Diel and tidal influences on the abundance and food habits of four young-of-the-year fish in Delaware Bay, USA, marsh creeks

Diel and tidal studies are critical to understanding many aspects of fish behavior and habitat use. In this study, diel and tidal abundance, size composition and food habits of four common juvenile fish (Anchoa mitchilli, Cynoscion regalis, Leiostomus xanthurus, Micropogonias undulatus) present in Delaware Bay (USA) marsh creeks was assessed. Fish were collected with otter trawls near daytime and nighttime high tides and with seines near daytime and nighttime low tides at two mesohaline sites. Anchoa mitchilli and C. regalis were both significantly more abundant and significantly smaller in nighttime samples. Micropogonius undulatus was the most abundant species, while A. mitchilli was entirely absent, in low tide collections. An index of stomach fullness for A. mitchilli and L. xanthurus indicated feeding during periods of maximum flooding. Trophic interactions among the four species were also apparent. Both C. regalis and M. undulatus commonly consumed A. mitchilli only during nighttime high tides. Cynoscion regalis and M. undulatus both consumed large quantities of Fundulus heteroclitus (mummichog) during low tides during both the day and night. This important interaction demonstrates the trophic transfer of production in the marsh (F. heteroclitus) to the open ocean via the fall migration of piscivorous M. undulatus. These findings demonstrate the need for diel and tidal sampling programs if we are to adequately understand the dynamics of marsh ecosystems.