Cetaceans are protected worldwide but vulnerable to incidental harm from an expanding array of human activities at sea. Managing potential hazards to these highly-mobile populations increasingly requires a detailed understanding of their seasonal distributions and habitats. Pursuant to the urgent need for this knowledge for the U.S. Atlantic and Gulf of Mexico, we integrated 23 years of aerial and shipboard cetacean surveys, linked them to environmental covariates obtained from remote sensing and ocean models, and built habitat-based density models for 26 species and 3 multi-species guilds using distance sampling methodology. In the Atlantic, for 11 well-known species, model predictions resembled seasonal movement patterns previously suggested in the literature. For these we produced monthly mean density maps. For lesser-known taxa, and in the Gulf of Mexico, where seasonal movements were less well described, we produced year-round mean density maps. The results revealed high regional differences in small delphinoid densities, confirmed the importance of the continental slope to large delphinoids and of canyons and seamounts to beaked and sperm whales, and quantified seasonal shifts in the densities of migratory baleen whales. The density maps, freely available online, are the first for these regions to be published in the peer-reviewed literature.

Trophic guild analysis identifies groups of species that use similar resources within a community. We evaluated the trophic guild structure in an assemblage of 40 fish species in the Northeast United States shelf ecosystem using a 25 yr database of food habits. We explicitly accounted for ontogenetic diet shifts by separating predator species into size classes. There were 14 significant trophic guilds. These distinguished predators based upon prey size and location in the water column (i.e., benthic to pelagic feeding). Ontogenetic diet shifts were important in guild structure, particularly within dominant piscivores. The mean dietary overlap both between and within guilds was notably lower than in other fish communities due to the broad spatial and temporal scale of the study, the diversity of prey types consumed, and the generalist nature of predators in this system. The guild concept is a useful framework to simplify highly connected, complex ecosystems like the Northeast US continental shelf and identify ecologically similar functional units.

Atlantic cod Gadus morhua is an extremely important fish in the northern hemisphere with respect to culture, economics, and ecology. However, the effects of over-fishing, environmental change, fish community dynamics and other factors that have altered the trophic ecology of cod are not well understood. We present an analysis of the trophic patterns of cod in the northeast US shelf ecosystem from a 25 yr time series of food habits data. Additionally, we compared the diet of this species with the spatio-temporal distribution of its prey species and evaluated prey preference over time. Atlantic cod exhibit an omnivorous diet; we assessed the temporal, spatial, and ontogenetic trends in this diet by examination of >15000 stomachs. Ontogenetic shifts in diet were observed; early juveniles consumed more pelagic than benthic invertebrates, medium cod consumed benthic invertebrates and fish, and larger cod consumed larger amounts of fish. Cannibalism also increased with ontogeny. Diet shifted significantly over a period of 3 decades, concurrent with changes in forage species abundance and distribution. Most of the major prey species were eaten in periods when they had high spatio-temporal overlap with cod and were abundant, indicating opportunistic feeding by cod. Similar to many other ecosystems, cod prefer sand lance, Cancer spp. crabs and herring, regardless of the abundance or spatio-temporal overlap with these prey species. It is unclear whether the observed changes in the trophic dynamics of cod have broad implications for cod populations, yet the evidence does suggest that cod are not likely to influence the abundance and distribution of their prey populations in this ecosystem.

Beaked whales are deep diving elusive animals, difficult to census with conventional visual surveys. Methods are presented for the density estimation of beaked whales, using passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period during and following the Deepwater Horizon oil spill (2010–2013). Beaked whale species detected include: Gervais’ (Mesoplodon europaeus), Cuvier’s (Ziphius cavirostris), Blainville’s (Mesoplodon densirostris) and an unknown species of Mesoplodon sp. (designated as Beaked Whale Gulf — BWG). For Gervais’ and Cuvier’s beaked whales, we estimated weekly animal density using two methods, one based on the number of echolocation clicks, and another based on the detection of animal groups during 5 min time-bins. Density estimates derived from these two methods were in good general agreement. At two sites in the western GOM, Gervais’ beaked whales were present throughout the monitoring period, but Cuvier’s beaked whales were present only seasonally, with periods of low density during the summer and higher density in the winter. At an eastern GOM site, both Gervais’ and Cuvier’s beaked whales had a high density throughout the monitoring period.