Aerial Surveys of Sea Otters in Yakutat Bay, Alaska 2005 Verena A. Gill and Douglas M. Burn February 2007 Technical Report MMM 2007-01 MARINE MAMMALS MANAGEMENT Fish and Wildlife Service Region 7, Alaska U.S. Department of the Interior AERIAL SURVEYS OF SEA OTTERS (Enhydra lutris) IN YAKUTAT BAY, ALASKA, 2005 BY VERENA A. GILL AND DOUGLAS M. BURN U.S. Fish and Wildlife Service Marine Mammals Management 1011 E. Tudor Road, MS 341 Anchorage, Alaska 99503 [email protected] USFWS Technical Report MMM 2007-01 February 2007 Table of Contents List of Tables...................................................................................................................................ii List of Figures ................................................................................................................................iii ABSTRACT ....................................................................................................................................1 INTRODUCTION...........................................................................................................................2 METHODS......................................................................................................................................3 Study Area...........................................................................................................................3 Survey Methods...................................................................................................................3 Data Analysis ......................................................................................................................4 RESULTS........................................................................................................................................5 DISCUSSION .................................................................................................................................6 Recommendations ...............................................................................................................7 ACKNOWLEDGMENTS...............................................................................................................8 LITERATURE CITED....................................................................................................................8 List of Tables Table 1. Results for a complete aerial survey of sea otters in Yakutat and Disenchantment Bays, and Russell and Nunatak Fjords, April 2005…………………………………………10 Table 2. Results for the replicate aerial surveys of sea otters in Yakutat Bay, April 2005………………………………………………………………………………………….11 ii List of Figures Figure 1. Study area of the April 2005 sea otter aerial survey in the Yakutat Bay area. ..............12 Figure 2. Survey transects and sea otter sightings for the complete aerial survey of Yakutat and Disenchantment Bays, and Russell and Nunatak Fjords, conducted 16, 17, and 20 April 2005..........................................................................................................................13 Figure 3. Replicate area for the April 2005 sea otter aerial surveys in Yakutat Bay. ...................14 Figure 4. Survey transects and sea otter sightings for the first replicate of the aerial survey of Yakutat Bay conducted 17 and 20 April 2005 ..................................................................15 Figure 5. Survey transects and sea otter sightings for the second replicate of the aerial survey of Yakutat Bay conducted 22 April 2005..........................................................................16 Figure 6. Survey transects and sea otter sightings for the third replicate of the aerial survey of Yakutat Bay conducted 23 April 2005 .............................................................................17 Figure 7. Survey transects and sea otter sightings for the fourth replicate of the aerial survey of Yakutat Bay conducted 24 April 2005 .........................................................................18 iii ABSTRACT Extensive commercial harvests of sea otters occurred from the mid-1700s through the 1800s which drastically reduced the population and eliminated them from much of their range. Sea otters were subsequently protected by the International Fur Seal Treaty in 1911. Sea otters were believed to have been extirpated by the early 1900s in Yakutat Bay, located near the northern extent of the southeast Alaska stock. In an effort to recolonize the population, sea otters were translocated to Yakutat Bay in 1966. Current sea otter distribution and abundance data from Yakutat Bay are needed to address potential management concerns regarding oil and gas development, subsistence hunting, and fisheries conflicts within the region. We conducted replicate aerial surveys of sea otters using established methods in April 2005 within the Yakutat Bay area. Our estimate of the overall sea otter population of Yakutat and Disenchantment Bays, and Russell and Nunatak Fjords is 1,582 ± 528 animals. The sea otter population has both increased in abundance and expanded its range since the last complete aerial survey of the area in 1995 when an estimated 404 otters inhabited the entire Yakutat Bay area. The annual rate of increase in Yakutat between the 1995 and 2005 aerial surveys was 14.6% per year, could be a result of reproduction alone. Based on this growth rate, current harvest numbers, and historic levels the northern sea otter population in Yakutat Bay should continue to increase and expand its distribution. We recommend regular aerial surveys to monitor this population and that these surveys sample a greater proportion of the low density stratum to account for the mobility of otters between the east and west coasts of the bay. In addition, we advocate increasing the sampling intensity of replicate surveys to improve the precision of replicate estimates. We also suggest that an aircraft with a lift flap design, such as the Aviat Husky, not be used for this type of survey in the future due to safety concerns associated with intensive search units used in this survey method. 1 INTRODUCTION Prior to the mid-1700s, sea otters Enhydra lutris occurred in large numbers in coastal areas of Japan, Russia (Kamchatka), the United States (Alaska, Washington, Oregon, and California), Canada (British Columbia), and Mexico (Lensink 1962, Kenyon 1969). Extensive commercial harvests of sea otters occurred from the mid-1700s through the 1800s which drastically reduced the population (Bancroft 1959, Lensink 1962, Kenyon 1969) and eliminated them from much of their range (Kenyon 1969, Riedman and Estes 1990). Sea otters were subsequently protected by the International Fur Seal Treaty in 1911. In the absence of harvest pressure, the population expanded from 11 remnant groups to re-colonize much of the former sea otter range. Despite legal protection, no remnant colonies of sea otters existed in southeast Alaska. As part of efforts to re-establish sea otters in portions of their historical range, otters from Amchitka Island and Prince William Sound were translocated to other areas (Jameson et al. 1982). These translocation efforts met with varying degrees of success. From 1965 to 1969, more than 400 sea otters (89 percent from Amchitka Island in southwest Alaska, and 11 percent from Prince William Sound in southcentral Alaska) were translocated to multiple sites in southeast Alaska (Jameson et al. 1982). In the first 20 years following translocation, these populations grew in numbers and expanded their range (Pitcher 1989), and is now considered a unique population stock, ranging from Cape Yakataga to Dixon Entrance (Gorbics and Bodkin 2001). Sea otters in Yakutat Bay, located near the northern extent of the southeast Alaska stock, were believed to have been extirpated by the early 1900s. In 1966, 10 sea otters from Montague Island, Prince William Sound, were translocated to Yakutat Bay (Calkins and Schneider 1985; K. Schneider unpubl. data). Surveys conducted by the Alaska Department of Fish and Game (ADF&G) in 1970 recorded 15 sea otters within Yakutat Bay (Calkins and Schneider 1985). By 1985, biologists at ADF&G speculated approximately 50 sea otters inhabited Yakutat Bay (Calkins and Schneider 1985). The last survey flown in the area was in 1995-96 by the U.S. Fish and Wildlife Service (Doroff and Gorbics 1998). The 1995 survey estimated a population of 404 otters for Yakutat and Disenchantment Bays, and Russell and Nunatak Fjords. At the time of this survey, there appeared to be unoccupied habitat within Yakutat Bay, and additional population growth was expected. As sea otters continue to re-colonize the southeast population stock, resource management concerns have arisen, including: 1) effects of oil and gas development and transport along the Gulf of Alaska coastline; and 2) conflicts between commercial and Native subsistence shellfisheries and sea otters. In order to address these management concerns, current and complete population estimates for the southeast population stock of northern sea otters are needed. This report presents the results of a survey for sea otters that was conducted in Yakutat Bay during April 2005. The remainder of the southeast stock, exclusive of Yakutat Bay, were last surveyed in 2002 and 2003 by the U.S. Geological Survey (Bodkin and Esslinger 2006). 2 METHODS Study area The study area is located along the northeastern Gulf of Alaska and included the waters of Yakutat Bay (940 km2), Disenchantment Bay (north of Point Latouche; 45 km2), Russell Fjord (151 km2),