Age, Growth, Mortality and Food Habits of LarvalStellifer lanceolatus, Cynoscion arenariusandCynoscion nothus(Pisces: Sciaenidae), from the Southern Gulf of Mexico

Abstract

Age, growth, mortality rates and food habits of the larvae of three sciaenid species were studied from the Southern Gulf of Mexico. The material was collected with a Bongo net (505μm mesh), during summer 1992. The Laird-Gompertz growth model was selected over other models because it offered the best approach to the determination of hatching size and gave the highest correlation coefficients. The instantaneous mortality rate for all three species was estimated from the exponential model of decreasing abundance of each (1·0mm) age class. The entire digestive tract was removed from larval specimens in order to identify and quantify its content. The larval size range analysed, and the estimated hatching sizes from the model were 1·52–7·88mm and 1·21mm, 1·51–8·82mm and 0·82mm and 1·33–6·49mm and 0·91mm forStellifer lanceolatus, Cynoscion arenariusandCynoscion nothus, respectively. The growth rate decreased from 10·3% on day 1 to 4·6% on day 27 forS. lanceolatus, 20·1% on day 1 to 3·0% on day 28 forC. arenariusand from 14·5% on day 1 to 7·2 on day 20 forC. nothus. The instantaneous mortality rates were 0·20, 0·17 and 0·25 forS. lanceolatus, C. arenariusandC. nothus, respectively. The small hatching sizes recorded in the study may be due to the relatively high summer water temperatures (>30°C) in the Southern Gulf of Mexico.Hatching sizes are similar to some non-sciaenid species from the Southern Gulf of Mexico. High mortality rate (0·20) ofS. lanceolatusis related to the highest larval density (2·776 larvae 100m−3) and the lowest average growth rate (7·0%). Copepods were the main larval food item for all three species; there were also relatively high percentages of pelecypods in smallS. lanceolatuslarvae. Very few specimens simultaneously had two different kinds of prey, which could be a consequence of the patchy distribution of prey. The low proportion of empty digestive tracts suggests that there was a good food supply during that summer.