Spatial and temporal growth rate variation of bay anchovy (Anchoa mitchilli) larvae in the mid Hudson River estuary

Estuaries are critical habitats for larvae and juveniles of many marine fis hes, possibly because they promote high growth rates and survival rates. We investigated spatial and temporal changes in growth rate of larval bay anc hovy (Anchoa mitchilli), in the middle Hudson River estuary where abundance of larvae is high. In two consecutive summer seasons, we sampled larvae at 4 sites evenly spaced over 45 km, at weekly intervals for up to a month. W e examined otoliths to determine age in days and then used age-length regre ssions to estimate growth rate. In 1995, larval anchovy growth rates varied from 0.39 to 0.88 mm d(-1) (median = 0.48 mm d(-1)). In 1996, growth rates varied from 0.41 to 0.77 mm d(-1) (median = 0.55 mm d(-1)). In both years, we found significant spatial and temporal variation in growth rate. Larvae collected in the upper portion of Haverstraw Bay tended to grow more slowl y than larvae collected in other sites. The dates on which the most rapidly growing larvae were collected varied from site to site. Neither temperatur e nor salinity variations explained growth rate differences. Growth rate va riation, probably governed by patches of zooplankton, occurred on temporal scales of a week and spatial scales of 15 km.