Regional and temporal variability in growth and mortality of bay anchovy, Anchoa mitchilli, larvae in Chesapeake Bay

Temporal and spatial variability in growth and mortality rates of bay ancho vy, Anchoa mitchilli, larvae was analyzed in Chesapeake Bay. Larvae were co llected in cruises during June and July 1993, on transects spaced at 18.5-k m (10 nmi) intervals over the entire bay. Growth and mortality rates were e stimated in lower, mid, and upper bay regions and analyzed in relation to e nvironmental variables, predators (biovolumes of the scyphomedusa Chrysaora quinquecirrha and the ctenophore Mnemiopsis leidyi), and larval prey (zoop lankton abundances). Otolith increment analysis indicated that the mean bay wide growth rate of larvae increased significantly from 0.59 mm/d in June t o 0.72 mm/d in July. The baywide mortality rate of larvae declined from 0.4 1 (33.6%/d) in June to 0.23 (20.5%/d) in July. In each month, regional mort ality rates were highest in the lower bay. Regionally, mortality ranged fro m a low of 0.14 (13.1%/d)in the upper bay in July to a high of 0.54 (41.7%/ d) in the lower bay in June. Mortality rates declined with increasing larva l size. Stage-specific survival was both size-specific and growth-rate depe ndent as indicated by trends in mortality (M), weight-specific growth (G), and the MIG ratio. Growth rates were positively correlated with temperature and zooplankton abundance. Larval abundances, but not mortality rates, wer e negatively correlated with gelatinous predator biovolumes. Recruitment po tential of bay anchovy was judged to be highest in July in the lower third of Chesapeake Bay. Although lower, production of anchovy prerecruits in Jun e and in other Bay regions was substantial and contributed significantly to prerecruit abundances in 1993.