The North Atlantic right whale (NARW), Eubalaena glacialis, feeds on zooplankton, particularly copepods of the genus Calanus. We quantified interannual variation in anomalies of abundance and biomass of Calanus spp. and near-surface and near-bottom ocean temperature and salinity from 19 subregions spanning the Gulf of Maine–Georges Bank (GoM–GBK), Scotian Shelf (SS), Gulf of St. Lawrence (GSL) and Newfoundland and Labrador Shelves. We analyzed time series from 1977 to 2016 in GoM–GBK, 1982 to 2016 in southwest GSL and 1999 to 2016 in remaining areas. Calanus finmarchicus dominated abundance and biomass, except in the GSL where Calanus hyperboreus was abundant. The biomass of Calanus spp. declined in many subregions over years 1999–2016 and was negatively correlated with sea surface temperature in GoM–GBK and on the SS. We detected ``regime shifts” to lower biomass of Calanus spp. in the GoM–GBK in 2010 and on the SS in 2011. In the GoM–GBK, shifts to lower biomass of C. finmarchicus coincided with shifts to warmer ocean temperature and with published reports of changes in spatial distribution and reduced calving rate of NARW. We hypothesize that warming has negatively impacted population levels of Calanus spp. near their southern range limit, reducing the availability of prey to NARW.
Changes in the physical oceanography of the Northwest Atlantic stemming from both natural and anthropogenic climate change impact the foraging ecology and distribution of endangered North Atlantic right whales. In this study, right whale sightings from 1990 to 2018 were analyzed to examine decadal patterns in monthly habitat use in 12 high-use areas. Depth-integrated abundances of late-stage Calanus finmarchicus and Calanus hyperboreus were also analyzed for decadal variations in the right whale foraging habitats. There were significant differences in the occurrence, seasonal timing, and persistence of foraging habitats across these three decades. In the decades of the 1990s and the 2010s, prey was less abundant than in the 2000s, corresponding to reduced use of the Southeast US calving grounds in the winter, increased use of Cape Cod Bay in winter and spring, and reduced use of Roseway Basin in the fall. In the 2010s, right whale sightings increased in Southern New England and the Gulf of St. Lawrence in the spring and summer, respectively. Summertime declines in the 2010s in late-stage copepod abundances in the Gulf of Maine and surrounding regions, as well as in the Gulf of St. Lawrence, indicate that recent increased use of the Gulf of St. Lawrence is driven by a decline in prey in traditional foraging habitats rather than by an increase in prey in the new foraging habitat. This analysis of decadal-scale differences in right whale sightings and prey abundance is critical for redefining right whale distribution patterns for the most recent (post-2010) decade.
The North Atlantic right whale (NARW), Eubalaena glacialis, resides primarily on western North Atlantic continental shelves where this endangered species is susceptible to vessel strike and entanglement in fishing gear. Mitigation of these threats is dependent on the ability to predict variations in NARW occurrence. North of the Mid-Atlantic Bight, the distribution of NARWs is influenced by their prey, mainly copepods of the genus Calanus. We review factors that promote suitable foraging habitat from areas where NARWs have been observed feeding. We then synthesize our findings within a conceptual framework in which availability (i.e. shallow prey depth), supply, and aggregation of prey occur together to facilitate suitable foraging habitat. By definition, the depth of prey on the shelf is constrained to ≤200 m and other mechanisms may occur locally that further enhance prey availability. Enhanced production of prey occurs in coastal currents, which transport the copepods to NARW foraging areas. Prey concentrating mechanisms are not well-characterized. Information gaps that impede rapid and dynamic prediction of suitable foraging habitat include limited data on the spatial and temporal variation of prey and environmental conditions at local scales (i.e. 0.1–1 km), motility of prey, and diving behaviour of NARWs.
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