Dynamics of zinc-65 specific activity and total zinc in benthic fishes on the outer continental shelf off Central Oregon

Abstract

The dynamics of 65Zn specific activity and total zinc in benthic fishes on the outer continental shelf off central Oregon (USA) were examined. A differential equation that relates specific activity of 65Zn in fish to that in fish food was used to estimate α's (zinc uptake-rate coefficients) for 3 different size classes of the flounder Lyopsetta exillis, a small predator of pelagic Crustacea, and for 1 size class of the flounder Microstromus pacificus, a large predator of infauna. The α's obtained for L. exilis were very close to the α obtained in the laboratory for the flounder Pleuronectes platessa. The α estimated for M. pacificus was very much smaller than the α's estimated for the other two species. A model that related α to predicted weight-specific feeding rates suggested that the smaller α of M. pacificus was caused by a low absorption efficiency of zinc from its prey. Sensitivity studies indicated that time histories of specific activity in the fishes are not sensitive to moderate changes in α. The negative correlation between specific activity in the diet and in the weight of L. exilis was the major cause of the negative correlative between specific activity and weight in this species. In M. pacificus, where composition of diet does not vary with size, specific activity was independent of weight. The time history of specific activity in M. pacificus was very much lower than those in the different size classes of L. exilis, a result caused mainly by the much lower specific activity of the prey of M. pacificus. Differences in specific activity among other benthic fishes were also correlated with differences in specific activity of their prey. The food-web dynamics responsible for these patterns are discussed. Variation in total zinc concentrations among species was small. Within species of flounder, zinc concentration varied only slightly or not at all with weight.