, 2005) and mass mortality along the inshore range boundary (Kim & Powell, 2004) off Delmarva. and NEFSC (2017a) documented the same trends as far north as Georges Bank.…”

“…These two species occupy the cold temperate (Virginian Province—Hale, ) and boreal (Acadian Province—Hale, ) sides of the north‐temperate advancing temperature boundary. As the surfclam responds more rapidly to warming temperatures with an across shelf shift in range (Hofmann et al, ; Timbs, Powell, & Mann, ), the two species presently occupy an ecotone extending along much of the mid‐Atlantic region (Powell, Ewing, & Kuykendall, ). The dynamics of this geographically extensive ecotone remain unstudied, save for its documentation.…”

How Uncertainty in Natural Mortality and Steepness May Affect Perception of Stock Status and Fishery Sustainability in Atlantic Surfclam: A Simulation Analysis

“…The Atlantic surfclam (Spisula solidissima) is a historically important resource for the north-and Midatlantic commercial fisheries (McCay et al 2011, Hofmann et al 2018), though uncertainties in population dynamics complicate determination of management targets (Munroe et al 2016, Timbs et al 2018. The 2016 stock assessment determined that the surfclam stock was not overfished (SSB > SSB Threshold ) and overfishing was not occurring (F > F Threshold ; NEFSC 2017).…”