Berners draws feeding frenzy in spring

Bay attracts sea lions, whales and one of world's largest eagle gatherings

Posted: Sunday, May 01, 2005

The first warm rays of spring have a magical effect on Berners Bay.

As the surface of the estuary heats under the light of the sun, tiny plants begin blooming in the water.

In a matter of days, the bay's spring algal bloom segues into the rowdiest feast by wild predators in the Juneau region.

"For a while, it's the biggest restaurant in town," said Mike Sigler, a biologist at the National Marine Fisheries Service's Auke Bay Laboratory in Juneau.

It's also one of the best places to watch wildlife, amid a fjord-lined landscape dominated by the massive, snowcapped Lions Head Mountain.

With its diversity of marine animals and dense populations of bears, moose, wolverines and goats in its river valleys, "there just aren't very many places like it," said Neil Barten, Juneau area management biologist for the Alaska Department of Fish and Game.

While Steller sea lions, seals, whales and birds have plenty of other places to feed during the year in the Inside Passage, their density in Berners Bay during its annual hooligan run in late April and early May can be staggering.

The net weight of hooligan in Berners Bay has been known to range from 30 to 139 tons - a third of a million to 3 million fish.

In the late 1990s, biologists counted an average daily peak of 40,000 gulls and more than 600 bald eagles, all lining up on the tidal flats and shallow river beds for their chance to feast on the oily smelt.

The bald eagle gathering at Berners Bay is likely the third- or fourth-largest in the world, says Mary Willson, a Juneau biologist affiliated with the University of Alaska.

In studying Berners Bay, Willson and several other Juneau scientists have also gathered clues about the feeding patterns of Steller sea lions, which are declining farther west in Alaska.

For example, here in the bay, the scientists have documented a previously unknown cooperative feeding technique by sea lions.

Sometimes, the sea lions gather into large groups to feed on schools of spawning hooligan.

They dive deep and push the hooligan into one area of the bay, such as Slate Creek Cove. Then, they turn around and push the school in the other direction, Willson said.

The sea lions probably plow through the hooligan like combines through a wheat field, said Sigler, who tracks the hooligan from a boat using a powerful hydroacoustic signal.

Because the hooligan tend to school about 130 to 500 feet below the surface, no one has seen what the feeding looks like underwater, Sigler said.

"Sea lions could be flying through the fish and knocking them with their flippers," he said.

The hooligan feeding ritual that occurs in Berners Bay has not been closely studied in other areas of Southeast Alaska.

And scientists don't know very much about the whale feeding that occurs in Berners Bay during the period of the hooligan run, either. Whales are known to focus on herring, sandlance and capelin - which also spawn in the bay - but not on hooligan, according to the National Marine Fisheries Service.

So far, Berners Bay is one of only four locations in Southeast Alaska where scientists have seen groups of more than 200 Steller sea lions feeding voraciously on spawning hooligan.

Hooligan spawn in about 30 locations in Southeast Alaska, and Berners Bay is one of only 18 of these runs that have been surveyed for Steller sea lion feeding.

There are still many mysteries about sea lions' diet. Juneau scientists are curious about how much sea lions rely on seasonal feasting on prey such as hooligan.

They hope such answers could shed light on why Alaska's western population of Steller sea lions - which have a less diverse diet than the eastern population - are declining.

One answer may be that hooligan in Berners Bay - while not providing all the necessary nutrients in a sea lion's diet - is the right meal at the right time. Male and female sea lions need to fatten up before their long stay on the outer coast's rookeries, said Jamie Womble, a marine mammal biologist with the Auke Bay Lab.

Hooligan, the oiliest smelt besides the northern lampfish, provide a lot of energy for the sea lions, she said.

An estimated 10 percent of the sea lions in Southeast Alaska haul out in Lynn Canal during the run, Sigler said.

Lynn Canal sea lions also feed on hooligan runs on the Chilkat and Chilkoot rivers near Haines. Other large groups visit the hooligan runs in the Taku River and Taiya Inlet.

Scientists plan to study the Taku River hooligan run next year, Sigler said.

Unlike sea lions that can be spotted from the air, the movements of hooligan are much more difficult to track. They lack swim bladders, making it nearly impossible for ordinary depth sounders to find them, Sigler said.

