Bioenergetic analysis of the effects of temperature and prey availability on growth and condition of northern cod (Gadus morhua)

Abstract

Atlantic cod (Gadus morhua) stocks of the Northwest Atlantic have experienced steady decreases in growth rate since 1989 and in physiological condition since 1988. The declines have been attributed to various factors, including size- selective fishing pressure, anomalously low temperature fields, and a decline in available prey. The precise balance of these factors is unknown. We applied simple correlation models to determine that bottom water temperature and capelin ( Mallotus villosus) biomass together explain 52% of the interannual variance in mean condition of 2J3K cod and 23% of the interannual variance in 2J3KL mean cod growth rates. Bioenergetic models can potentially improve our understanding of the mechanisms behind these relationships because they allocate energy as a function of environmental parameters such as water temperature and prey consumption. We developed a bioenergetic model for Atlantic cod to determine whether temperature could explain the observed decreases in growth rate of northern cod stocks. Our results suggest that the low growth rates of 2J3K northern cod observed in recent years are not due to physiological temperature limitation, while the growth rates of cod inhabiting cooler waters on the northern Grand Banks (3L) may, at least in certain years, be temperature limited.