What's Killing The Killer Whales?

October 29, 2008

During annual photo inventories conducted by the Center for Whale Research, scientists discovered that seven orcas were missing, presumed dead. Orcas, listed as Endangered under the Endangered Species Act, had been steadily increasing in number over the past several years following a steep decline earlier this decade.

While some of the deaths are unsurprising (particularly an old female and calves), the group also lost two female at the height of reproduction. "When you see adult, reproductive-age females die, then you start to get a bit more concerned about what might be going on," said Brad Hanson, a federal marine mammalogist. So what's killing the whales?

Scientists think falling salmon stocks are to blame. Salmon make up about 80% of the orcas' diet. Although salmon stocks in Washington have been in trouble for some time, Puget Sound orcas are known to range as far south as Monterey Bay in California to feed. Now the salmon in California and Oregon are suffering, too, meaning the whales are traveling hundreds of miles for minimal rewards.

"We've noticed that the drop is coincident with the crashing of king salmon supplies," said Ken Balcomb III, executive director of the Center for Whale Research. "Coastwide, there's a [salmon] problem. They used to be able to swim from Alaska to California and find plenty of fish. Now, nowhere in that range are they finding enough," Balcomb said.

What exactly all this means for the whales is uncertain. Killer whales have been known to switch to feeding more heavily on sea otters to survive. Of course, otters have their own problems to deal with, and as they disappear, so, too, do the productive kelp forests which support a staggering amount of life (for a summary, see this page). Otter declines have also been fingered in changing Bald Eagle diets - so if killer whales feed more and more heavily on them, we can expect a huge ecosystem shift.

One of the missing females was found. She was emaciated. Biologists took a biopsy before she disappeared, and will be analyzing it over the next few months to determine what happened - did she starve due to a lack of food, or was there something else (disease, etc) that led her to stop eating?

Even if there is less food resources available to the orcas, it may not be starvation that is killing them. They may not be getting enough food, sure, but they might not be starving to death, either.

It's likely that, as mammals, orcas burn fat when their low on food. Their fat, however, could be storing toxins like methyl mercury, PCBs and other long-lived industrial chemicals that act as endocrine disrupters. It is possible that, by burning fat reserves, orcas are exposing themselves to higher levels of these compounds, which have been shown to cause reproductive problems, diseases and a myriad of health issues.

Hanson and other scientists are trying to assess the health of the orcas by collecting their waste and what's in the breath they exhale through their blowholes. "We're really trying to look at what sorts of stressors are these animals up against," Hanson said, "because right now the animals disappear and we really don't understand what's happening."

The orcas are counted each year on my birthday (July 1). We won't know how many are truly missing until next summer, and some may be born or die before the next count. But it's likely that these seven are dead, since orcas rarely stray from their family packs. With this loss, the population of orcas in that area is down to 83, with less than twenty reproductively active females.

With salmon stocks still declining, the future doesn't look good for the Puget Sound orcas. In the initial review of their endangered status, the federal government predicted the extinction of Puget Sound orcas within 100 years, and with the way things are going, that is exactly where the whales are headed.

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