Size-selective predation by Antarctic humpback whales data

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Animals aggregate around resource hotspots, but what makes one resource more appealing than another is difficult to determine, particularly when the scales of data collection differ from those of animal behavior. These challenges can obscure heterogeneity in a prey field that explains predator aggregation and species distributions. We used suction-cup attached bio-logging tags and active acoustic prey mapping to investigate humpback whale foraging behavior and prey characteristics in two Antarctic Peninsula fjords. Though geographically proximate, Charlotte Bay contained ~5x more whales than Wilhelmina Bay, a site previously known for super aggregations of whales and krill, inspiring our hypothesis that whale abundance is linked to prey biomass. Interestingly, we find that patch size and krill length at the depth of foraging better predict foraging effort than biomass. Tagged whales spent > 80% of the night foraging, and whales in both bays demonstrated similar nighttime feeding rates (48.1 ± 4.0 vs 50.8 ± 16.4 lunges/hr). However, whales in Charlotte Bay foraged for 58% of their daylight hours, compared to 22% in Wilhelmina Bay, utilizing deep (280-450m) foraging dives in addition to surface feeding strategies like bubble-netting. Daytime krill biomass density peaked between 200-300m depth, but patch size and krill size both increased below 300m, coincident with observed foraging depths. Large, mature, lipid-rich krill have previously been observed at these depths, likely feeding on detritus while avoiding predators. Selective foraging on larger krill by humpback whales has not been previously determined, but suggests hierarchical decision making to target more desirable parts of high-quality foraging environments. This behavior may be partially attributable to prey availability in an ecosystem from which baleen whales were nearly extirpated. More research utilizing a suite of techniques, including the dB differencing approach described here, is necessary to better characterize the ubiquity of size-selective foraging by baleen whales.


Type of resource software, multimedia
Date created March 2020


Author Cade, David E
Author Kahane-Rapport, Shirel R
Author Wallis, Ben
Author Goldbogen, Jeremy A.
Author Friedlaender, Ari S.


Subject patchiness
Subject Antarctic krill
Subject dB differencing
Subject active acoustics
Subject bio-logging
Subject lunge-feeding
Subject rorqual whales
Subject whale scale
Genre Dataset

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Cade, David E and Kahane-Rapport, Shirel R and Wallis, Ben and Goldbogen, Jeremy A. and Friedlaender, Ari S.. (2020). Size-selective predation by Antarctic humpback whales data. Stanford Digital Repository. Available at:


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