Eulachon run draws many predators

Posted: Friday, April 20, 2001

Hunkered at the edge of the river, we watch them pass thousands upon thousands of small, cigar-shaped forms, shadowy in the murky glacial water, moving slowly upstream in a long black column near the shore. It is spring, and the eulachon are running.

These are the lucky ones; they've made it past the terrible gauntlet near the mouth of the river, where hordes of milling sea gulls gulp them down and hundreds of sea lions and seals make a bloody harvest. We are camping here in Berners Bay to study the predators that come to feast on the annual bonanza of eulachon.

Eulachon, a kind of smelt, are about 8 inches long. Like salmon, they are anadromous fish, maturing in the ocean but returning to fresh water to spawn.

Spawning occurs in the lower reaches of the rivers, seldom more than a few miles upstream. After spawning, the adults drift slowly back to salt water. The prodigious effort of the upstream migration and spawning has depleted their stores of energy. Weak swimmers at best, they are very feeble now, and most of them die on their way back to the sea. Windrows of little carcasses line the shallows of the river or are stranded by the tides in the estuary.

These small fish range from northern California to south-central Alaska. They have over 20 common names, including oolichan in Oregon and hooligan in Alaska.

To the Tlingits on the coasts of Southeast Alaska, they are sk. Sometimes called candlefish, eulachon have a very high oil content - as much as 20% of the body weight. Tlingits used the oil as food, preservative and an important commodity of trade. Trade routes known as "grease trails" ran over the mountain passes from the coast to the interior and were the conduit by which eulachon oil reached inland peoples. Eulachon are still culturally important to many Tlingits.

The high oil content that made them so valuable to native peoples also makes eulachon a valuable prey for many wildlife species. In Berners Bay, the eulachon commonly run in late April and early May, although some runs in Southeast are earlier. They provide spring food for many animals emerging from the long winter, on migration to breeding grounds, and preparing to produce offspring.

When the eulachon are running, their predators congregate.

Many Steller sea lions and harbor seals gather at the mouths of the rivers as the run begins; some even follow the fish up-river. Gangs of 50-100 sea lions sometimes line up, shoulder to shoulder, cooperatively chasing fish across the bay. The run occurs just before they go to their breeding rookeries to give birth to their pups. By foraging on eulachon, male sea lions can store energy for their long fast on the rookeries and females can obtain energy for the costly process of milk production.

The number of gulls increases dramatically as soon as the eulachon arrive at the river mouths, increasing from a few hundred to tens of thousands in just three days. They forage mostly by cruising over the rivers, plunge-diving after their prey, and by stealing fish from each other. Between bouts of frenzied feeding, the gulls loaf on adjacent sandbars.

Other birds come as well, though in smaller numbers.

Migrating red-breasted mergansers gather in hundreds in the bay. A few dabbling ducks, such as mallards, pintail, and green-wing teal nibble on dead or moribund eulachon. Shorebirds and even songbirds peck bits of flesh from dead fish on the shore and pick loose eggs from the shallows. Northwestern crows glean from the shoals of dead eulachon and hide their booty in the meadow grasses. Nesting ravens feed eulachon to their chicks and store the extras in the trees nearby.

Then there are the eagles. The numbers of bald eagles build more slowly than those of the gulls, reaching a peak of perhaps a thousand as spawning ends and the weary adult eulachon drift downstream. A few eagles nest near the action, but most come from other places to feast at the cafeteria provided by the eulachon. They line the channels, perching on logs and stumps washed down by floodwaters and in the trees on the riverbanks. At low tide, sometimes a hundred eagles crowd onto a single sand bar, bickering over the goodies that drift by.

This aquatic richness does not last very long. The eulachon come into the rivers and spawn for perhaps a week or two; their seaward drift may take two weeks. Then it is over.

But these little fish have fueled the reproduction of harbor seals and Steller sea lions and fed thousands of northward-migrating Thayer's gulls on the way to their nesting ground in Arctic Canada. They temporarily support one of the largest concentrations of bald eagles in North America. Their bodies nourish thousands of immature gulls and eagles after a long winter when foraging was difficult.

In short, the eulachon have provided an important seasonal pulse of food resources for many wildlife predators and, still, enough survive that their offspring will come back, in turn.

Mary Willson did field research in Berners Bay during six spring seasons. She is a retired professor and ecological researcher: an adjunct professor in School of Fisheries and Ocean Sciences and the Institute of Arctic Biology, UAF. Juneau Audubon Society is sponsoring its sixth annual Berners Bay cruises on May 5. For further information call Judy at 789-9544.

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