A small but genetically distinct population of transient killer whales in Prince William Sound, Alaska is swimming towards the edge of a precipice. In November of this year, researchers, tourboat operators, and members of the public met in Anchorage to discuss conservation strategies to keep the AT1 group of killer whales from extinction.
First recognized as a distinct group in 1984, the AT1’s differ from other “transient-type” marine mammal hunting killer whales in several ways. Many transient groups range over 2400 kilometres, appearing in different locations from year to year; in contrast, the AT1 group normally confine their travels to waters in and around Prince William Sound and the Kenai Fjords—a range of 320 kilometres. Furthermore, the AT1 group has never been seen in association with either resident killer whales or other transient killer whales, even when these groups were nearby. The apparent social isolation of the AT1 group is supported by the results of acoustic research by Eva Saulitis, who found that the AT1’s have a “dialect” (repertoire of calls) that is almost completely different from those of other groups of transient killer whales in the North Pacific. Given the role that vocalizations play in mediating cultural and social interactions among killer whales, it is not surprising that the AT1’s are also genetically distinct from other transient killer whales in the North Pacific. Research by Dr. Lance Barrett-Lennard of the Vancouver Aquarium Marine Science Centre shows that the AT1 whales have significant genetic differences from transient killer whales in both British Columbia and other parts of Alaska.
Unfortunately, the unique character of the AT1’s may lead to their downfall. When first recognized in 1984, the group was comprised of 22 whales, including three juveniles or calves. Since then, no new calves have been seen and the group has dwindled to only eight individuals (this number includes a male that has been missing since 2002 and may be dead). Their ultimate fate depends on the ability of the two remaining breeding-age females to mate with the two remaining males, as their social isolation from other transient whales makes it unlikely that they will seek mates outside the group.
How did the AT1’s end up in this predicament? Their initial group size of 22 individuals was unusually small for a group of killer whales. Acoustic and genetic evidence suggests the group has been distinct from other Alaskan transients for many generations and that it was once much larger, indicating that it was already in decline when first identified.
Causes for the group’s recent decline are easier to pinpoint. From 1984 to 1989, the group’s size remained stable at 22 individuals. Then in March of 1989, the Exxon Valdez oil tanker ran aground on Bligh Reef, spilling more than 11 million gallons of oil into Prince William Sound. Within two years of the spill, eleven members of the AT1 group were missing and presumed dead. There is little doubt that these deaths were related to the effects of the oil spill; three of the missing individuals were even seen swimming through oil near the Exxon Valdez shortly after the spill. Three more individuals went missing and were later confirmed dead between 1999 and 2004, leaving the group with its present total of eight whales. These more recent deaths may have resulted from long-term effects of the oil spill, the impacts of threats the group faces today, or natural mortality.
Besides the possibility of another oil spill, the AT1 group faces a number of different threats. Like other transient killer whales, their tissues contain high levels of toxic organochlorine contaminants, which may be interfering with their ability to reproduce. Populations of harbour seals, a major prey item for transient killer whales, in Prince William Sound have declined significantly since the 1980s. This may have led to a shift in the AT1 group’s range: sightings of the group in the Kenai Fjord area, where seal populations have stopped declining, have increased recently while sightings in Prince William Sound have decreased. If this does indicate a shift in the range of the AT1’s, it could have negative consequences as more tourboats operate in the Kenai Fjord area than in Prince William Sound. Craig Matkin of the North Gulf Oceanic Society reports that Kenai Fjord tourboat operators are making considerable efforts to view the group, having learned of the depleted status of the population. Since transient killer whales rely on their ability to hear their prey while hunting, extended viewing times by tourboats could significantly impact the AT1 group’s ability to hunt, causing their population to become even smaller.
The eventual fate of the AT1 group is uncertain. They have been listed as “depleted” by the National Marine Fisheries Service (NMFS) and a conservation plan outlining future conservation, monitoring, and research for the group is currently being developed. Proposed conservation actions include further research on the winter travels, hunting areas, and reproduction of the group, stricter viewing guidelines for tourboat operators and kayakers, and an education campaign to explain why people need to give the whales space to hunt. In the end, the survival of the AT1’s rests on their ability to successfully reproduce. Unless the two remaining reproductive-age females have calves in the next few years, the group will not survive beyond the life span of its current members.
Although the AT1 group may prove to be beyond our help, they can serve as an inspiration for us to ensure that other groups of killer whales do not end up in the same dire straits. The disastrous effect of the Exxon Valdez oil spill on the AT1 group as well as many other kinds of marine life is a warning of some of the ecological risks associated with oil extraction and transportation. This is particularly relevant to British Columbians in light of current discussions concerning offshore oil development in the province. The levels of toxic contaminants in the AT1 group remind us to be conscious of what goes down our drains and into the ocean. And concerns about the effects of intensive viewing on the AT1s’ ability to hunt suggest the important role whale watching guidelines play in making eco-tourism a positive experience for whales as well as people.
Final status review of the AT1 group of killer whales from the Prince William Sound and Kenai Fjords area. Available online from NOAA Fisheries here.
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