Abstract

Because of the potential link between forage species year-class strength and variability in recruitment of important commercial and recreational fish species, the population dynamics and recruitment variability of key forage species has become a focus of study in recent years. Understanding the size-specific vulnerability of forage species is especially important because changes in availability and vulnerability of forage species to predators (i.e. size-structure, abundance) may have direct implications on the overall recruitment success of piscivorous fish stocks. The bay anchovy (Anchoa mitchilli) is a particularly important forage species that plays a crucial role in estuarine trophic dynamics throughout its range. In some systems the bay anchovy comprises 60-90 % of piscivorous fish diets. With an understanding of the mechanisms that affect large-scale trends in mortality of such forage species, it will be possible to better predict how populations of commercially and recreationally valuable species will respond to fluctuations in population structure (i.e. availability, vulnerability) of the forage base. The growth-mortality hypothesis predicts that larger, faster growing individuals might experience lower mortality, because they are able to more quickly pass through the vulnerable early developmental stages. This study determines to what extent juveniles of A. mitchilli experienced relatively fast growth rates during early developmental periods, i.e. were surviving individuals faster growers as larvae and young juveniles? Larvae and juveniles were collected weekly at seven stations across coastal Mississippi during summer 2004. Variability in growth rates for specific 7 day age classes was compared using daily otolith growth increments. Comparisons were made both over time using a longitudinal analysis, and across age classes using a cross sectional analysis, to help characterize how size-selective mortality may structure a population of forage fishes.

PDF Preview