No abstract

Abstract-Diel sampling was conducted during June-September 2013, in the shore zone and adjacent nearshore zone of Delaware Bay, Delaware, to identify day and night changes in nekton density, species richness, and the species assemblage. Mean species richness and total nekton density in the shore zone were higher at night. A detailed examination of abundant species revealed that bay anchovy (Anchoa mitchilli), weakfish (Cynoscion regalis), spot (Leiostomus xanthurus), and blue crab (Callinectes sapidus) occurred in higher densities in the shore zone at night than during the day. Bluefish (Pomatomus saltatrix) occurred in higher densities during the day. Additionally, small (<20 mm in fork length) Atlantic silverside (Menidia menidia) and bay anchovy, were observed in abundance in the shore zone only during daytime. Day and night differences in predatorprey dynamics were likely a primary driver of diel differences in nekton abundances observed in the shore zone. No diel differences in species richness, nekton density, or species assemblage were found in the adjacent nearshore area. Daytime sampling predominates in studies of shore-zone nekton and our results show the value of also sampling at night. Future research should include samples throughout the diel cycle and include tagging and movement data to allow a better understanding of diel dynamics of nekton along sandy beach shores.

We conducted a mark–recapture study over a 98‐d period from June 20 through September 26, 2013, in lower Delaware Bay, USA, to examine movement and site fidelity of the Atlantic Croaker Micropogonias undulatus and Spot Leiostomus xanthurus. A secondary objective was to evaluate the effectiveness of visible implant elastomer (VIE) tagging for these species. Fish were tagged at five shore‐zone sites along approximately 5 km of gradually sloping sandy beach and at a site along 300 m of riprap‐hardened shoreline. Additional tagging occurred in an adjacent area (~36 ha) of nearshore habitat. Atlantic Croakers and Spot (15 individuals per species) were also tagged and held in the laboratory for 2 months to examine tag retention and fish survival. In total, 133 Atlantic Croakers and 253 Spot were tagged and released. The VIE tagging was shown to be a highly effective technique for studying the movement of these species; tag retention rates were 100% and 98% in Atlantic Croakers and Spot, respectively, and no mortality was observed among tagged fish held in the laboratory. No tagged fish were recaptured in shore‐zone or nearshore sampling, indicating a lack of site fidelity by either species in these habitats. These results demonstrate the need for more extensive research on the movements of shore‐zone nekton in the U.S. mid‐Atlantic region.