Authors

EN Powell
R Mann

Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

2005

Journal

Journal Of Shellfish Research

Volume

24

Issue

2

First Page

517

Last Page

530

Abstract

We report results of a survey explicitly focused on ocean quahog recruitment in the Mid-Atlantic Bight. The recruitment survey resampled all NMFS survey sites south of Hudson Canyon and a selection of sites north and east of Hudson Canyon off the Long Island coast over the entire depth range of this species with the exception of the most inshore reaches off Long Island. More ocean quahogs were encountered, on a per tow basis, in the vicinity of and north of Hudson Canyon. The proportion of recruits in the size-frequency distribution was higher in the south and the most recent recruitment events were concentrated there. Analysis of the 104 size-frequency distributions delineated regions of recent recruitment, areas that have not seen significant recruitment for many decades and areas that received heavy recruitment some decades previously but not recently. Overall, the survey suggests that three regionally distinctive processes determine the size-frequency distributions of ocean quahog assemblages and recruitment therein. The area northeast of Hudson Canyon is unique in the regionally extensive uniformity of size-frequency distributions among sampled assemblages. the near absence of recent recruitment and the presence of large numbers of older recruits, 65-80 mm in size. The inshore (by ocean quahog standards) area off New Jersey is unique in the dominant presence of the largest size classes of ocean quahogs and the remarkable absence of significant recruitment over an extraordinary time span. The area south of 39 degrees N is unique in the widespread presence of relatively young recruits, including some animals with ages within the time span of the present fishery. Recruitment events in ocean quahog populations, although rare in the sense of occurring only once in a score or two of years, are frequent in the context of the +200-year life span of this species, yet also rare in the context of stock survey timing and fishery dynamics. This study strongly supports the assumption that long-lived species recruit successfully only rarely when at carrying capacity. This study also suggests that the history of recruitment over the last perhaps two-score years, revealed by this survey, may be a poor measure of the recruitment dynamics to be anticipated over the next two-score years when the population abundance is reduced to what is anticipated to approximate the biomass at maximum sustainable yield. Given the long time span required for ocean quahogs to grow to fishable size, a substantive disequilibrium may exist between the recruitment anticipated from the relationship of adult biomass to carrying capacity and the contemporaneous number of recruits for minimally 20 y after adult abundance is reduced from circa-1980 carrying capacity to biomass. maximum sustainable yield.

Keywords

Recruitment; Ocean Quahog; Arctica; Fisheries Management; Size-Frequency Distribution

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