The response of a larval white hake population to the oceanographic regimes of 1974 and 1975 in St. George's Bay, Nova Scotia

Abstract

Differences in the biological and physical oceanographic features of St. George's Bay, Nova Scotia were established for 1974 and 1975. The biomass of particles <330um, suitable sized food for fish larvae, was greater in 1974. An initially high level in 1975 plummetted early in the study period after the passage of a tropical storm. Although the Bay warmed up 2 weeks earlier in 1975, temperatures were the same over most of the season. After establishing these oceanographic differences, responses in the larval white hake, tenuis, population were sought. Differences in the rate of warming appeared to be responsible for the earlier peak (2 weeks) of 1975 abundance curves for the neuston and lOm depths. The apparent consequences of the differences in the biomass of suitably sized prey organisms were more striking. Although the 6 morphometric measures of body form selected for comparisons showed no significant differences at the .01 level, larvae weighed more in 1974, the year of greater absolute food abundance, and had higher condition factors. Despite a larval abundance 1.5 times higher in 1975, subsequent recruitment by that year class to the fishery was very low. These results suggest the importance of measuring nutritional condition when using larval abundance as a predictor of recruitment since the period of high mortality occurs some time after early feeding.