Predators

Many researchers see increased pedation by creatures such as sea lions, triggered by human-related changes in the ecosystem, as one of numerous factors contributing to the decline of salmon.

By Theresa Novak Salmon once were so abundant, they were a main food source for animals of the land, air and water. But as the number of salmon have decreased, concerns have increased that not enough is being done to control the number of natural predators that feed on them. Seals and sea lions are two examples of salmon predators that now seem out of balance with their prey. The population of these fur-bearing, ocean-going mammals dropped very low in the early part of the century due to demand for their pelts. Fishermen sometimes shot them on sight because they competed for fish and raided fishing nets. While seal and sea lion numbers rebounded after the Marine Mammals Protection Act in 1978 prohibited harming them, the numbers of salmon have fallen to historic lows. Some people thought the two trends were related, a view that gained popular attention by the well-publicized salmon-gobbling antics of Hershel, the determined sea lion.

In the 1980s, the big sea lion had a big appetite for mature steelhead salmon. His habit of gobbling them as they swam into the locks in the Ballard district of Seattle earned him the reputation for almost single-handedly wiping out a steelhead run.

Hershel also proved to be determined. Despite being moved many miles from the locks at Seattle, he found his way back.

Nowadays, Hershel is an attraction at Sea World.

But nuisance animals such as Hershel, who go into a feeding frenzy over migrating salmon, prompted an amendment to the Marine Mammals Protection Act allowing federal marine fisheries officials to remove--even kill--particular individuals that are devastating a salmon run.

"When you have 600-700 adult sea lions (in a given area) and you only have an expected return of 2,500 wild coho, you have to ask yourself whether that is an acceptable loss," said Robin Brown, a marine mammals specialist with the Oregon Department of Fish and Wildlife.

And as wildlife officials struggle to control one predator whose numbers are on the rise, the impacts of other predators are being better understood.

A three-year research project by wildlife biologist Daniel Roby of Oregon State University and OSU researchers Larry Davies and Carl Schreck indicates that sea birds known as Caspian terns are gobbling millions of salmon smolts as they swim down the Columbia River estuary and head toward the Pacific.

The terns have established what may be the largest breeding colony in the world. More than 8,000 nesting pairs live on a man-made sandbar called Rice Island, produced during dredging of the Columbia River. The seven-mile finger of sand has formed the perfect place for the terns, but its effect on salmon appears devastating.

According to research by the Roby-Schreck team, between 5 million and 20 million salmon smolts headed for the estuary in 1997 fell victim to terns nesting on Rice Island. That amounted to up to 30 percent of the smolts that were headed for the estuary.

The numbers vary so greatly because it isn't known how much of the loss of the smolts was due to terns and how much of it was due to gulls and cormorants, which also feed on smolts.

Yet as sea birds, the terns are federally protected, once again posing the question: How do you prevent one protected species from pushing another closer to extinction?

However, neither Brown nor the history of salmon predator control supports a full-scale attack on salmon predators such as the terns, mostly because such efforts in the past have produced unwanted side effects.

For example, after a 1991 study showed that northern pike, once known as squawfish, were eating up to 61 percent of the salmon smolts entering the pool of the John Day Dam, an aggressive program was started to reduce the number of these native fish.

The plan had some unexpected consequences. Predators that normally ate the northern pikeminnow began eating salmon instead. The same thing happened after populations of northern lampreys, once an abundant eel-like fish that was the preferred food of seals and sea lions, began declining because of changes in the lamprey habitat.

Non-native predators such as walleye, shad and small-mouthed and large-mouthed bass also prey upon salmon smolts. Largely unknown is what sorts of ocean-going predators may be seeking out salmon as food because their usual supply of prey is not available.

Those concerned with salmon restoration are taking action and gathering more information and authority so that natural predators don't wipe out salmon while humans continue efforts to restore salmon habitat.

Now the Oregon Department of Fish and Wildlife is seeking authority to remove or occasionally destroy nuisance seals and sea lions without having to go through federal channels.

The ODFW also is seeking ways to reduce the number of exotic fish that out-compete or eat salmon.

The way that salmon are released from hatcheries and barged around dams also is being changed to make it tougher for predators to catch the salmon when they are most vulnerable.

More will need to be done in the way of research and compromise so that the struggle for survival between salmon and their predators will again be a fair fight.

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