Egg production rates of Calanus finmarchicus in the western North Atlantic:: effect of gonad maturity, female size, chlorophyll concentration, and temperature

Egg production rates of Calanus finmarchicus were measured in the Labrador Sea (spring) and on the Scotian Shelf (spring, summer, and autumn), in conjunction with indices of gonad maturity and food availability, female body size, surface layer temperature, and surface nitrate concentrations. Egg production rates were often two to four times higher than any previously reported at similar temperatures. Estimates of egg production rates of populations were most closely related to the proportion of reproductively mature females (as measured by a gonad stage index) and female size. Specifically, the gonad stage index (proportion of females capable of spawning) was correlated with the proportion of females that spawned during 24-h incubations, and female size determined the clutch size (i.e., number of eggs produced). Although there were detectable effects of food and temperature on egg production rates, they were generally weaker than the effect of female gonad maturity. Thus, over the broad spatial and temporal scales of this study, the reproductive (i.e., life history) status of a population was more important in determining its egg production rate than direct external factors (i.e., temperature and food conditions).