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.

Stock abundance was the most important predictor of sexual maturation of age 2 and 3 silver hake in the north‐west Atlantic between 1973–1990. Growth at ages 1 and 2 in the southern stock was significantly and negatively correlated with stock abundance (r2>0.56, P<0.01). Sexual maturity may be mediated through competition and growth during the first and second years of life. In the northern stock, growth and stock abundance was not significantly correlated (P>0.05). Here, increased sexual maturity at ages 2 and 3 during 1973–1990 may have occurred without increased somatic growth, already near its maximum, due to the relatively cooler water temperatures of the Gulf of Maine. Logistic regression models indicated that maturation is dependent on age, stock density and an age‐density interaction.

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The meso-scale trophic dynamics of cod Gadus morhua were examined based upon tri-monthly stomach sample collections from a nearshore, localized (c. 800 km 2 ) region off Cape Cod, Massachusetts, U.S.A. The major objective for this work was to relate any changes in cod diet and amount of food eaten to seasonal variations in prey availability, water temperature and spawning at a spatial scale between broad-scale and laboratory studies. Results suggested that the type and amount of food eaten by cod was generally consistent throughout a year and repeatable across years. Cod feeding was marked by two periods of increased feeding, corresponding to the arrival of small pelagic fishes in the area. This pelagic migration and subsequent increased feeding by cod occurred during important periods in the life history of cod (e.g. spawning and overwintering). Similar annual patterns in food consumption and diet composition were remarkably consistent over the 2Á5 years of the project, suggesting important feeding periods for cod that correspond to environmental and biological events. The diet of cod was composed primarily of several species of forage fishes [e.g. herrings (predominantly Atlantic herring Clupea harengus), sand lance Ammodytes sp. and Atlantic mackerel Scomber scombrus], ophiuroids, Cancer sp. crabs and other small crustaceans. It was inferred that cod exhibited a maintenance diet on local forage fishes and benthic macroinvertebrates, augmenting their diet by seasonally gorge feeding upon migrating pelagic species.Journal compilation # 2007 The Fisheries Society of the British Isles No claim to original US government works