Interannual and Regional Patterns of Abundance, Growth, and Feeding Ecology of Larval Bay Anchovy (Anchoa Mitchilli) in Chesapeake Bay

Abstract

Patterns in abundance, growth , and feeding by larval bay anchovy were examined in Chesapeake Bay from 1995-1999 to evaluate factors that contribute to variable recruitments of this abundant fish. The patterns were examined in relation to environmental factors, including hydrography and distributions of prey (zooplankton) and a probable predator (ctenophore). Larval abundances, sizes, feeding incidences, and growth rates varied annually and regionally. Averaged over five years, mean abundances in July decreased by almost two orders of magnitude from the mouth (38.l/m2) to the head (0.6/m) of the Bay, a long a declining salinity gradient. Yearly survey, bay-wide mean abundance varied nearly 10-fold; it was highest in 1998 (42. 7 /m2) and lowest in 1996 (4.6/m2). Feeding incidence was highest in 1998 (23%) and lowest in 1996 (9%), and varied regionally from 27% in the upper Bay to 13% in the mid Bay. Larvae fed predominantly during daylight. The most common prey ingested were copepod eggs and various life stages of calanoid copepods (primarily Acarlia Lonsa). Growth rates of larvae also differed annually and regionally. Mean growth rate was highest in 1998 (0.81 mm/d) and lowest in 1999 (0.68 mm/d), and varied regionally from 0.83 mm/d in the upper Bay to 0.71 mm/din the mid Bay. Zooplankton concentration was positively correlated with larval feeding incidence (r = +0.66) and growth rate (r = +0. 72). Larval feeding incidence was strongly correlated (r = +0.93) and summer larval abundance significantly correlated (r = +0.86) with fall recruitment of young-of-the-year bay anchovy.