A Feeding Aggregation of Humpback Whales Megaptera Novaeangliae near Kodiak Island , Alaska : Historical and Current Abundance Estimation

A photo-identification, mark–recapture study was conducted on a feeding aggregation of humpback whales Megaptera novaeangliae in the waters of eastern Kodiak Island between June and September 2002. Historically, a portion of this population was targeted in a local commercial whale fishery. The fishery was conducted in eastern Kodiak Island out of Port Hobron, Alaska, between 1926 and 1937 and resulted in the removal of nearly 1,600 humpback whales. An estimated 157 (95% confidence interval: 114, 241) whales were in the study area in 2002 based on the Schnabel maximum likelihood estimator (MLE) for closed populations. The Schnabel MLE of abundance in 2002 and historic catch values were used to back-calculate the historical abundance trend in the study area between 1925 and 2002 using a delay-difference model with a density dependent recruitment function. Historical abundances were calculated both prior to commercial whaling in 1925 and immediately post-whaling in 1938. Estimated abundance within the study area just prior to commercial whaling was 343 (331, 376). Immediately following the cessation of whaling in 1938, estimated abundance within the study area was 27 (14, 61). Results from this study show the Port Hobron whale fishery likely had a significant impact on the local humpback whale population. Authors: briana H. Witteveen and Kate M. Wynne are with the University of Alaska Fairbanks School of Fisheries and Ocean Sciences, 118 Trident Way, Kodiak, AK 99615. E-mail: bwitteveen@sfos.uaf. edu. terrance J. Quinn II is with the University of Alaska Fairbanks School of Fisheries and Ocean Sciences, 11120 Glacier Highway, Juneau AK 99801. Acknowledgments: The authors are indebted to a number of individuals whose assistance was essential to this project. Janice M. Straley, Dr. Robert J. Foy, and Dr. Brendan P. Kelly offered insight and guidance. Chris Gabriele of Glacier Bay National Park, Sally Mizroch of the National Marine Mammal Laboratory, and John Calambokidis of Cascadia Research shared their experience and suggestions and Lisa Baraff assisted in data collection. This manuscript was improved by the comments and suggestions of two anonymous reviewers. All research was conducted under provisions of NMFS Scientific Research Permit 473-1433. Sponsorship: Financial support for this project was provided by the Rasmuson Fisheries Research Center and NOAA Grant number NA16FX1270 to University of Alaska Gulf Apex Predator-Prey Project. INTRODUCTION Photo identification has been used for many years as a mark–recapture tool to estimate humpback whale populations and track their movements (Baker et al. 1986, 1992; Perry et al. 1990; Calambokidis et al. 1993; von Ziegesar 2001). Photo-identification studies have resulted in moderate understanding of humpback whale stocks in the North Pacific and have shown that, though they may converge on winter breeding grounds, during feeding seasons humpback whales are isolated into regional aggregations with very little exchange between them. Known feeding aggregations in the North Pacific are found along the California, Oregon, and Washington coasts, southeastern Alaska, and Prince Williams Sound, Alaska (Calambokidis et al. 1993; Straley 1994). A group of feeding humpback whales Megaptera novaeangliae is found year-round in the Kodiak Archipelago in the western Gulf of Alaska, with a peak in sightings occurring between June and October (Figure 1; Waite et al. 1999; Denny Zwiefelhofer, Wildlife Biologist, U.S. Fish and Wildlife, Kodiak National Wildlife Refuge, personal communication). These whales are currently assigned to the Central North Pacific stock of humpback whales by the National Marine Fisheries Service (NMFS), though no directed research has been conducted on this population (Angliss et al. 2001). Previous research on humpback whales around Kodiak Island has occurred opportunistically during line transect surveys for killer whales Orcinus orca in the early 1990s (Waite et al. 1999). These surveys suggest that the Kodiak Island humpback whales may be a homogeneous feeding aggregation separate from the other known feeding aggregations in Alaskan waters, including southeastern Alaska and Prince William Sound. However, until directed research tests this hypothesis, our understanding of the stock structure of North Pacific humpback whales remains incomplete, making the need for directed research efforts in this region critical for effective management.