Discussion

The potential value of man-made structures as habitats for fishes is of considerable interest and may be especially relevant in urban estuaries like New York Harbor where little natural habitat remains in shallow, nearshore waters. We have shown that at least one type ofman-made structure, large piers, do not afford suitable habitat to a number of fish species in the lower Hudson River. This conclusion is based on three of the four levels of habitat evaluation, distribution (Level 1), abundance (Level 2), and feeding and growth (Level 3), as previously outlined (Schreiber and Gill, 1995;Able, 1999; Minello, 1999). We conclude that under-pier areas are poor-quality habitats because they support low fish abundances, inhibit feeding, and suppress growth. We believe that low light levels under piers (as measured over several years of study) are directly related to their lower habitat value relative to other areas (Table 29.1) and several lines of evidence support this view. First, the few species that are more commonly collected from beneath piers (American eels, Atlantic tomcod, naked goby, decapod crustaceans) share an ability to capitalize on sensory systems other than vision (chemorecep-tion, mechanoreception) to locate prey in conditions of near-darkness. Visually feeding fishes generally do not occur under piers, probably because the low-light conditions there interfere with their ability to feed. Second, two fish species that use visual foraging mechanisms, winter flounder and tautog, show reductions in food intake and poor growth under piers, in spite of having more than sufficient numbers of prey available for consumption. Third, these same two species of fish grow

Table 29.1. Habitat values of pier-related habitats in the lower Hudson River based on estimates of distribution, abundance, feeding, and growth of young-of-the-year fishes in New York Harbor

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