HOMER -- Larry Cabana was one of the first to drop a small crab pot into Kachemak Bay last summer. He used to fish in the bay commercially for crab, but the Tanner crabs disappeared in the early 1990s and the fishery closed. It had been six years since you could even catch a crab to take home and eat.
So it was a pretty big deal when Cabana pulled up more than 30 keeper-sized Tanners last July. More than 10,000 followed, as hundreds of Homer and Southcentral Alaska residents took advantage of the reborn sport fishery.
"The crab are definitely coming back," Cabana said.
The question now asked by scientists, fishermen and potluck-dinner guests is: Why?
Is the change related to a decline of cod and pollock in Kachemak Bay, and an increase in Dungeness crabs and shrimp?
Is it just a consequence of fishing closures letting the crabs bounce back? Or is the crab revival linked to broader long-term cycles of water temperatures in the region, something oceanographers have come to describe as the Pacific Decadal Oscillation?
Whatever the reasons, the mix of species along the northern Gulf of Alaska is starting to look a bit more like the early 1970s, when local crab and shrimp fisheries were big, cod were rare, salmon runs were weaker and winters were clear and cold.
That was the last time the North Pacific was in a cold phase of the PDO, which is a cycle of temperatures and currents that seems to shift every 20 to 30 years. The warm phase starting in 1977 brought an ecosystem shift that was great for salmon production but not so good for shellfish.
TREND IS HOLDING
Now there are signs that the cold cycle may be coming back. The shift began tentatively around 1998, and has been more pronounced since 2005. Deep-water temperatures outside Resurrection Bay were colder in the 2006-7 winter than they had been since 1972, and so far the trend is holding, researchers say.
If the regime shift proves to be lasting, the colder water would likely be a dominant influence over fishing and weather patterns in Southcentral Alaska for years to come, scientists say -- counteracting the worldwide global warming trend, at least for this region.
"The PDO has apparently switched now," said University of Alaska Fairbanks oceanographer Tom Weingartner. "But we can't say it's going to stay until some years have passed."
Predicting the future lives of crabs and salmon, like predicting future cold snaps, is ridiculously complicated and still beyond the reach of the super-computers.
Eight scientists asked last week if they thought they were seeing a North Pacific regime shift -- fish biologists, meteorologists, oceanographers -- all said they found the latest trends intriguing. But each was quick to add a personal list of caveats and quibbles.
Their basic message: Check back with us in a decade or two and we'll have better data.
"Explaining why things go up and down is really our ultimate challenge, and it's very difficult," said Gordon Kruse, a fisheries professor at the University of Alaska Fairbanks. As to whether there's a change happening right now in the Pacific, he said, "we're definitely due."
One difficulty with detecting a PDO shift is that weather changes come and go, regardless of any decades-long trend.
Then there are the short-range annual shifts known as El Nino (warm) and La Nina (cool), which can temporarily push Pacific water temperatures and weather patterns in a new direction.
And, of course, there is the much-discussed global warming trend, to which a cool phase of the PDO would run counter. Picture the PDO as a 20-year trend snaking above and below the horizontal line of the "normal" temperature.
Then tilt that horizontal line up slightly, to account for the higher temperatures being measured worldwide.
2008 WAS A COLD YEAR
A local cooling trend -- 2008 was the coldest year in Anchorage in a decade -- is not likely to go unnoticed by those who oppose difficult measures to reduce greenhouse gases.
But global warming skeptics "will probably have to eat serious crow" when the PDO shifts into its next warm phase and local temperatures really start cooking, said Ed Berg, an ecologist with the Kenai National Wildlife Refuge who has studied the oscillation's local patterns.
There are, in other words, plenty of ways to misread a chart of temperature readings. But if it's true that the Pacific has "locked in a strong cool phase," as NASA reported in December, what will it mean locally?
For weather, think back to the early 1970s, Berg said. Summers would tend to be cooler and wetter in Southcentral Alaska, he said.
The strongest influence of a cool-phase of the PDO would be felt in winter, said John Papineau, a meteorologist with the National Weather Service.
No need to think back to the 1970s, he said -- think back to that cold spell in early January, when a high pressure system locked clear, cold skies over Alaska. We'd see more winter periods like that, he said.
And fish? Press reports from the Pacific Northwest last fall were exultant about the atmospheric shift under way since 2007, saying the upwelling currents associated with cooler waters promised much better ocean survival for local salmon runs. What the stories didn't say was that, in the past, such improved runs in Oregon and Washington have correlated with worse survival for salmon in Alaska.
"We've been in a really good period right now, and that's not going to last," said University of Alaska salmon expert Milo Adkison.
If finfish such as salmon, cod, halibut and pollock do less well in the cool-water phase, shelfish tend to thrive. Indeed, surveys are planned that could lead to revival of a non-commercial fishery for Dungeness crab in Kachemak Bay, something that disappeared in 1997.
And in Prince William Sound, shrimp are so abundant that the state Board of Fisheries is considering opening a commercial pot fishery for the first time since 1991.
SO WHY ALL THE CRABS?
But what about those Tanner crabs in Kachemak Bay? Linking a local comeback like that to changes in the North Pacific will be a lot easier in hindsight than it is now, when everything is in flux, the experts say.
For one thing, it can take seven years for a crab to reach keeper size. Cold water is most helpful to small larvae, said Kruse, so a temperature shift in the last few years couldn't explain last summer's population boom.
State officials have wondered whether the shorter-lived cold shift starting in 1998 helped revive the bay's crab, said Charlie Trowbridge, a Homer-based Fish and Game shellfish biologist.
Tim Barnett, an oceanographer with the Scripps Institute in California who has studied Homer patterns, said the crabs' return could simply be due to recovery after years of overfishing.
Cabana, the lifelong Homer resident and veteran fisherman, sees his own pattern of local changes.
He remembers fishing for king crab with a handline off the deepwater dock on the Homer Spit as a kid. The first time he ever saw a Pacific cod, in the early 1970s, he had to ask his father what it was.
Soon the cod were everywhere and the crab disappeared. Now the cod are disappearing -- he thinks it's because of commercial fishing in the bay -- and the crab are coming back.
But Cabana doesn't think colder water is the reason. He trolls for feeder king salmon all winter and watches the surface water temperatures wherever he goes. He said it's definitely getting warmer in Kachemak Bay.
Find Tom Kizzia online at adn.com/contact/tkizzia or call him at 1-907-235-4244.
By TOM KIZZIA
tkizzia@adn.com