Hooligan are poor swimmers and take advantage of tidal currents to get to their spawning areas on the Berners, Lace and Antler rivers.

On their way, "they are running a formidable gantlet of predators," said Willson, a retired federal biologist.

Sometimes, the bay's annual herring spawn, a notoriously unpredictable event usually occurring on the eastern shore of the bay, coincides with the hooligan run.

"Then, Berners Bay is a very lively place," Willson said with a hearty chuckle.

In April and May, hooligan and other smelt probably find shelter from predators in the murky water and the glacial silt streaming from the head of the bay.

Assailed by sea lions on their way to the river spawning grounds, the hooligan swim north through a submarine gully, called the Berners Trench, toward the head of the bay.

No one knows their cue, but suddenly they begin swimming up the rivers.

Some sea lions chase the spawning hooligan upriver quite a distance, Willson says.

"Everyone is just gorging on hooligan," said Willson, who has even seen mallards gulp down the silvery fish and songbirds snacking on hooligan eggs.

Windrows of little dead fish form on the beaches - easy pickings for shore birds, ravens and crows.

Crows bury their hooligan treats in the sand, marking them with a tuft of grass, Willson said. Judging from the rain of little dried-out fish, biologists believe juvenile ravens are hoarding their hooligan booty up in the trees.

"The eagles, of course, are very happy," Willson said.

A single female hooligan can lay 8,000 to 67,000 eggs, with an average of about 26,000. Incubation occurs over a period of 48 days, said Andrew Eller, a graduate student with the University of Alaska Fairbanks who is studying the early life of hooligan.

"The larva has hours to days before they hit the salt water. They must drift into food and begin feeding as soon as their yolk sac is absorbed," he added.

About a month later, the lens of fresh water washing out of the rivers also provides refuge for larval fish from huge masses of jellyfish lurking in saltier water.

Smelt larvae drift out into the bay, where they spend an unknown period before they are ready to go out to sea.

Around the same time, late May or early June, thousands of coho salmon smolt begin their migration out of the Berners River into the bay.

The Berners River has exactly the right kind of low-gradient, pond-filled habitat to support coho fry, said Leon Shaul, a fisheries biologist for the Alaska Department of Fish and Game.

"It's superb wetlands," he said. "After a heavy rain, it virtually becomes a lake."

The Berners River coho provide an average of 10,430 fish - about 16 percent - of the Lynn Canal drift gillnet fishery's total coho catch, which averages 64,800 fish.

A lull, of sorts, in biological activity occurs in June and July, with the exception of some early sockeye and chum salmon runs.

But it picks up again with pink and coho spawns in the bay's four rivers, beginning in late summer and continuing through October.

Throughout the year, however, the bay is filled with thousands of tons of juvenile and larval fish.

A 2004 survey by federal biologists at Cascade Point - a proposed ferry terminal site for the Kensington Mine on the east side of the bay - netted 16 species of anadromous and marine fish.

On the opposite side of the bay, the mouth of Slate Creek Cove - targeted for the mine's second ferry terminal - also appears to be a nursery for larval fish from June through at least December, according to the National Marine Fisheries Service.

It isn't just local fish that exploit the bay.

The eastern shore of Lynn Canal is a migratory route for all five salmon species traveling out of the Chilkat River.

Those fish spend their winters in Berners Bay before heading out to sea, according to the National Marine Fisheries Service.

"Availability of high-quality, undisturbed habitat and food resources are critical to survival during the early life stages of fish," stated National Marine Fisheries Service biologists in their March 18 biological opinion on the Kensington gold mine.

The biologists concluded that the mine wouldn't damage entire populations of species listed under the Endangered Species Act.

Still, they stated, the marine food web in Berners Bay is regionally important, supporting "a variety of ecological functions for the natural communities of Lynn Canal and northern Southeast Alaska."

On a recent Saturday morning, up to five groups of sea lions, totaling about 125 animals, had formed noisy rafts in the bay, belching out load groans and waving their front flippers in the sun.

One group was feeding on fish in Slate Creek Cove, porpoising and then diving out of view for minutes at a time.

While sea lions floated below, an avalanche roared down a steep chute on the eastern side of the bay.

A boatload of visitors blinked in surprise, then abandoned their watch on a raft of sea lions.

They steered over to photograph the slide - just one last spectacle the bay offered to its guests that day.



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