Warming bottom water temperatures are increasingly impacting sensitive sedentary bivalves within the Mid-Atlantic, including the economically important Atlantic surfclam, Spisula solidissima. A primary characteristic of the surfclam is the regional variability in average maximum size as measured by the von Bertalanffy parameter L-infinity (Linf) varying from around 100 mm to above 170 mm. Variation in maximum length in this species is likely due to its wide geographic distribution coupled with its genetic capacity to reach considerable size under appropriate conditions. The influence of bottom water temperatures on surfclam maximum size is a good example of the temperature-size rule, which states that animals of larger size will be found in cooler climates. The physiological basis for this rule is found in the surface area to volume relationship relating the surface area of the gill (ingestion) to the volumetric demand of tissue maintenance (respiration). These two temperature-dependent physiological attributes cap maximum size and shape the gradient with temperature.
The challenge, as global warming persists, is to evaluate the influence of temperature-determined variations in surfclam size frequency relative to fishery performance under the present regulatory framework that includes a landings size-limit of 4.75″ (~120 mm). As warming continues and Linf declines, smaller clams are more often caught and the probability of the landings size-limit impacting the fishery increases. An agent-based fisheries model, SEFES, is applied to directly evaluate the impact of size-limited growth on fishery performance and its regulatory framework. SEFES utilizes a newly developed algorithm capable of predicting trends in the von Bertalanffy parameters k and Linf under present-day bottom water temperatures and in the coming years as warming of the northwestern Atlantic continues. This model provides a unique opportunity to holistically simulate the implications of size limits, and the entire impact of the size-temperature rule, as global warming continues.