Graduate Thesis Or Dissertation
 

The Effect of Group Size on Individual Roles and the Potential for Cooperation in Group Bubble-net Feeding Humpback Whales (Megaptera novaeangliae)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/d504rp01h

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  • Group foraging is observed in many species as a means to increase the ability of members of the group to find and exploit patchy prey. Group foraging can be exhibited in a number of different contexts based on the relationships between the participants, including by-product mutualism. One variant of by-product mutualism is cooperation, in which individuals achieve a greater energetic gain by feeding together than they would alone. In cooperation, individuals adopt a role in the group, and in the most complex interactions there may be multiple roles, resulting in a division of labor that occasionally includes role specialization. Humpback whales (Megaptera novaeangliae) are one of the few baleen whale species that have been observed feeding in groups, utilizing behaviors that are hypothesized to be cooperative. One of these behaviors is group bubble-net feeding, which has been observed in the Northeastern Pacific, Northwestern Atlantic, and Southern Oceans. This study utilized multi-sensor archival tag data from 26 humpback whales from the southern Gulf of Maine, 4 from Southeast Alaska, and 1 from the Western Antarctic Peninsula to analyze individual bubble-net feeding behaviors and compare these across populations. Linear mixed effects models were used to determine if dive behaviors varied with group sizes to test the hypothesis that group size influences individual behavior. The results indicate that individuals in the southern Gulf of Maine, for which sufficient data were available, were consistent in their bubble-net feeding behaviors across group sizes, which suggests that individuals utilize set roles in group feeding events. There was evidence for a division of labor and role specialization among whales utilizing certain bubble-net feeding tactics in the southern Gulf of Maine. The three populations performed different variations of bubble-net feeding that are likely based on the speed and schooling patterns of the prey. The results are consistent with the hypothesis that bubble-net feeding is an example of by-product mutualism in these populations, though was not enough data to suggest that group bubble-net feeding in Southeast Alaska was a form of by-product mutualism. The prevalence of herding dives in feeding groups suggest that each individual takes on a role to herd the prey to the surface, and provide evidence against a producer-scrounger relationship in the southern Gulf of Maine, and potentially in the Western Antarctic Peninsula.
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