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Data for "Predator-informed looming stimulus experiments reveal how large filter feeding whales capture highly maneuverable forage fish"

Supplemental Videos, Code and Data for "Predator-informed looming stimulus experiments reveal how large filter feeding whales capture highly maneuverable forage fish"

Size-selective predation by Antarctic humpback whales data

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.

Whale sharks increase swimming effort while filter feeding, but appear to maintain high foraging efficiencies

Whale sharks (Rhincodon typus) – the largest extant fish species – reside in tropical environments, making them an exception to the general rule that animal size increases with latitude. How this largest fish thrives in tropical environments that promote high metabolism but support less robust zooplankton communities has not been sufficiently explained. We used open-source inertial measurement units (IMU) to log 397 hours of whale shark behavior in Yucatan, Mexico, at a site of both active feeding and intense wildlife tourism. Here we show that the strategies employed by whale sharks to compensate for the increased drag of an open mouth are similar to ram-feeders five orders of magnitude smaller and one order of magnitude larger. Presumed feeding constituted 20% of the total time budget of four sharks, with individual feeding bouts lasting up to 11 consecutive hrs. Compared to normal, sub-surface swimming, three sharks increased their stroke rate and amplitude while surface feeding, while one shark that fed at depth did not demonstrate a greatly increased energetic cost. Additionally, based on time-depth budgets, we estimate that aerial surveys of shark populations should consider including a correction factor of 3 to account for the proportion of daylight hours that sharks are not visible at the surface. With foraging bouts generally lasting several hours, interruptions to foraging during critical feeding periods may represent substantial energetic costs to these endangered species, and this study presents baseline data from which management decisions affecting tourist interactions with whale sharks may be made.

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