Recruitment Processes of Anchovy in Chesapeake Bay: Predation Effects, Spawning Sites and Larval Transport

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Fluctuations in adult fish abundance are caused by variable recruitment levels, a consequence of high and variable mortality during the early life stages. Causes of high mortality of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay are believed to be primarily from predation by abundant jellyfish, which are both temporally and spatially patchy. "Windows" in which anchovy cohorts can develop under low predation pressure are hypothesized to provide a mechanism for successful recruitment. A conceptual model predicts that anchovy larvae will be transported up-bay and into the tidal tributaries by estuarine hydrodynamics. This model and related hypotheses will be tested in this investigation. Bay-wide cruises will map abundances of anchovy eggs, larvae and predators, relating them to environmental gradients that may affect survival, growth and distribution. Area- specific age-frequency distributions, growth rates and mortality rates will be estimated from daily increments in larval otoliths. Areas of origin, and probable transport trajectories of late-stage larvae and juveniles will be determined from otolith microchemistry by analysis of strontium:calcium ratios, which should indicate salinity zones where larvae hatched. Direct measures of predation rates will be obtained in large drifting mesocosms under ambient environmental conditions. Chesapeake Bay is an appealing ecosystem within which to study recruitment processes. Abundant cohorts of bay anchovy eggs and larvae are presented with wide ranges of temporal and spatial variability in predator abundances, food availability and well- described estuarine circulation patterns. The bay-wide analysis here will provide new information of mechanisms that affect survival and recruitment potential of fishes.