Surface foraging behaviour of the North Atlantic right whale, Eubalaena glacialis, and associated zooplankton characteristics

Right whales in Cape Cod Bay, Massachusetts, were studied to determine the relationship between their surface feeding behaviour and the density and composition of their planktonic prey. The swimming path characteristics of whales feeding, socializing, and travelling were compared. Zooplankton samples collected in the feeding path were contrasted with those from areas where whales were not present. Surface prey patches where right whales fed were dominated by Calanus finmarchicus (21 samples), Pseudocalanus minutus (n = 13), Centropages sp. (n = 3), and larval barnacles (n = 2). The zooplankton density in the feeding path of the whales tested significantly higher (Mann–Whitney U-test, P < 0.001) than at stations where whales were not present (mean total densities were 6.54 × 10 3 (SE = 1.03 × 10 3 ) and 0.87 × 10 3 (SE = 0.19 × 10 3 ) organisms/m 3 , respectively). Feeding was rarely observed in locations where the total zooplankton density was less than 1000 organisms/m 3 . The rate of change of direction in the feeding path (mean 19.3°/10 m of path) was significantly higher (P < 0.001) than for paths of whales travelling (mean 5.3°/10 m of path), reflecting area-restricted foraging behaviour.