TROPHIC RESOURCE PARTITIONING, DIETS, AND GROWTH OF SYMPATRIC ESTUARINE PREDATORS

Striped bass Morone saxatilis, bluefish Pomatomus saltatrix, and weakf ish Cynoscion regalis are the dominant piscivores in the Chesapeake Ba y. As such, they may influence energy flow in the Chesapeake Bay syste m according to the prey they Eat and the trophic levels at which they feed. We defined and compared the diets of striped bass, bluefish, and weakfish from the Chesapeake Bay, across seasons and early ages. Seas onal weight changes of the predators were used to evaluate how differe nt prey species contribute to the production of average individual pis civores. Dietary overlap among species and across cohorts within a spe cies was low (24-51% bimonthly average range, Schoener's index). Bluef ish often had higher dietary overlap values with striped bass and weak fish than with other bluefish cohorts. Dietary overlap between striped bass and weakfish cohorts was usually low because of disparity in the use of bay anchovies Anchoa mitchilli by striped bass (<31% in all mo nths) and weakfish (>50% for most age-0 and age-1 weakfish). Overall, pelagic prey fishes dominated the diets of all predators except age-0 striped bass, although seasonal differences were evident. During May-J une, nearly all predator cohorts fed on benthic prey. In general, the Atlantic menhaden Brevoortia tyrannus and the bay anchovy supported mo st of the piscivore production, with Atlantic menhaden becoming increa singly important for larger predators. Benthic prey were more importan t to striped bass (from nearly 100% of diets for age-0 fish in all sea sons to 20-100% for older striped bass) and less important to bluefish (70% in July-August, 1-20% at other limes and for other cohorts) than was suggested in an earlier food web analysis for the Chesapeake Bay ecosystem.