Arctic Science Journeys
Last of the AT-1 Orcas
STORY: More than 300 killer whales, or orcas, frequent the blue-green waters of Prince William Sound. But only about 140 have been seen so often they're called residents. These resident killer whales live in tight-knit social groups called pods, with names like "AB pod" and "AJ pod"--given to them by scientists. These orcas feed on the region's abundant salmon.
But it's another group of killer whales that's getting a lot of attention these days. Scientists call this group the AT-1 group, and unlike their fish-eating neighbors, these orcas eat only other marine mammals.
The whales are attracting attention because with each passing year, the AT-1 group is getting smaller. In 1984, when scientists first started tracking it, 22 killer whales made up the group. They all seemed healthy, but over the next ten years their numbers plummeted. Today, only 11 of the whales remain, and Craig Matkin wants to know why.
"We're looking at it. We're trying to figure out just what all the possible problems might be. Things have very much changed with this group since 1984. We don't see any reproduction in the group and we see animals disappearing, so we're not sure what the problem is."
Matkin is a marine biologist with the nonprofit North Gulf Oceanic Society. He spends most summers following the sound's orcas, keeping meticulous notes about what they eat, where they go, and the distinct sounds they make to communicate. He's chronicled their habits and knows each one by the unique marks on their dorsal fins. But even after years of watching them, he has only theories about what's causing their demise.
"I believe they were in decline before we even started this study. I think it's the type of thing where a decline has begun and it was accelerated by this decline in harbor seals and potentially by other effects of the oil spill."
This may be a problem, but it doesn't explain why the group's six remaining females have been unable to reproduce. Lance Barrett-Lennard is a wildlife ecologist at the University of British Columbia helping to unravel the mystery. He says his research has turned up evidence that the killer whales of AT-1 may be a genetically unique population.
"It looks as if there may be some distinct genetic characteristics that they have. We may be looking at what I have called the Last of the Mohicans kind of scenario. It may be a relict population that's quite distinct from other killer whales on the coast. Or in fact it could be a small pocket of a larger population that exists somewhere out there that we haven't found yet."
Lennard's finding, coupled with what scientists have been able to learn about orca behavior, may help explain the lack of newborn killer whales. Lennard says orcas in fish-eating pods don't breed with orcas that eat marine mammals. And while scientists had thought the AT-1s would breed with other mammal-eating orcas, it seems their genetic distinction has left them without a similar pod with which to breed.
"It may be simply be that there are no other groups left of this possibly relict population."
Complicating matters is the fact that AT-1 females are getting too old to reproduce. Like humans, killer whales go through menopause. Lennard says he's concerned about what that means for the pod's future.
"I think unless something happens soon, unless we start to have calves in the next few years, the AT-1s are likely doomed."
Matkin and Lennard say that losing the pod would be devastating to the sound's ecosystem and could hurt the overall genetic diversity of the species. For Arctic Science Journeys, this is Debra Damron.
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks.
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