Feeding tactics of resident Bryde's whales in New Zealand

Large predators typically feed on proportionally sized prey but the world's largest animals, baleen whales, bulk feed on plankton and small fishes. While most baleen whales migrate to feed on polar aggregations of nutritious zooplankton prey, Bryde's whales (Balaenoptera edeni brydei and B. e. edeni) inhabit less productive warm-temperate waters with variable prey abundance and quality. Off New Zealand, Bryde's whales target both fish and zooplankton, some with lower calorific value. We use multisensor tags (n = 4) and visual observations from drones and boats (n = 52) to reveal that Bryde's whales employ specialized feeding tactics matched to prey type. Zooplankton-feeding at the surface involved multiple head-slaps that presumably aggregate zooplankton followed by a side-lunge. Whales exploiting plankton patches swam in tight circles, performing up to 33 lunges (M = 5.5 +/- 6.1) per feeding bout. In contrast, whales targeting fish performed faster vertical lunges. With both prey types, whales concluded lunges with a similar to 90 degrees roll probably to minimize prey escape at the surface. The diet plasticity and dynamic behaviors of Bryde's whales are key to increasing their foraging efficiency. This may be essential for the whales to meet energetic demands year-round with a variety of prey in New Zealand waters.

Automated summary

This article examines the feeding tactics of Bryde's whales in the waters of New Zealand and finds that they employ different feeding behaviors according to the type of prey, thus increasing their foraging efficiency.