Recruitment Variability in Atlantic Menhaden: Processes Acting During the Larval-Juvenile Transition in Chesapeake Bay

Following two decades of high recruitments, Atlantic menhaden experienced historically low recruitments in Chesapeake Bay since the 1990s. Two underlying mechanisms were evaluated: 1) variability in larval ingress from the coastal ocean and 2) trophodynamic/environmental factors operating on young-of-the-year juveniles in the Bay. Abundance, hatch dates and growth rates of ingressing larvae were estimated from survey catches at the Bay mouth in 2005-2008. Recruitment levels of YOY juveniles from 1989-2004 were analyzed with respect to environmental variables. Annual abundance of larvae at ingress varied nine-fold, but levels were not concordant with subsequent juvenile abundance. Larval-stage and young-of-the-year juvenile growth varied inter-annually. Mean growth rate of ingressing larvae was fastest in 2007-08, the year of highest abundance. Most ingressing larvae hatched from October through December, but surviving juveniles had hatched primarily in January-February. Levels of young-of-the-year recruitments were strongly correlated with chlorophyll-a and primary productivity. A juvenile growth model, parameterized for temperature, chlorophyll-a, and year-class abundance accurately portrayed inter-annual and regional variability in growth. Climate variability acting on survival of eggs and larvae on the shelf, variable overwinter mortality of ingressed larvae, and variable primary production and predation acting on juveniles are believed to control recruitment levels in Chesapeake Bay.