Spatial patterns in diet and distribution of juveniles of four fish species in Delaware Bay marsh creeks: factors influencing fish abundance

Abstract

Delaware Bay is one of the largest estuaries on the east coast of the United States and provides juvenile habitat for many fish species. We investigated spatial patterns in the diet and dis- tribution of the young-of-the-year of 3 marine transients — the weakfish Cynoscion regalis, the spot Leiostomus xanthurus and the Atlantic croaker Micropogonias undulatus — and the juveniles and adults of 1 estuarine resident, the white perch Morone americana, in 5 marsh creeks systems along a salinity gradient running from the poly/mesohaline (12 to 20) lower bay to the meso/oligohaline upper bay (0 to 12). Sampling was conducted monthly from April through November in 1997 and 1998, resulting in over 1700 otter trawl (4.9 m, 6 mm cod-end mesh) samples and 5703 fish stomachs examined, making this one of the largest studies of its kind. We employed a bootstrap technique to generate 95% confidence intervals for proportional consumption of the major prey categories. The diets of the target species differed significantly among the 5 marsh creeks. Mysid consumption was high for all species at the 3 most saline marshes and low at the 2 freshest sites, suggesting either low mysid abundance or availability at the latter sites. Consumption of insect larvae was important only at the freshest site. L. xanthurus consumed 80% annelids at the most saline sites, but less that 32% at the other sites. The other important consumer of annelids, Micropogonias undulatus, consumed similar quantities of annelids at all sites (32 to 41%). Total stomach fullness was almost always higher at the sites of highest fish abundance. We conclude that the marine transients appear to recruit pre- ferentially to sites of high resource abundance, while M. americana is restricted by physico-chemical tolerance during the spring through fall to limited juvenile habitats where it may experience food resource competition.