North Atlantic right whale Eubalaena glacialis prey selection in Cape Cod Bay

Abstract

North Atlantic right whales Eubalaena glacialis have been observed feeding in Cape Cod Bay (CCB) for over 8 decades, making CCB the most consistent known feeding habitat under shifting ocean and climate conditions. Determining the composition of the right whales’ prey resource in a stable feeding habitat during a period of environmental change will inform con-servation efforts throughout their habitat range. We compared zooplankton sampled in the paths of skim-feeding right whales to the bay-wide zooplankton resource in CCB over 23 yr. The dominant zooplankton taxa in CCB were Pseudocalanus complex, Calanus finmarchicus, and Centropages spp. during the winter/spring seasons. The succession of these 3 dominant taxa — Centropages spp. to Pseudocalanus complex (day of the year [DOY] mean ± SD: 34 ± 3) to C. finmarchicus (DOY 92 ± 3)— has provided right whales with a stable, multi-month food resource in a small portion of their greater North Atlantic habitat. We found that right whales targeted aggregations of non-dominant prey groups: Pseudocalanus complex and Centropages spp. aggregations when Centropages spp. dominated the bay-wide zooplankton community; Pseudocalanus complex patches and C. fin-marchicus patches when Pseudocalanus dominated; and primarily C. finmarchicus copepodite stage CIV and CV aggregations when CIII dominated bay-wide abundances. Over the time series, we found that Centropages spp. abundance increased and C. finmarchicus decreased only at the beginning of the season. CCB remains a critical foraging habitat for right whales due to the phe-nological cycle of their prey and limited inter-annual changes in prey abundance.