Ecological Interactions between Elasmobranchs and Groundfish Species on the Northeastern U.S. Continental Shelf. I. Evaluating Predation

Abstract

Elasmobranchs are an important component of the northeastern U.S. continental shelf ecosystem in terms of both biomass and abundance. It has been hypothesized that because of their high biomass these species have a significant negative impact on commercially valuable groundfish via ecological interactions. One of these hypotheses posits that elasmobranchs directly remove such groundfish by predation. We analyzed data from the stomachs of 40,756 spiny dogfish Squalus acanthias, 3,806 smooth dogfish Mustelus canis, 17,618 little skate Raja erinacea, 11,593 winter skate R. ocellata, and 2,571 thorny skate R. radiata collected in bottom trawl surveys conducted principally during spring and autumn 1973–1998 in waters from Cape Hatteras, North Carolina, to Nova Scotia. Except for silver hake Merluccius bilinearis, most groundfish are not common in the diets of the elasmobranchs. Estimates of consumption indicate that both the number and the total biomass of the groundfish that are removed are generally small fractions of total fishery removals and stock sizes. The number of potential recruits removed could be high, but there is no relationship between recruitment success and elasmobranch abundance. We conclude that predation by elasmobranchs probably does not have significant impacts on groundfish in this system and list alternative causal mechanisms for the observed changes in this fish community.