Predation on post-settlement winter flounder Pseudopleuronectes americanus by sand shrimp Crangon septemspinosa in NW Atlantic estuaries

Abstract

Assessing predation risk is necessary to evaluate the functional significance of estuaries as critical nursery habitats for juvenile fishes. The objective of this study was to quantify rates of sand shrimp Crangon septemspinosa predation on post-settlement winter flounder Pseudopleuronectes americanus in 3 NW Atlantic estuaries: Narragansett Bay (Rhode Island), Niantic River (Connecticut), and Navesink River/Sandy Hook Bay (New Jersey). Sand shrimp were collected from designated study sites in late spring and summer (2001 and 2002), and their stomach contents were analyzed with immunological assays to detect the presence of juvenile winter flounder in the diet. The results indicate that sand shrimp are possible sources of intense predator-induced mortality for newly settled winter flounder. There was a direct relationship between the incidence of winter flounder in shrimp stomachs and the body size and density of shrimp. The importance of sand shrimp as a mortality fac- tor for winter flounder in the Navesink River/Sandy Hook Bay was minimal due to the low abundance of large shrimp (≥30 mm total length). Conversely, in Narragansett Bay and the Niantic River preda- tion rates were high because of the presence of large shrimp during peak winter flounder settlement periods (May to early June), when the flatfish are small in size and vulnerable to predation. Thus, sand shrimp predation rates on winter flounder depend on the relative spatial and temporal overlap between the settlement of flounder to the benthos and the movement patterns of large shrimp that migrate into shallow estuaries to reproduce and feed.