ENVIRONMENTAL-FACTORS AFFECTING THE EARLY LIFE-HISTORY OF BAY ANCHOVY ANCHOA-MITCHILLI IN GREAT SOUTH BAY, NEW-YORK

For bay anchovy Anchoa mitchilli, 3 life-history parameters were studied in Great South Bay during late spring and summer of 1987 and 1988: intensity of spawning, larval growth rates, and egg and larval mortality rates. Duration of peak spawning season was highly correlated (p < 0.01) with larval food abundance in the field (copepod nauplii + copepodite and adult cyclopoids + copepodite calanoids), but not correlated with salinity or temperature. Cohort mortality rates determined throughout the spawning season were lower in the middle of the peak spawning season (when food availability was maximum) and higher at the begining and end of the spawning season. Since the duration of the high microzooplankton abundance is so short (4 to 5 wk) and because of the high energy requirements of young bay anchovy, it is proposed that adult bay anchovy spawn during the season of maximum food availability thus enhancing offspring survival. When the effects of the type of habitat were analyzed on a local scale, no difference was found between eelgrass and unvegetated areas in: (1) egg or larval density, (2) larval growth rates, (3) egg and yolk sac larvae mortalities. Mortality rates of older larvae (> 3 d old), however, were higher in eelgrass beds than in unvegetated areas. Since microzooplankton abundances were not different among stations, increased mortality rates in the vegetated areas seem to result from higher levels of predation. This suggests that the hypothesis that vegetated areas are used as preferential zones for spawning and nursing may not be aplicable to bay anchovy. When the 3 population parameters studied are considered on a latitudinal basis, it was found that (1) duration of spawning season in Great South Bay is among the shortest reported in the literature, and decreased with increasing latitude; (2) average mortality rates were similar to those reported for populations located at other areas; (3) average larval growth rates tended to be higher in Great South Bay in spite of the lower temperatures during the spawning season. Possible interrelationships among these trends in life-history traits are discussed, and future lines of research on population differentiation are proposed.