Estimates of Prey Consumption and Trophic Impacts of Cetaceans in the USA Northeast Continental Shelf Ecosystem

Whales, dolphins and porpoises are significant consumers of prey resources in the USA Northeast Shelf marine ecosystem to a far greater extent than was realized two decades ago. Seasonal estimates of the consumption of finfish, squid and zooplankton by cetaceans were calculated for four regions of the Northeast Shelf system defined as Gulf of Maine, Georges Bank, Southern New England and Mid-Atlantic Bight. Estimates were based on seasonal cetacean abundance using standard mammalian metabolic models scaled as appropriate for assimilation, activity and migratory fasting. Estimates were made of mean body mass and proportion of the diet comprised of each of the three main prey types. Cetaceans of the Northeast Shelf were found to consume nearly 1.9 million tons annually, including about 1.3 million tons of fish, 337 000 tons of squid and 244 000 tons of zooplankton. Their predation on fish and squid exceeded tonnages harvested in the commercial fishing industry. Consumption estimates of fish dominated in most regions and seasons, primarily because of the widespread distribution and high relative abundance of large piscivorous fin whales, and secondarily due to the presence of humpback and minke whales and some of the smaller odontocetes. Zooplankton consumption, principally by right and sei whales and secondarily by other mysticetes, was significant in some seasons in the Gulf of Maine and Georges Bank regions. An assemblage which included a variety of teuthivorous odontocete species inhabiting the shelf break vicinity consumed substantial quantities of squid in all regions except the Gulf of Maine. Using a simple five-level trophic model and 10% estimated trophic transfer efficiency, the estimates implied that a significant fraction of the total net primary production, ranging from 11.7% in the Mid-Atlantic Bight to 20.4% in the Gulf of Maine, was required to the support cetacean apex predation.