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National Marine Mammal Laboratory (NMML)

Cetacean Assessment and Ecology Program

Killer Whale Surveys in Western Alaska

photo of killer whales
Figure 1.  Two mammal-eating "transient" killer whales photographed off the south side of Unimak Island, eastern Aleutian Islands, Alaska.
Photo by Robert Pitman (NOAA).

In June (and July) 2005, the Cetacean Assessment and Ecology Program (CAEP) conducted killer whale surveys aboard the chartered fishing vessel Alaskan Enterprise. This comprised part of the ongoing research by CAEP to determine the distribution, abundance, stock structure, and diet of killer whales off western Alaska. The three legs of the 2005 survey focused on: 1) killer whales in the eastern Aleutian Islands region, 2) killer whales in the central Aleutian Islands region, and 3) North Pacific right whales in the southeast Bering Sea.

The focus on right whales was a continuation of a satellite-tagging project initiated by CAEP during the 2004 Alaska Cetacean Ecosystem (ACE) survey. A second priority of the 2005 survey was to collect, when possible, data on humpback whales as a component of the international North Pacific-wide SPLASH (Structure of Populations, Levels of Abundance, and Status of Humpbacks) project.

The main objectives of the killer whale surveys in 2005 were to obtain identification photographs, biopsy samples, and acoustic recordings of killer whales in order to identify individuals, document their movements, and examine the stock structure and diet of killer whales in western Alaska, with a focus on mammal-eating "transients" (Fig. 1, above). A team of scientists conducted sighting surveys and took photographs of individual whales while acoustic researchers deployed sonobuoys (underwater listening devices) to record killer whale vocalizations. Skin and blubber samples were also collected using remote biopsy techniques.

During more than 2,500 miles of sighting effort from 31 May to 10 July, there were 36 encounters with killer whales, including 14 encounters with mammal-eating transient killer whales and 22 encounters with fish-eating "resident" killer whales. Photographs collected during these encounters will be examined to determine the total number of individual whales observed and will contribute to mark-recapture estimates of abundance and movements. Thirty-four tissue samples collected from 19 transient and 15 resident killer whales will be analyzed to determine stock identity, assess contaminant levels, and infer dietary preferences. Biopsy samples were also collected from potential killer whale prey species for a fatty-acid diet analysis and for genetics studies. Humpback whale photographs and biopsy samples (16) were collected for the SPLASH project.

Observed instances of predation/harassment by mammal-eating killer whales included a group of transients feeding on a gray whale carcass on the south side of Unimak Island, in the eastern Aleutian Islands; two groups of transients harassing a gray whale mother/calf pair near the shore on the north side of Unimak Island; and a group of transients attacking and killing a northern fur seal near the Pribilof Islands in the southeast Bering Sea.

Sightings of more than 900 marine mammals during the cruise included the following species and number of encounters: killer whales (36), Pacific white-sided dolphins (2), harbor porpoise (46), gray whales (29), Dallís porpoise (138), sperm whales (68), Bairdís beaked whales (3), minke whales (102), fin whales (54), humpback whales (93), sea otters (65), Steller sea lions (13), and northern fur seals (130).

By John Durban


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