Egg Production by the Bay Anchovy Anchoa Mitchilli in Relation to Adult and Larval Prey Fields

Abundances of copepod nauplii, copepodite/adult copepods, and the larvae of iteroparous anchovies (primarily the bay anchovy Anchoa mitchilli) were monitored in Tampa Bay, Florida (USA) at 2 wk intervals for 2 yr. All possible pairings of the 3 time-series variables yielded significant positive correlations. Nearly all (>98%) of the collected anchovy larvae occurred with prey (nauplius) densities higher than those reported to affect larval starvation (<100 >l ^-1 ). The larval association with abundant prey could be explained as (1) the remnants of earlier larval starvation, or (2) spawning being concentrated in zooplankton-rich waters. To evaluate the 2 explanations, the diet of adult A. mitchilli was analyzed, and egg/adult prey surveys were conducted across a 290 km ² area of Tampa Bay. In 5 of the 6 spatial surveys, A. mitchilli egg abundance was correlated with the abundance of calanoid copepods, a principal adult prey item. Calanoids (primarily adult Acartia tonsa ) were never correlated with net plankton biomass or with the eggs of the bay anchovy's congener, Anchoa hepsetus . Calanoids were aggregated near sites of stable freshwater discharge during a dry season, but became dispersed as discharge increased during a rainy season. Among spatial surveys, egg abundance exhibited a strong nonlinear relationship with calanoid aggregation (r ² = 0.96, n = 6, p = 0.001). Collectively, these findings suggest that the bay anchovy's size-specific fecundity is related to adult prey availability, with adult prey availability being represented by a combination of abundance and patchiness. We discuss relationships between spawning pattern and environmental instability, and suggest that iteroparity serves to fine-tune reproductive effort to environmental parameters that are relevant to larval survival.