ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01376

ABSTRACT: Declines and shifts in the distribution of the critically endangered North Atlantic right whale Eubalaena glacialis since 2010 have underscored the need to better understand drivers of right whale habitat use. The influence of Calanus finmarchicus prey on right whale distribution is well established, but less is known about the relative importance of other prey taxa, especially in habitats south of the Gulf of Maine (GOM). We used data from NOAA’s Ecosystem Monitoring Program (1980–2019) to assess spatiotemporal changes in the abundance of copepod prey and implications for right whale foraging energetics. Decadal-scale changes in copepods were most pronounced in the GOM, led by a marked summer increase of the copepod Centropages typicus. Spatiotemporal changes in right whale habitat use generally followed the estimated energy content of regional prey fields, driven mainly by the abundance of C. finmarchicus, which has an energy density approximately 10 times that of C. typicus. Increases in the abundance of smaller copepods in the GOM since 2010 have been insufficient to compensate energetically for the decline in C. finmarchicus in the eastern GOM in summer, where observations of foraging right whales have declined sharply. In southern New England, a site of increased right whale observations, the winter energy content of the sampled prey field was higher than other subregions. Our analysis highlights that further ocean warming, predicted to negatively impact C. finmarchicus and positively impact smaller copepods, may influence whether traditional foraging grounds can support large numbers of foraging right whales.