PREDATION BY SEVENSPINE BAY SHRIMP CRANGON SEPTEMSPINOSA ON WINTER FLOUNDER PLEURONECTES-AMERICANUS DURING SETTLEMENT - LABORATORY OBSERVATIONS

In laboratory experiments, we determined the relative amount of predation before, during and after settlement with winter flounder Pleuronectes americanus as prey and sevenspine bay shrimp Crangon septemspinosa as predators. Wild-caught winter flounder at various stages of morphological development and settlement [from presettled, pre-eye-migration (less than or equal to 11 mm standard length, SL) to eyes fully migrated, settled individuals (10.0 to 34.3 mm SL)] were exposed to predation by adult shrimp (47 to 74 mm total length). Mortality in treatments involving small settled flounder (78%) was twice that of presettled individuals (30 to 45%). However, subsequent mortality decreased with flounder size, and was 0% for flounder greater than or equal to 20 mm SL. Predator density affected rate of predation on settled juveniles (8.7 to 19 mm SL); mortality increased from 0 to 80% as predator density increased from 0 to 10.6 m(-2). At den sities greater than or equal to 10.6 m(-2), mortality reached an upper asymptote of 80 to 90%. These experiments suggest that predation by shrimp may be an important determining factor of habitat selection, size and mortality during settlement of winter flounder and other benthic fishes.