Dorsal fin a pirate’s black sail
Here, and gone; here, and gone; here, and gone
Following seas eternally
Why are we sampling?
We are monitoring population recovery in both the resident killer whale ecotype (the AB pod) and the transient ecotype (the AT1 population), both of which suffered a significant number of deaths following the Exxon Valdez oil spill in 1989. These two killer whale ecotypes are separated based largely on diet preference—resident killer whales primarily eat fish while transient killer whales prefer marine mammals—and, despite their names, both ecotypes still remain within the Prince William Sound and Kenai Fjords study area.
As an apex predator, killer whales play a key role in the ecosystem through predation on fish and marine mammals. They are also one of the wildlife species of interest for viewing in the region’s vibrant tour boat industry in the region, which means they are valued by the public and can be closely monitored.
Where are we sampling?
This project is part of ongoing killer whale research in Prince William Sound and the Kenai Fjords region, Alaska. The overall study area stretches from the Nuka Bay, outer Kenai Peninsula region to Cordova on the eastern edge of Prince William Sound.
How are we sampling?
Our field work consists of three major activities: 1) identification of individuals; 2) biopsy sample collection; and 3) satellite tagging and location tracking. We use digital cameras to photograph individual whales in major resident pods and AT1 transient groups, and offshore killer whales to make identifications. We also photograph humpback whales when possible in collaboration with the humpback whale predation project conducted by John Moran and Jan Straley in the Gulf Watch Alaska program.
We collect biopsy samples for chemical analysis and genetics using an air powered rifle and small floating biopsy darts that are easily retrieved (see photo).
We attach ARGOS Mark 10 satellite tags to the whales with specially designed darts allow us to track movements and chart dive profiles of individuals over periods ranging from weeks to months. We also collect samples of fish or mammal prey from kill sites.
What are we finding?
- The fish-eating AB pod is recovering after 22 years but has still not reached pre-spill numbers. The marine mammal-eating AT1 population is not recovering and may be headed toward extinction. This project has determined that killer whales are sensitive to perturbations such as oil spills, but has not yet determined the long term consequence (e.g., extinction) or the recovery period required for AB pod.
- We were able to photograph 21 members of the AB pod in 2015. After several years of stagnant population growth, two new calves had been produced. While the population trend is stable and positive, at 21 animals, the pod has still not recovered to the pre-spill total of 28 whales. In contrast, the AT1 population continues to linger at seven animals, and shows no signs of recovery to pre-spill numbers. The AT1 population, which specializes in glacier fjord foraging, appears to have retreated from feeding in open waters and rocky shoreline of fjords to focus on glacial sites.
- Our analysis of biopsy samples over the past twelve years indicates a long-term trend of declining stable isotope (C13 and N15) and contaminant (mainly PCB and DDT) levels in resident killer whales that suggest a diet shift. The typical contaminant reduction due to natural attrition is approximately 2%, while Alaska resident killer whale attrition has been 8-10%. The concurrent decline of both stable isotope and contaminant values suggest a decrease in Chinook salmon and increase in coho and chum salmon in Alaska resident killer whale diets, which may represent a reduction in Chinook availability.
- 2015 was exceptional for coho and Chinook salmon abundance in Prince William Sound. By fall, resident killer whales had noticeable fat deposits behind the blowhole and on the body behind the jaw. When nutritionally stressed, the reverse is often the case with a depression forming behind the blowhole (termed the “peanut head” condition), and a narrow appearance in the area behind the jaws. The fat deposits were so noticeable that we termed it a “doughnut head” condition.