Linking ETM physics, zooplankton prey, and fish early-life histories to striped bass Morone saxatilis and white perch M. americana recruitment

Abstract

Transport to and retention of early-life history stages within the estuarine turbidity max- imum (ETM) region may be an important component of recruitment success of the anadromous striped bass Morone saxatilis and the white perch M. americana. This hypothesis was evaluated with spatially resolved surveys of the physical and biological characteristics of the upper Chesapeake Bay estuary during 5 cruises, 3 in May 1998 and 2 in May 1999. Gradients in depth-specific patterns of larval abundance and zooplankton prey were evaluated with respect to salinity, temperature and total suspended solids (TSS). Although physical conditions in the upper estuary differed between cruises and years, the spatial patterns in distribution of larvae and potential prey were consistent and tracked changes in salt front and ETM locations. A statistical analysis suggested that location relative to the ETM explained a significant amount of variability in concentrations of eggs, yolk-sac larvae, and larval prey, and that prey concentrations accounted for a significant amount of variability in con- centrations of feeding larvae. Transport to the ETM region probably occurs during the egg (striped bass) and yolk-sac larva (white perch) stages and results in retention of early-stage feeding larvae in a zone of high prey concentrations. Physical conditions in the ETM region differed markedly between a low freshwater-flow year (1999) and a high flow year (1998), and abundances of striped bass and white perch post-yolk-sac larvae were significantly lower in 1999. Recruitment variability was poorly correlated with spawning stock biomass, but spawner-recruitment models that incorporated spring freshwater discharge explained an additional 41% (striped bass) and 30% (white perch) of the variability in recruitment. Annual changes in freshwater flow could control larval survival and recruitment by modifying the physical and biological characteristics of the ETM region.