Meta-analysis of growth and mortality rates of net cultured sea scallops across the Northwest Atlantic

Abstract

Scallops are one of the most heavily traded and widely consumed seafood in the world and the vast majority of production comes from aquaculture. In 2018, the global value of scallop aquaculture was over $5.8 billion USD with farms producing nearly three times the biomass as the entirety of the wild harvest. North American (specifically U.S. and Canadian) scallop aquaculture lags far behind the rest of the world. The U.S. is home to a valuable Atlantic sea scallop (Placopecten magellanicus) fishery. Yet demand for scallops far outstrips supply and the U.S. imports an almost equal amount, by value, of farmed scallop products. To capitalize on this trade imbalance, U.S. and Canadian aquaculturists have been developing a farmed sea scallop (hereafter scallop) industry, employing the Japanese practices of suspended net culture and the sale of whole and “roe-on” products. We examined the combined effects of culture method and environment on scallop shell growth and mortality. We compiled all published net cultured scallop shell growth and mortality rates recorded in the last 45 years in the Northwest Atlantic. Using generalized additive models (GAMs), we identified significant nonlinear interactions between growth, mortality, environmental conditions, and culture methods applicable from Maine, USA to Newfoundland, Canada. Optimum shell growth occurs within a temperature window of 10–15 °C. Growth is higher in pearl nets than in lantern nets, and is also highly sensitive to stocking density, which has large implications for farm sizes and thinning practices. Maximum mortality occurs at the highest temperatures in our dataset (~17 °C), while stocking density is only a significant predictor of product loss at high densities. Scallops are also more susceptible to mortality at shell heights under 25 mm. Both mortality rates and shell height growth rates were lower in the late spring and early summer after accounting for temperature effects. Careful temperature based site selection and proactive low density stocking can mitigate the effects of intraspecific competition and reduce handling related mortality. Identifying lease sites that provide both optimal environmental conditions and adequate space for low density net culture will be an important step in expanding scallop aquaculture in the Northwest Atlantic.