Stable isotope ratios in archived striped bass scales suggest changes in trophic structure

Abstract

Stable carbon isotope ratios were measured in archived striped bass, Morone saxatilis (Walbaum), scales to identify changes in the feeding behaviour of this species over time. Striped bass tissue and scale samples were collected from Rhode Island coastal waters during 1996 and archived scale samples (1982–1997) were obtained from Chesapeake Bay. Known striped bass prey items were also collected from Chesapeake Bay and analysed for δ13C. A significant correlation was observed between carbon isotope ratios in striped bass scales and muscle tissue (r2 = 0.52; P < 0.05). Carbon isotope ratios were enriched (less negative) in scales relative to muscle tissue by about 3‰. Carbon isotope ratios in archived striped bass scales from Chesapeake Bay increased significantly from −16.7 ± 0.2‰ in 1982 to −15.1 ± 0.3‰ in 1997. Benthic species, especially invertebrates, were isotopically enriched relative to pelagic fish species collected from the main-stem of Chesapeake Bay. Prey samples collected from riverine locations within Chesapeake Bay were isotopically depleted relative to those collected in the open portion of the Bay. The changes in the carbon isotope ratios of the striped bass scales could be related to changes in the relative proportions of pelagic and benthic food items in the diet of striped bass or to changes in the feeding locations of this species. In either case, there have been changes in the feeding behaviour and/or relationships of the striped bass between 1982 and 1997. Such changes may be related to changing ecological conditions within the estuary, which could influence the health of Chesapeake Bay striped bass.