Assessing the quality of four inshore habitats used by post yolk‐sac Alosa sapidissima (Wilson 1811) in the Hudson River: a prelude to restoration

Habitat restoration within large rivers to enhance early life stages of fish is an emerging field. Prior to restoration, assessment of what constitutes good habitat is needed. We exemplify this with a study of larval Alosa sapidissima (American shad) in the Hudson River estuary in New York State, United States, which examines the quality of four main shallow water habitat types that have been reduced greatly by dredging activities. The larval stage has been identified as a sensitive period in need of mortality reduction. Habitats were examined as nursery habitat by comparing ambient conditions to known suitability indexes and by comparing relative abundance, loss rate, daily growth, and relative condition among habitats. Areas of lower velocity had greater abundances of shad 15.0 mm in length and shad growth was significantly higher. As shad became larger, those in areas of higher velocity had significantly higher relative condition, suggesting a shift in habitat use as larvae metamorphose into the juvenile stage. Contiguous backwater and secondary channel habitats had reduced loss rates during 2011 when there was high river discharge. No single habitat type examined in this study was found to be overall poor quality, and it is recommended that restoration sites be examined on an individual basis. More broadly, habitat diversity appears needed both for within-year ontogeny as well as for longer-term resiliency in the face of disturbance, such as storm-driven high flows.