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Recruitment dynamics

Development of an Age-Frequency Distribution for Ocean Quahogs (Arctica islandica) on Georges Bank

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 >80 mm in shell length was determined by analysis of annual growth lines in the hinge plate. Ages of animals were used to develop an age-length key, enabling reconstruction of the population age frequency. Initial settlement occurred in the early 1800s. The population experienced an increase in recruitment beginning in the late 1890’s, after which the population expanded rapidly reaching carrying capacity in 20- 30 years. Recruitment was more or less continuous after this expansion, consistent with maintenance of a population at carrying capacity. 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.

Pace, S. M., Powell, E. N., Mann, R, Long, M. C., Klinck, J. M. 2017. Development of an Age-Frequency Distribution for Ocean Quahogs (Arctica islandica) on Georges Bank. J. Shellfish Res. 36: 41-53.