A Bioenergetics Based Comparison of Growth Conversion Efficiency of Atlantic Cod on Georges Bank and in the Gulf of Maine

Several authors state that foraging conditions and food web dynamics may be contributing to declines in Atlantic cod stocks. Therefore, it is essential to take a food web perspective to understand the complicated array of potential interactions affecting marine communities. The widely used Wisconsin Bioenergetics Model uses an energy-balance approach calculated on a daily time step and can be used to evaluate the effect of changes in prey resources on growth or food consumption. Bioenergetics models have been made for many important fishes within the Great Lakes. However, few have been developed for US Northeastern Continental Shelf fish species. Growth performance of Georges Bank and Gulf of Maine Atlantic cod during 2004 was examined using a bioenergetics model and available data on gut contents and growth of different ages. Growth efficiency, calculated from daily growth and consumption rates, was used as a measure of growth performance. Overall growth performance for Atlantic cod was significantly lower at Georges Bank than in Gulf of Maine. Monthly individual consumption demand and specific growth rates for Atlantic cod calculated from the bioenergetic model were significantly higher on Georges Bank than in the Gulf of Maine. Increasing water temperatures approached the upper limits of thermal tolerances for cod in Georges Bank, possibly leading to decreasing growth efficiencies. Growth efficiency of cod in the Gulf of Maine was less variable than on Georges Bank due to the more homogenous temperatures and energetic content of diets found in the former location.