If certain species are better able to forage under piers than others, that ability should be reflected as a difference in growth rate. Therefore, we designed a series of experiments to determine differences in growth rates between fishes more frequently collected under piers and those that were infrequently found in under-pier habitats. We hypothesized that species collected under piers would have higher growth rates in under-pier habitats than species that occurred there less often. These studies would not only reveal more about differences in pier habitat use among fishes, but they would also provide a more quantitative measure of pier habitat quality (Level 3) that could augment our initial observations.
Based on abundances estimated from the trapping experiments, we chose two fish species that were uncommon in our under-pier collections, winter flounder and tautog, and one species that was collected from beneath piers more regularly, the Atlantic tomcod, as our target species for growth experiments. Young-of-the-year fish of a single species were confined to benthic cages deployed to open water, pile fields, under piers, and at pier edges for ten day periods and changes in fish weight (that is, growth rate in weight) were determined. Randomly chosen specimens also servedas controls, which were kept in the laboratory for ten days without food. Growth experiments occurred in 1994,1996,1997, and 1998 (see Duffy-Anderson and Able, 1999; Able et al., 1999; and Metzger, Duffy-Anderson, andAble, 2001 for more complete descriptions).
As a result of these experiments over four years, we observed variations in growth rate among habitat types and between the three test species. Young-of-the-year winter flounder had negative growth rates (that is, they experienced weight loss) when they were caged under piers, indicating that the fish had fed poorly (Fig. 29.3). In fact, weight loss under piers was strikingly similar to weight loss among control individuals, the fish that were intentionally starvedinthe laboratoryfor ten day periods. In contrast, winter flounder grew well in open water habitats adjacent to piers and in pile fields. Individuals also grew at pier edges but rates in that habitat were generally lower than in pile fields or open water (approximately 40 percent less).
Growth rates among caged YOY tautog followed similar patterns, though variability was somewhat higher (Fig. 29.3). Tautog caged under piers also lost weight at rates comparable to laboratory-starved control fish. In contrast, tautog caged at pier edges, in pile fields, and in open water grew rapidly with several individuals actually doubling their body weight over the course of the ten day experiments.
Results with Atlantic tomcod yielded somewhat different results. In contrast to the YOY winter flounder and tautog, two species that lost weight under piers, YOY Atlantic tomcod gained weight when caged in under-pier habitats, though weight gain under piers was not as rapid as weight gain at edges or in open water (Fig. 29.3). In fact, though growth under the pier was positive, it occurred at nearly half the rate as growth at pier edges or outside of the pier, a substantial discrepancy that could have important impacts on the overall recruitment success of juveniles to the adult population (Sogard, 1997; Beck et al., 2001).
The general outcome of the growth experiments followed hypothesized patterns. Fishes that were more frequently collected from under piers should be better able to utilize those habitats than fishes
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