MEPS 585:81-98 (2017)  -  DOI: https://doi.org/10.3354/meps12384

ABSTRACT: Geographic differences in the age structure of 4 populations of ocean quahogs Arctica islandica throughout the range of the stock within the US exclusive economic zone were examined. The ages of animals fully recruited to the commercial fishery (≥80 mm shell length) were estimated using annual growth lines in the hinge plate. The observed age frequency from each site was used to develop an age-length key enabling reconstruction of the population age frequency for the site. Within-site variability was high for both age-at-length and length-at-age; a single age-length key could not be applied and would not result in accurate age estimates for populations throughout the northwestern Atlantic. For most sites, the oldest living animals recruited 200-250 years BP, coincident with the ending of the Little Ice Age. The southern populations had the oldest animals, consistent with a presumed warming from the south. All sites experienced an increase in recruitment beginning in the late 1800s to early 1900s depending upon site, whereupon the populations reached carrying capacity and remained so characterized subsequently through more or less continuous low-level recruitment. The lag in population expansion following recruitment of the oldest living animals is consistent with the extended time to maturity in the species and suggests that the oldest animals record initial colonization near the end of the Little Ice Age. All 4 populations show evidence of high recruitment capacity when below carrying capacity and relatively continuous recruitment when at carrying capacity.

KEY WORDS: Ocean quahog · Arctica islandica · Age-frequency distribution · Age-length key · Recruitment