Broadbill swordfish (Xiphias gladius) foraging and vertical movements in the north-west Atlantic.

The northern edge of Georges Bank is an important seasonal foraging habitat for swordfish (Xiphias gladius) in the North Atlantic, where aggregations support commercial pelagic longline and harpoon fisheries. Following a period of overfishing during the 1990s, the North Atlantic X. gladius stock underwent a period of recovery during the early 2000s and was considered rebuilt in 2009. We analysed stomach contents from X. gladius (n = 39) harvested by the Canadian harpoon fishery on Georges Bank in 2007 to characterize diet in this important foraging habitat. We used electronic tagging data from X. gladius (n = 6) on Georges Bank in 2005-2007 to assess vertical habitat preferences and associated prey composition within those zones. We also used stable isotope analysis (δ13 C and δ15 N) of X. gladius liver (n = 2) and common prey types (Paralepididae, Myctophidae, Merluccidae, Ommastrephidae) as a longer-term record of feeding. Stomach contents were co-dominated by Paralepididae [31.9% weight (W)] and Ommastrephidae (36.8%W) with secondary contributions from hake (Merluccidae, 6.5%W), Myctophidae (2.9%W) and Sebastidae (2.1%W). X. gladius displayed diel vertical migrations, descending to depths of 300-400 m during daytime followed by residence in surface waters at night. X. gladius liver δ15 N values were similar to or lower than values of primary stomach contents, likely due to bias of diet consumed in southerly waters with lower nitrogen isotope baselines prior to arrival on Georges Bank. Diet data are similar to results from historical studies from the late 1950s to the early 1980s. This apparent temporal stability to the underlying food web in this region may explain the high X. gladius site fidelity observed in electronic tagging studies and the consistent aggregation of these fish to this region.

Loss of gill rakers and teeth in adult specimens of barracudina Arctozenus risso (Aulopiformes: Paralepididae) from the western North Atlantic.

Two unusual adult specimens of the barracudina Arctozenus risso were caught in midwater trawls off the Flemish Cap in April 2016. These specimens displayed atypical traits including lack of teeth and gill rakers and fragile jaw bones; a combination of morphological examination and mtDNA sequencing confirmed species identification. Both specimens exhibited ripening ovaries and testes, confirming simultaneous hermaphroditism. These fish represent the first records of late-stage loss of features in the genus Arctozenus and may indicate a relationship to spawning in larger specimens.

Biodiversity and ecosystem function in the Gulf of Maine: pattern and role of zooplankton and pelagic nekton.

This paper forms part of a broader overview of biodiversity of marine life in the Gulf of Maine area (GoMA), facilitated by the GoMA Census of Marine Life program. It synthesizes current data on species diversity of zooplankton and pelagic nekton, including compilation of observed species and descriptions of seasonal, regional and cross-shelf diversity patterns. Zooplankton diversity in the GoMA is characterized by spatial differences in community composition among the neritic environment, the coastal shelf, and deep offshore waters. Copepod diversity increased with depth on the Scotian Shelf. On the coastal shelf of the western Gulf of Maine, the number of higher-level taxonomic groups declined with distance from shore, reflecting more nearshore meroplankton. Copepod diversity increased in late summer, and interdecadal diversity shifts were observed, including a period of higher diversity in the 1990s. Changes in species diversity were greatest on interannual scales, intermediate on seasonal scales, and smallest across regions, in contrast to abundance patterns, suggesting that zooplankton diversity may be a more sensitive indicator of ecosystem response to inter annual climate variation than zoo plankton abundance. Local factors such as bathymetry, proximity of the coast, and advection probably drive zooplankton and pelagic nekton diversity patterns in the GoMA, while ocean-basin scale diversity patterns probably contribute to the increase in diversity at the Scotian Shelf break, a zone of mixing between the cold-temperate community of the shelf and the warm-water community offshore. Pressing research needs include establishment of a comprehensive system for observing change in zooplankton and pelagic nekton diversity, enhanced observations of "underknown" but important functional components of the ecosystem, population and metapopulation studies, and development of analytical modeling tools to enhance understanding of diversity patterns and drivers. Ultimately, sustained observations and modeling analysis of biodiversity must be effectively communicated to managers and incorporated into ecosystem approaches for management of GoMA living marine resources.