Ocean quahogs [Arctica islandica (Linnaeus, 1769)] are the longest-lived, noncolonial animal known today, with a maximum life span exceeding 500 y. Ocean quahogs are a commercially important bivalve, inhabiting the continental shelf of the North Atlantic Basin. Although considerable information exists on the growth and physiology of A. islandica, limited information is available regarding recruitment; accordingly, sustainably managing the fishery is a challenge. To investigate long-term recruitment trends, the age of ocean quahogs from Georges Bank which were fully recruited to the commercial fishery (>80 mm shell length) was determined by analysis of annual growth lines in the hinge plate. Ages of animals representing the fully recruited size range were used to develop an age—length key, enabling reconstruction of the population age frequency. The population age frequency showed that the Georges Bank population experienced an increase in recruitment beginning in the late 1890s. Initial settlement, documented by a few ocean quahogs that were much older, occurred much earlier, in the early 1800s. Following the late 1890s increase in recruitment, the population expanded rapidly reaching carrying capacity in 20–30 y. Recruitment was more or less continuous after this expansion, consistent with maintenance of a population at carrying capacity. Unusually large year classes were not observed, nor were significant periods of high recruitment interspersed with periods of low recruitment. The relationship of growth rate with age for the oldest clams was assessed using the time series of yearly growth increments and the resulting relationship fitted to three models (von Bertalanffy, Gompertz, and Tanaka's ALOG curve). The ALOG model was clearly superior because it allows for persistent indeterminate growth at old age, rather than the asymptotic behavior of the other two and because it allows for a rapid change in growth rate at what is presumed to be maturity.
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Vol. 36 • No. 1