The role of kinship, cultural transmission, and independent innovation in humpback whale (Megaptera novaeangliae) predation on hatchery-released salmon in Southeast Alaska
In recent years, salmon hatcheries in Southeast Alaska (SEAK) have reported humpback whales (Megaptera novaeangliae) feeding on juvenile salmon during and after their release in late spring and early summer. Given that the abundance of humpback whales in SEAK is increasing at a rate of about 5.1% a year, this predation is likely to become an increasing problem. To gain a better understanding of why some individual whales prey on hatchery-released salmon, I investigated the role of kinship in this feeding behavior. I hypothesized that salmon-feeders would be closely related (e.g., mother and offspring) if this specialized predation was influenced by maternal experience. I used behavioral observations, long-term sighting histories, and genetic samples of humpback whales observed near Hidden Falls Hatchery during and after their release of chum and coho salmon (Oncorhynchus keta and O. kisutch) in May 2014 to compare life-history characteristics and estimate relatedness between individuals who fed on salmon and those who did not. I found that of the 22 unique individuals encountered during the study, only four were confirmed to be feeding on hatchery-released salmon. Of these four, I considered two -- IDs 2227 and 2571 -- to be "hatchery-salmon specialists." These individuals were encountered repeatedly during the study feeding on hatchery-released salmon and shared an unusual pattern of feeding behavior. ID 2571 had no sighting history before 2014, but ID 2227 has been observed near Hidden Falls in multiple years since 2008, suggesting localized site fidelity. A kinship analysis based on DNA profiles indicated that IDs 2227 and 2571 are not closely related, suggesting either cultural inheritance of hatchery-salmon predation, or independent innovation. Long-term studies of humpback presence at multiple hatcheries could determine whether our results hold true over time and space. If hatchery-salmon predation continues to spread through cultural transmission, humpback whales could have a significant impact on hatchery production.
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