Aspects Of The Foraging Ecology Of Humpback Whales Megaptera Novaeangliae In Frederick Sound And Stephens Passage Southeast Alaska

The North Pacific humpback whale (Megaptera novaeangliae) population has been increasing at an average annual rate of ~6% since the early 1990s. In northern Southeast Alaska alone, there are now more whales than estimated for the entire North Pacific several decades ago. An understanding of how this growing population is repopulating traditional foraging grounds will benefit from detailed investigations of their prey preferences and trends in whale abundance and distribution relative to those prey. This dissertation examines these issues from late May until early September 2008 in Frederick Sound and Stephens Passage, a Southeast Alaskan feeding area historically used by humpback whales. The foundation for the study is an analysis of the life histories and abundance patterns of euphausiids, the principal prey of humpbacks in the area, during late spring and summer. Four species, Thysanoessa raschii, T. longipes, T. spinifera, and Euphausia pacifica, were identified in plankton net samples collected at random locations throughout the study site (n = 49) and in locations where a strong scattering layer was observed on a 120 kHz echosounder (n = 48). Both sample types varied in euphausiid species composition. Abundance patterns of immature euphausiids coupled with observations of females carrying spermatophores indicated differences between species in spawning schedules. Thysanoessa spp. began spawning in early April with the spring phytoplankton bloom and continued until late June, whereas E. pacifica began spawning in early June and continued until late August. This protracted recruitment of immature euphausiids was geographically widespread throughout the summer in contrast to adults, which, although present all summer, were found primarily in slope and shallow (

Relative to other baleen whale populations, the humpback whales Megaptera novaeangliae inhabiting Southeast Alaska are noteworthy in that they form large, enduring groups when foraging on schools of Pacific herring Clupea harengus pallasi. These groups use a variety of unusual feeding tactics when attacking prey, including the production of loud feeding calls, the release of bubbles, and the waving of their large pectoral flippers. Past observations of these groups have been largely anecdotal so little is known about their social behavior or the function of their feeding tactics. In particular, it is unclear if these pods are based on cooperative interactions or if they represent groups of individuals who are competing for prey that occurs in dense aggregations. In addition, little is known about the underlying social structure of these pods and whether they are composed of kin. The objective of this study was to employ field and laboratory techniques to gain insight into the function of the unusual feeding tactics, and to describe the basic social structure of these pods. In order to test the prediction that bubbles, feeding calls, and flipper movements represent prey manipulation tactics, herring schools were brought into the laboratory and subjected to various simulated humpback whale feeding behaviors. I found that these simulated behaviors produced strong avoidance responses from the herring schools, suggesting that humpback whales use these tactics to manipulate the behavior of their prey. Seven years of field observations revealed that humpbacks with enduring social bonds (i.e., high coefficients of association) specialized on herring and represented a small proportion of the entire whale population. Calves born to these "core members" were never observed to return and feed with their mothers in subsequent years, suggesting that these groups are not composed of close kin. This was verified by analysis of haplotype variation in the mitochondrial genome and microsatellite variation in the nuclear genome. Individuals within these pods appear to invest in by-product benefits, with the enduring bonds between whales in Chatham Strait (cf. krill feeders in Frederick Sound) possibly representing combinations of individuals performing compatible tasks (Le., bubble blower, herder, vocalizer).

In 'Humpback Whales in Glacier Bay National Monument, Alaska,' the United States Marine Mammal Commission provides a comprehensive study on the migration patterns, behavior, and conservation status of the iconic humpback whales in this particular region. The book is written in a scientific and analytical style, with detailed observations and data analysis that contribute to our understanding of the marine ecosystem within Glacier Bay National Monument. The authors utilize a multidisciplinary approach, combining biology, ecology, and environmental science to paint a holistic picture of the humpback whale population in Alaska. This book is a valuable resource for researchers, conservationists, and anyone interested in marine mammal studies. It sheds light on the importance of preserving the delicate balance of marine life in this unique and biodiverse region. The authors, affiliated with the Marine Mammal Commission, bring a wealth of expertise and experience to the subject matter, making this book a relevant and authoritative source for marine conservation efforts. Readers will gain insight into the complex interactions between humpback whales and their environment, which will deepen their appreciation for these majestic creatures and the continued need for conservation initiatives.

Increases in the humpback whale (Megaptera novaeangliae) population have generated considerable interest in understanding the foraging habits of these large marine predators in the Gulf of Alaska. Globally, humpback whales are classified as generalist predators but are known to exhibit localized differences in diet. Intensified predation pressure is of particular concern to resource managers, who have observed whales feeding at juvenile hatchery salmon release sites in Southeast Alaska. We assessed the diets and behavioral tactics of humpback whales foraging near Hidden Falls Hatchery release sites (in Chatham Strait, 2016 to 2018) to better understand their predatory effects on juvenile hatchery-reared salmon. We used skin biopsies, prey sampling, and stable isotope analysis to estimate whales’ diet composition. Aerial footage and photographic sequences were used to assess the foraging tactics used on this prey source. We observed three individual whales repeatedly feeding on juvenile hatchery-reared salmon, and we were able to sample them multiple times over a period spanning shifts in diet. Overall, the diets of these whales were higher trophically than other humpback whales foraging in the area, even before feeding on juvenile hatchery salmon started. These hatchery-feeding whales may be generally more piscivorous than other whales, which focused on planktivorous prey. Our repeat sampling, in conjunction with scheduled introductions of a novel prey source, provided a semi-controlled feeding experiment that allowed for incorporation and turnover rate estimates from humpback whale tissue in a way that was not previously possible for large, free-ranging cetaceans. Finally, during the course of this study we discovered an undescribed feeding tactic employed by hatchery-associated whales. We observed the use of solo bubble-nets to initially corral prey, followed by calculated movements to establish a secondary boundary with the pectoral fins that further condensed prey and increased foraging efficiency. Our study provided the first empirical evidence for what we describe as “pectoral herding”. This work deepens our knowledge about humpback whale foraging ecology, how this innovative species is able to exploit newly available prey, and to what extent they feed on commercially valuable hatchery salmon.