Differential growth and survival of weekly age-0 black crappie cohorts in a Florida lake

Black crappies Pomoxis nigromaculatus exhibit highly variable survival to a dulthood because of their varying larval and juvenile abundance, growth, an d mortality during early life. We examined how growth and mortality changed with hatch date, prey density, and water temperature for 7-d cohorts of ju venile black crappies in Lake Wauberg, Florida (a 150-ha hypereutrophic nat ural lake) during spring and summer 1998. Fish were collected once per week from March through June and twice per month during July and August by mean s of an otter trawl. Based on daily otolith rings, hatching occurred over a 12-week period (1 March-18 May). The mean daily growth rate (DGR) was posi tively related to water temperature, which increased over the hatching seas on. Common prey taxa included calanoid copepods, Daphnia and Bosmina spp., and cyclopoid copepods. The total density of these taxa did not differ sign ificantly among collection dates. Mean hatching date shifted from mid-March for fish collected in mid-April to early April for fish collected in late May. Early-hatched fish had lower DGRs (0.72 mm/d, compared with 0.76 mm/d for fish hatched in midseason and 0.82 mm/d for those hatched late in the s eason), higher mean daily instantaneous mortality rates (0.25, compared wit h 0.09 for the other two groups), and lower survival to the end of the firs t summer. As a result, the 1998 year-class of black crappies in Lake Wauber g was probably dominated by middle- and late-hatched individuals by the end of the first summer.