Impacts of Piers on Juvenile Fishes in the Lower Hudson River

Kenneth W. Able and Janet T. Duffy-Anderson abstract We examined the impacts of man-made structures, especially large piers, on fishes in the lower Hudson River, USA over a number of years. We used a multifaceted approach, and evaluated: 1) the distribution and abundance of fishes under piers, at pier edges, in pile fields, and in open water areas, 2) feeding and growth of young-of-the-year fishes (winter flounder, tautog, and Atlantic tomcod) under and around piers, and 3) availability of benthic prey for fishes under and adjacent to large piers. A review of our studies suggests that species diversity and species abundance were depressed under piers relative to nearby habitats. The only species that were routinely collected from under piers were those that do not appear to solely rely on the use of vision to forage (American eel, naked goby, Atlantic tomcod). Results from studies of the distribution of benthic invertebrate prey for fishes around piers suggest that prey abundances under piers are more than sufficient to support fish growth, however, results of directed growth studies indicate that feeding and growth rates of visually-feeding fish species (winter flounder, tautog) are negative under piers (that is, fish lose weight). It is not likely that factors associated with pier pilings, such as reduced flow or sedimentation, affect feeding, since studies of fish growth in pile fields (piers without the decking) indicate that fish grow well in that habitat. Rather, it appears that the decking associated with piers creates conditions of intense shading that impede foraging activities. We propose that under-pier areas, and potentially any areas that significantly reduce light penetration to depth in near shore areas, are poor habitats for fishes, and we urge careful consideration of shading effects prior to the construction, restoration, or renovation of overwater structures.

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