Prey availability

We examined the availability of benthic prey for YOY fishes caged around a municipal pier by coring the sediments around Pier 40 during the summers of 1998 and 1999 (June-July). Four replicate samples (3.0 cm diameter, 2.0 cm depth) were collected under, at the edge, and outside of the pier. Samples were returned to the laboratory where the contents were sorted, identified, and enumerated (see Duffy-Anderson and Able, 2001 for a complete description).

The benthos was dominated by nematodes and foraminifera (98 percent), though invertebrate eggs, polychaetes (capitellids and nereids), and copepods also made up a portion of the assemblage. Previous work indicated that nematoda and foraminifera did not make up a significant portion of the diet of YOY winter flounder, tautog, or Atlantic tomcod (Grabe, 1978; Klein-MacPhee, 1978; Sogard, 1992; Stehlik and Meise, 2000; Vivian et al., 2000; Metzger et al., 2001). As such, more appropriate estimates of prey availability for these fishes excluded nematodes and foraminifera from the analyses. Interestingly, when these two taxa were eliminated, significantly higher fish prey abundances were noted under the pier compared to outside in both years, though there were no significant differences in prey dry weight across the transect (Duffy-Anderson and Able, 2001). Previous findings at a nearby pier (Pier 76) in the lower Hudson River (Stoecker et al., 1992) found overall invertebrate abundances were higher under the pier than outside. It is currently not known if the apparent lower prey availability in open water is a function of grazing by perhaps, more abundant fishes, and higher availability under the pier is due to reduced grazing under piers caused by a depression in fish abundance. It is important to note that benthic prey appeared to be available in sufficient quantities for feeding of fish caged underneath municipal piers. Therefore, the hypothesis of limited prey availability under piers seemed an unlikely explanation for lower growth rates under piers as determined in the caging experiments. With this hypothesis eliminated, the issue of low light availability under piers seemed to take on even more significance.

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