Effects of municipal piers on the growth of juvenile fishes in the Hudson River estuary: a study across a pier edge

The growth rates of two fish species, the winter flounder Pseudopleuronecte s americanus (Walbaum) (19.3 to 42.6 mm total length, TL) and the tautog Ta utoga onitis (Linnaeus) (23.9 to 55.9 mm TL), were used to evaluate habitat quality under and around municipal piers in the Hudson River estuary, USA. Growth rates were measured in a series of 10 d field caging-experiments co nducted at two large piers in the summers of 1996 and 1997. Cages (0.64 m(2 )) were deployed along transects that stretched from underneath the piers t o beyond them, encompassing the pier edge (the transitional zone between th e pier interior and the outside). Growth in weight (G(w)) was determined at five locations along the transect, 40 m beneath the pier, 20 m beneath the pier, at the pier edge, 20 m beyond the pier edge, and 10 m beyond. Under piers, mean growth rates of winter flounder and tautogs were negative ((x) over bar G(W) = -0.02 d(-1)), and rates were comparable to laboratory-starv ed control fishes ((x) over bar G(W) = -0.02 d(-1)). In contrast, mean grow th rates at pier edges and in open waters beyond piers were generally posit ive ((x) over bar GW ranged from -0.001 to + 0.05 d(-1)), with growth at pi er edges often being more variable and less rapid than at open-water sites. Analyses of stomach contents upon retrieval of caged fishes revealed that dry weights of food were generally higher among fishes caged at open-water stations ((x) over bar range = 0.02 to 0.72 mg dry wt) than at pier-edge (( x) over bar range = 0.01 to 0.54 mg) or under-pier ((x) over bar range = 0. 03 to 0.11 mg) stations, although it was apparent that benthic prey were av ailable at all stations on the transect. Our results indicate poor feeding conditions among fishes caged under piers, and suboptimal foraging among fi shes caged at pier edges. Inadequate growth rates can lead to higher rates of mortality, and, based on these and other earlier experiments, we conclud e that under-pier environments are poor-quality habitats for some species o f juvenile fishes.