North Atlantic right whale (Eubalaena glacialis) and its food: (II) interannual variations in biomass of Calanus spp. on western North Atlantic shelves

Abstract

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.

Foraging habitat of North Atlantic right whales has declined in the Gulf of St. Lawrence, Canada, and may be insufficient for successful reproduction

“…Therefore, there is no clear indication that feeding conditions notably improved for right whales in the Gulf of St. Lawrence in the later years of our study, although they may have been better than in other foraging habitats. This aligns with the observation that C. fin- marchicus and C. hyperboreus biomass has de creased everywhere in the Gulf of Maine and eastern Canadian shelf waters since around 2010, whereas their biomass remained higher on average in the Gulf of St. Lawrence than in other feeding areas of North Atlantic right whales over the period 1979− 2016 (Sorochan et al 2019).…”

“…The methodology for depth-integrated zooplankton sampling and abundance assessment (ind. m −2 ) for the 3 dominant Calanus copepod species (C. finmarchicus, C. glacialis and C. hyperboreus) was summarized by Plourde et al (2019) and Sorochan et al (2019). Briefly, samples were collected with oblique or vertical tows respectively performed with Bongo nets (opening 0.61 m; mesh size 333 μm) or ring nets (opening 0.75 m; mesh size 200 μm).…”

“…The copepod biomass in the Gulf of St. Lawrence is predominantly C. hyperboreus (Sorochan et al 2019), a species of unknown dietary contribution to right whales. This species declined in abundance from 2006 to 2017 in the southern Gulf of St. Lawrence and largely drove our conclusion that right whale habitat quality declined over time.…”

Exploring movement patterns and changing distributions of baleen whales in the western North Atlantic using a decade of passive acoustic data

“…Lastly, on a more regional scale, a significant shift in habitat use after 2010 can be seen in the decreased acoustic occurrence of humpback, fin, blue, and NARWs on the Scotian Shelf (region 3). What might be driving this shift remains unclear; it is possible the shift reflects changes in prey availability similar to that observed in the Gulf of Maine (Sorochan et al., 2019), but there is little data to elucidate this process. Nevertheless, the data suggest that the Scotian Shelf (region 3) has become a less preferred habitat for most baleen whales since 2010.…”

“…What might be driving this shift remains unclear; it is possible the shift reflects changes in prey availability similar to that observed in the Gulf of Maine (Sorochan et al, 2019), but there is little data to elucidate this process. Nevertheless, the data suggest that the Scotian Shelf (region 3) has become a less preferred habitat for most baleen whales since 2010.…”