Transport and retention of fish early-life stages in Chesapeake Bay: Mechanisms and implications for recruitment

Mechanisms of transport and retention of fish eggs and larvae that result from small-scale biological-physical interactions are described for three species of estuarine-spawning fish: bay anchovy (Anchoa mitchilli), white perch (Morone americana), and striped bass (M. saxatilis) in Chesapeake Bay.; Research on bay anchovy early-life stages identified factors that influenced their small-scale distribution and potential transport. Depth-stratified sampling at a fixed station demonstrated that the pycnocline was an important physical feature structuring the planktonic community. Most bay anchovy early-life stages, copepods (prey) and ctenophores (predators) occurred above it. Variations in organism abundances were associated with the advection of water masses past the fixed station. Variable wind-forced circulation patterns, below-pycnocline dissolved oxygen concentrations, ontogenetic and diel changes in larval swimbladder inflation, and diel changes in vertical distribution of larvae in relation to copepod prey have important consequences for potential transport of bay anchovy larvae.; Results on white perch and striped bass demonstrated the importance of the estuarine turbidity maximum (ETM) region as a nursery area. Surveys of the upper bay and fixed-station sampling within the ETM were conducted in May 1998 (three cruises) and May 1999 (two cruises). In high-flow conditions (1998), fish early-life stages were abundant and concentrated in the ETM region that overlapped the salt front. Fish eggs, yolk-sac larvae and Eurytemora affinis copepods appeared to be retained passively in the convergence zone within the salt front and ETM. Feeding-stage larvae probably accumulated in the ETM by tracking their passively retained prey (copepods). In low-flow conditions (1999), feeding-stage larvae were significantly less abundant and the salt front was up-estuary of the ETM. Freshwater flow was positively correlated with juvenile recruitments (1968/1977–1999) and explained a large portion of variability in spawner-recruit relationships (1987–1999). The close coupling between physical conditions, larval concentrations and prey distributions between cruises and years suggested that annual differences in freshwater flow influence larval retention, survival and recruitment by controlling the physical-biological characteristics of the ETM region. Differences in life-history strategies, tradeoffs between optimal zones of feeding success or retention in the ETM, and episodic wind/flow events modulate the relationship between larval survival and freshwater flow.