GeoduckPanopea generosaGrowth at Its Southern Distribution Limit in North America using a Multimodel Inference Approach

Abstract

The Pacific geoduck Panopea generosa is distributed throughout the North Pacific temperate zone from Alaska to Baja California and is described as a species that reaches large sizes, has prolonged longevity, and exhibits slow growth. This study assessed the individual growth and population structure of the P. generosa population located at its southernmost geographic distribution limit. Shell length and total weight data were obtained from a commercial fishery established on Punta Canoas, Baja California. Individual age was determined by counting growth lines for 243 organisms. The results revealed the following averages: shell length (SL), 113.5 mm; total weight, 511.8 g; age, 12.5 y. The relationship of SL to total weight showed negative allometric growth (b = 2.16). Size-at-age data were adjusted to von Bertalanffy, Gompertz, logistic, Johnson, and Schnute growth models according to the multimodel inference (MMI) approach. The best candidate growth model was selected based on the Akaike information criterion (AIC) and the Schwartz—Bayesian criterion (SBC). The AIC indicated that the Schnute growth model was the best candidate growth model, whereas the SBC showed the Johnson growth model was best. These growth models indicate that between 7 y and 8 y of age, organisms reach 75% of their estimated asymptotic length (SL, ∼103 mm), and although the growth rate decreases subsequently, growth continues up to 25 y (maximum age observed). The MMI approach applied to the analysis of growth in Panopea species identified particular population attributes that are not observable via the von Bertalanffy model. The population of P. generosa from Punta Canoas exhibited smaller mean SL, lower mean weight, an age structure with fewer age classes, and slower growth when compared with northern populations in Washington state and British Columbia, Canada.