Sea Lion Decline Linked to ‘Junk Food’ Fish

By Brandon Loomis, Anchorage Daily News, Alaska

Mar. 18–Three decades after a change in ocean climate began creeping into the North Pacific, a team of scientists asserts with unprecedented vigor in a new report that the change is the central culprit in the crash of Alaska’s western sea lion population.

Andrew Trites of the University of British Columbia joined 27 scientists ranging from oceanographers to anthropologists in publishing the hypothesis and its evidence in the January issue of Fisheries Oceanography. The ocean still teems with fish, he said, but it’s a different mix that now thrives.

“It’s still a healthy system; it’s just different,” he said.

As a leading proponent of the so-called “junk food” theory — that Steller sea lions in the Gulf of Alaska and the Aleutians are eating fish of lesser energy value than they once got — Trites said his argument is now more forceful because it includes more parts of the puzzle.

“Thirty scientists got together to compare notes about things they’ve been observing,” Trites said. “Many of the things that we’re seeing are interrelated, and it appears that there are changes in ocean climate affecting Steller sea lions.”

Though sea lion managers at the National Marine Fisheries Service agree the new information is an impressive compilation of science, they aren’t ready to drop pollock trawling restrictions on the nation’s largest fishery aimed at preserving the endangered marine mammals.

“Oceanographic changes can change the distribution of fish, as can man’s activities,” said Lowell Fritz, a fishery research biologist with the agency. “Lots of things affect sea lion energy.”

Trites’ premise is that as the North Pacific switched to a warmer environment in 1976-1977, pollock and Pacific cod thrived while herring and other oily fish dropped off. He contends that the higher oil and calorie content of the formerly abundant prey offered better nutrition, so females more quickly weaned their pups and bred again.

In the warmer environment, the sea lions crashed by 80 percent by 2000, to about 62,000 animals. For unknown reasons, the much smaller eastern population in Southeast Alaska and the Pacific Northwest has climbed at the same time.

The warming phenomenon is like a longer-term El Nino, and scientists have yet to determine its causes. Periodic ocean warming has been the rule, Trites said, and archaeological evidence presented in the new paper suggests that it has devastated sea lions and the people who relied on them before.

Idaho State University anthropologist Herbert Maschner has studied human habitation patterns in Western Alaska, and found that people thinned out along with the sea lions when the ocean warmed 800 years ago. Likewise, recorded history demonstrates that sea lions were scarce the last time oceanographers say the North Pacific warmed, around 1870, said Maschner, one of the new paper’s authors.

During the latter warm-up, he said, Americans and Russians reported that Aleuts who relied on six sea lion skins for every kayak they built had to import the skins from California. And during the earlier warming, Maschner said, his archaeological inspections of old village sites shows that coastal Alaska’s human population crashed by 80 percent.

In Maschner’s view, the evidence unequivocally trounces the theory that overfishing or targeted fishing around critical sea lion habitat is the culprit.

“It’s all part of the big picture that says local fishermen have nothing to do with the sea lion crash,” he said.

For Fritz and the federal agency tasked with sea lion recovery, though, it’s not that simple. He said it’s clear that a warming in the North Pacific could affect prey species and sea lions, but his agency can’t control that.

“We have to play the hand we’re dealt in terms of the environment,” Fritz said.

The federal sea lion recovery plan lists pollock trawling and other fisheries as one of three potentially high threats to sea lion recovery. The others are killer whales and environmental variability such as ocean climate change.

Fritz said that after the government imposed fishing restrictions that protected critical habitat and gave buffers to sea lion rookeries, the population appeared to stabilize. At the same time, protections placed on sea lions in Southeast Alaska and California in the 1970s helped their numbers increase.

“We stopped shooting them and they did fine,” Fritz said.

In fact, the eastern population’s increasing health seems to contradict the notion that a warming ocean is bad for sea lions, he said. “Why is the sea lion population in Southeast increasing at 3 percent a year? It (climate change) can’t be so bad,” he said.

He added that herring populations actually seem to have increased from the 1970s to the 1980s. The sea lion problem, he said, “is a little more complex than is described in this paper. It’s not as cut and dried.”

Trites responds that sea lions in Southeast Alaska and points south appear to have a more varied diet, whereas the western stocks are living on cod and pollock. He says change in diet affects everything from breeding frequency to the relative effect of killer whale predation. Female sea lions who could give birth every year instead keep nursing pups for up to three years because of decreases in energy, he said, and killer whales naturally have a more pronounced limiting effect when the population already is down.

Trites sums up the theory this way: “If I put you out in a field of celery, there’s lots of food around, but you’re not going to be able to eat enough of it to extract enough energy.”

Samples from sea lion stomachs in the 1950s showed little pollock on the menu, Trites said. That’s a fact that Fritz acknowledges but said is insignificant because the sample sizes are so small.

The question now is whether global climate change may exacerbate the North Pacific’s natural cycles. Under normal circumstances, Trites said, the North Pacific’s warm period would end, and sea lions would rebound. Manmade climate change may introduce a new variable.

“While we’re trying to figure out what the rules of the game are, we’ve got global warming happening, which is probably rewriting the rules,” he said.

Daily News reporter Brandon Loomis can be reached in the newspaper’s Soldotna bureau at bloomis@adn.com or 907-260-5215, ext. 24.

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Copyright (c) 2007, Anchorage Daily News, Alaska

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