Gulf of Alaska's salmon become scarce as ocean currents shift

Past cool phase linked to last big crash

June 20, 2009 

A second straight year of weak king salmon returns around the rim of the Gulf of Alaska has state fisheries biologists wondering if they might be staring into the face of a bleak future.

Troubling discussions of PDO -- an acronym for something called the Pacific Decadal Oscillation -- have been spreading coast-wide as kings come back weak in river after river. Historically, there are indications that geographically widespread weakness like these are tied to a shift, or oscillation, in Pacific Ocean currents that causes cooler waters to pool in the Gulf of Alaska.

A cool phase in the Gulf from 1947 to 1976 corresponds neatly with the last big crash in king numbers in Cook Inlet. Most fisheries biologists agree that overfishing with commercial nets contributed to a nearly three-decade-long depression in king numbers there. But there is widespread agreement there was more to it than just heavy fishing.

Climate was identified as a significant player by fisheries scientist Steven Hare in 1996. He linked the shifts in Alaska salmon runs to shifts in ocean-water temperatures and coined the phrase Pacific Decadal Oscillation. Fisheries biologists have been talking about PDO ever since, but it took on a new significance last year after ocean temperatures dipped and Kodiak Island, Susitna Valley and Kenai Peninsula king runs all plummeted.

The return to the Deshka River, traditionally the most popular and productive king stream in the Susitna Valley, dropped from the range of 30,000 to 60,000 fish per year to less than 8,000 in 2008. The return to the Anchor River, the most popular stream for roadside anglers on the Kenai, was sliced in half, from 12,000 to less than 6,000. And the return to the Karluk River on Kodiak Island plummeted to less than 800 fish, a fraction of the 4,000 to 6,000 that had been coming back there for years.

The downward trends have only grown worse this year. The king fishing season should at this moment be in full swing across the region, but faltering returns have forced closures of major Kodiak, Kenai, Susitna, and Copper River waters. And where streams aren't closed, there are still worries.

The early run of kings to the Kenai River -- one of the best known king-salmon streams in the world -- is lagging badly. As of Wednesday, there were still less than 8,000 of the big fish past the sonar counter on the river. In a good year, there would be twice that many by the same date.

Meanwhile, catches of salmon in commercial fisheries off the mouth of the Copper River indicate an even weaker return to the big glacial system that drains the Wrangell and St. Elias mountains. By June 13, the Copper River District commercial gillnet fishery should have caught nearly 26,000 kings. There have been 7,668 landed, the lowest king salmon harvest through the middle of June since at least 1969.

A LOT OF UNKNOWNS

Given the spread of faltering runs from Kodiak Island all the way to the Stikine River in Southeast Alaska, fisheries biologist believe they know where things went wrong:

"In the ocean" more than a dozen said when interviewed this week.

The how and what of went wrong there, however, leaves them scratching their heads.

"It kind of has everyone wondering,'' said Tom Vania, Southcentral regional management biologist for the Division of Sport Fish in the Alaska Department of Fish and Game.

"I wish I had the great answer for you on that,'' added Craig Erickson, the division's regional research coordinator. "But there's a lot of unknowns. We're good about counting, but we don't get to track them" once young fish head for the ocean.

"It's a big black box out there," said Keith Pahlke, a researcher for the state agency in Southeast. "Things have been wacky."

Southeast salmon managers were expecting at least decent returns to the Stikine and Taku rivers this year, two huge waterways that slice through the U.S.-Canada border. Like their colleagues in Southcentral, however, they have not seen near the number of fish they expected.

"The runs are looking pretty poor,'' Pahlke said. "The managers are stressing out over this. We thought we knew what we were doing here. It's pretty perplexing."

What biologists statewide have been doing in the decades since the newly formed state took over fisheries management from the federal territorial government in the 1960s is ensuring that optimum numbers of salmon escape fishermen in order to spawn. That is the reason they call their spawning goals the "escapement.''

For a couple decades, they have done a generally good job of reaching escapement goals. There have been notable misses -- too few fish here, maybe too many there -- but by and large the spawning grounds have every year been populated with appropriate numbers of spawners.

The only problem is the number of spawners are only a part of the picture.

Once salmon spawn, the eggs need to survive to become new adults. This is a process fraught with death on a massive scale even in the best of times.

A pair of kings might spawn 15,000 eggs. Close 60 to percent are usually destined to die. The other 40 percent hatch into alevins and eventually emerge from the gravel as fry. Only 10 to 20 percent of those, if that many, are likely to survive a year or two in freshwater to grow into smolts headed to sea.

Thus, from those 15,000 eggs, there will come, at best, only 600 to 1,200 young fish finally ready to go to sea for one five to years. A lucky few of them are destined to grow fat roaming the ocean. Most will die and never come back.

If 5 percent survive, a run of only 200 pair of adults can produce a return of 3,000 to 6,000 adults -- a run the size of the Karluk.

But ocean survival is almost never this high, and it can drop so low the return per spawner might slide to one or two per adult. When that happens, the situation looks a lot like it does along much of the Alaska coast this year -- grim.

PHASES TEND TO LAST

Biologists know in general how young fish die in the ocean. Some starve. Some are eaten by other fish or birds or marine mammals. Sometimes the are killed by disease.

That water temperatures influence this equation is documented. Exactly how is not. Reductions in plankton productivity because of cooler temperatures could lead to changes in the food chain that cause young fish to starve. Poor food supplies could just leave young fish so weak they are more vulnerable to predation or disease. Or, changing weather could simply make the ocean environmental more hospitable to the predators that feast on the young fish.

Whatever drives numbers down, it is clear that when North Pacific temperatures dip, Alaska kings usually come back in smaller numbers for a long time. Based on more than 100 years of data, scientists calculate PDO phases generally last 20 to 30 years, although there has been some confusing flip-flopping in the past decade.

A 20-year warm phase ended in 1999. Three years of cold water followed. Scientists thought they were about to see a permanent shift, and then water temperatures began to shift back the other way. From 2003 through 2006, it was warm again.

Almost 60,000 kings swarmed the Deshka in 2004.

By 2006, another slide into a cool phase was under way. The results of that began became obvious in local waters last year. Whether this is permanent or temporary, of course, won't be known for years.

Alaskans, and salmon lovers all along the Pacific coast, can only watch and wonder, for what has traditionally been bad for the north has been good for the south. Water temperatures shifts that depress Alaska king salmon runs have, at least historically, boosted runs to the Pacific Northwest.

Cooling ocean temperatures that worry Alaska salmon biologists have made their colleagues in the Northwest hopeful. Because of the temperatures, they were looking for a good return of kings to the Columbia River this year, but aside from an unprecedented return of jacks -- immature salmon that come back before they are supposed to -- that hasn't really happened.

It's only one more question to the many about what goes on offshore in that big, black box called the ocean.

For all scientists know about the lives of salmon in the ocean, said Robert Walker, a scientist with the High Seas Salmon Research Program at the University of Washington in Seattle, there is still much they don't know.

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