Effects of fish length and temperature on the timing of peak spawning in capelin (Mallotus villosus)

Some characteristics of Newfoundland capelin (Mallotus villosus) changed during 1991-1994. Peak spawning times were later than most years in the 1980s and fish were smaller. These changes occurred during a period of below-normal sea temperatures. We tested the effects of sea temperatures during maturation and mean size of mature fish on peak spawning times using regression analysis and found significant negative relationships for both independent variables. Results of a stepwise regression showed that fish length and sea temperature during maturation were equally important and together explained about 80% of the spawning time variation. We suggest that maturation and migration are closely linked to seasonal warming and the zooplankton cycle. Given the high spawning mortality of capelin, it seems that this linkage favours maximum gonad production rather than adult survival. Knowledge of spring water temperatures would permit some prediction of capelin spawning time. However, the data series for mean length used in this analysis is not useful for predicting spawning time.