Arctic Science Journeys
Radio Script
1998

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Popcorn of the Sea
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INTRO: Pollock, a predatory fish that travels in huge schools, have--as far as anyone can tell--always lived in Alaska's Bering Sea. But beginning in the late 1960s, favorable ocean conditions allowed pollock to multiply in great numbers. As pollock boomed, stocks of herring, capelin and other fish that were the favorite prey of Steller sea lions, became scarce. Not long after that, sea lion numbers also began to decline. Where once more than 120,000 sea lions roamed, so few are their number that today they are listed as an endangered species. Canadian scientists now say pollock may be at least partly to blame for the demise of sea lions. But not everyone agrees. Robert Hannon has more about pollock, pinnipeds and people in this week's Arctic Science Journeys.

STORY: Clem Tillion is a tough, outspoken fisherman who's spent most of his life on the icy waters of Alaska, chasing salmon, herring, and cod. So when pollock started multiplying in the North Pacific Ocean, he knew rough waters lay ahead for the Steller sea lion. Pollock, he claimed, were for Steller sea lions what popcorn is for people--filling, but not very nutritious.

TILLION: "What I've said is that if you want to starve an animal to death while keeping its stomach full, pollock is the great thing to fill it with."

Researchers at the University of British Columbia agree. Andrew Trites, a marine scientist at UBC, just finished a three-year study of pollock in the sea lion diet. He says sea lions will starve eating only pollock.

TRITES: "When they ate pollock, they lost over a pound a day. Our Stellers would have starved to death eating pollock if we didn't switch them and give them some other types of prey."

Trites' studies were done at the Vancouver Aquarium, where sea lions of all age groups were fed their traditional diet of herring over a two-week period. Juvenile sea lions--thought by scientists to be the group most at risk in the wild--ate 6 kilograms--or about 12 pounds--of herring a day. The sea lions gained a half pound each day eating herring. Scientists then switched their diet to pollock. And while they were allowed to eat as much as they wanted, sea lions began losing weight.

TRITES: "They have to burn more energy to digest pollock than they do if they digest herring. They get less energy from the pollock--they're fewer calories. Plus they have to burn more energy to get those calories. Double-whammy."

Trites says sea lions lost weight because pollock lack the energy-rich oils and fat found in herring and other traditional prey. The findings don't come as a surprise to scientist Rich Ferraro of the National Marine Fisheries Service. He says Trites' study points out that Steller sea lions need diversity in their diet to remain healthy. But he admits such diversity is hard to come by in an ocean dominated by pollock.

FERRARO: "If that's what's available out there, wouldn't it be better or more advantageous to be feeding on pollock, as a survival ration, if you will, until something better comes along? In which case one could consider pollock to be an important safety net if nothing else."

With Trites' results now making their way through the scientific and environmental community, debate likely will center on how to improve prey diversity for seal lions. Clem Tillion believes fishermen should catch more pollock, because with fewer pollock in the ocean, traditional prey species may have a chance to recover.

TILLION: "I recommended that when the first big school of pollock showed up in Shelikof Strait in the 1960s. I said for God's sake, these things are gonna wipe out your crab. They don't have much value. The school was 75 miles long, three miles wide and 150 feet deep. It was just a big vacuum cleaner.

Francine Bennis, with the Alaska Marine Conservation Council, isn't so sure. She says trying to manipulate an ecosystem as complex as the Bering Sea might bring unintended consequences.

BENNIS: "We might get something we hadn't planned on. We don't believe it's a case of where you push one button down, another pops up. There's just an ocean of knowledge that we don't firmly understand, and to think that we can manipulate it in a predictable way is a bit of a stretch right now."

There's also the unanswered question of the importance of pollock to sea lions during the harsh Bering Sea winter, when female pollock are heavy with energy-rich eggs, called roe. The National Marine Fisheries Service's Rich Ferraro says such fish may be especially critical to the sea lion diet. Not coincidentally, industrial-scale fishing fleets also are targeting roe-bearing pollock, and that worries Francine Bennis with the Alaska Marine Conservation Council.

BENNIS: "We're looking at what can be the limiting factor right now and it seems to be winter prey. If we're doing something that will adversely impact that in terms of Steller sea lions, then we ought to be taking a critical look at that and see how we can mitigate it."

The 1998 winter pollock fishery began in early January. More than three-dozen large factory ships will catch the season's quota of just over 500,000 tons of pollock and roe in just six weeks. To be sure, scientists will be watching to see what effect it has on the region's remaining sea lions.

OUTRO: For Arctic Science Journeys, this is Robert Hannon reporting from Fairbanks, Alaska.


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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