Seals And Sea Lions Eating Salmon
April 20, 2011
It's not a rare scenario for salmon or steelhead anglers fishing in the bays and tidewater river reaches along the Pacific Northwest. Fish on, then a sudden hard tug on the line and their catch is gone — into the jaws of a marauding harbor seal or California sea lion. Commercial fisherman have their complaints as well, accusing these ubiquitous and resourceful marine mammals of taking large numbers of salmon and steelhead — that would otherwise be caught for human benefit — from their nets or the open ocean. In the minds of many West Coast sport and commercial fisherman, the way to better salmon and steelhead fishing, as well as protecting endangered and threatened stocks, is to reduce the population of seals and sea lions by lethal means. But is that really the case?
"That is a longstanding question," says Robin Brown, Marine Mammal Research Project Leader with the Oregon Department of Fish and Wildlife. "People in the Pacific Northwest who have been interested in salmon and steelhead for the past 150 years have looked at seals and sea lions and other predators as competition."
And well they should. In pursuit of their prey — primarily fish — seals and sea lions are clever, adaptable, and relentless. From the 1920s to the late 1960s, Oregon and Washington paid a bounty on seals and sea lions, and large numbers of the animals were killed. From the late 1940s to the early 1960s, Oregon even retained the services of a professional hunter who was charged with culling the Columbia River population.
Members of the taxonomic order Pinnipedia, seals and sea lions are commonly referred to as pinnipeds. California sea lions range along the West Coast from Baja California to British Columbia. Males may reach 1,000 pounds and seven feet long, while females run a foot shorter and about 400 pounds less. The West Coast population of California sea lions is about 200,000.
Most California sea lions off the coasts of Oregon, Washington, and British Columbia are males, up from their breeding grounds off southern California and Mexico. Arriving in the fall, they remain in the Pacific Northwest throughout the winter, departing south en masse in May. The females tend to spend the winter in Golden State waters with their pups.
Considerably smaller at 300 pounds, harbor seals are year-round residents to the entire West Coast. Shyer and more secretive in their feeding habits than California sea lions, the total population is about 330,000.
With more than a half-million fish-eating pinnipeds prowling the coastline, bays, and river mouths, you have to wonder if predation is having a serious impact on West Coast anadromous fish numbers throughout their range.
"The answer to that is that it's site specific," explains Joe Scordino, Deputy Regional Administrator for the Northwest Region of NOAA Fisheries. "It can be a problem at some sites, and in some places with exactly the same conditions it isn't a problem at all."
Although many anglers think pinnipeds are gobbling up salmon and steelhead left and right, in reality the sea-going carnivores don't play favorites at dinnertime.
"They eat every kind of fish imaginable or whatever is in season or locally abundant," says Brown. "They don't just target steelhead and salmon." For example, in the mid-1980s, Brown and colleagues examined the stomach contents of 100 seals that had drowned in commercial fishermen's nets. "Ninety seven percent of what we found in the stomachs were smelt, because they were so abundant," he says.
But, as NOAA Fisheries' Scordino points out, there can be problems in certain places, usually where circumstances offer easy pickings for an animal that is a fast learner when it comes to procuring a meal.
One of the most well-known examples of this was in the mid-1980s to early 1990s when a small group of California sea lions congregated by a fish ladder at Ballard Locks in Washington State, happily feasting on half of a run of wild steelhead. Some 50 sea lions make an annual spring pilgrimage 146 miles up the Columbia River to the base of Bonneville Dam to feed on the salmon that gang up at the fish ladders. Another 10 or so sea lions pull the same trick on spring Chinook salmon at Willamette Falls on Oregon's Willamette River. A group of pinnipeds has learned to scoop chum salmon off their spawning beds on a tributary of Washington State's Hood Canal.
Determining how many salmon and steelhead pinnipeds actually take is problematic. NOAA-sponsored research has documented up to 50 percent of fish in a run showing scars from brushes with seals or sea lions. "But those are the ones that got away," says NOAA's Scordino. "You don't know how many were eaten." But, qualifies Scordino, "Because you have 500 seals hauling out in an area doesn't mean that they are eating all the salmon."
Nevertheless, when groups of pinnipeds or an individual animal learns to target a particular run at a vulnerable location, that can be a problem — especially with 26 stocks of Pacific salmon and steelhead currently listed under the Endangered Species Act. "Some people will argue that we have too many animals and that we should cull half of them," says Brown. "We have no scientific evidence that culling seals and sea lions would give us more steelhead and salmon. But it would be reasonable to argue that if there is an animal at the mouth of a small spawning stream taking out all the fish, we might want to remove that animal."
While from a fishery manager's perspective that may be a reasonable proposition, the Marine Mammal Protection Act of 1972 makes that approach more than a little difficult. The Act provides strict protection for seals and sea lions and transferred management responsibility from the states to the federal government, leaving fishery managers with limited avenues for dealing with problem pinnipeds.
"There are very few options," says Brown. "They are tough, hard-headed animals that can put up with a lot, especially when their motivation is food. About the only thing that really stops these animals is something that hurts, or potentially kills them."
Although it is not easy, it is possible to get permission to take some management action. In the case of the Ballard Locks sea lions, the Washington Department of Fish and Wildlife was able to secure the go-ahead to remove the offending animals. Fortunately, a zoo agreed to take the sea lions, saving them from being euthanized, along with an almost certain public relations fiasco.
The question of how Atlantic salmon populations off the New England coast are impacted by seal predation is far murkier, since very little field research has been done on the subject. "Much of our information comes from adult salmon traps," says Orono, Maine-based NOAA Fisheries fish biologist Rory Saunders. "And, lo and behold, there are a lot of seal scars on adult Atlantic salmon."
What those impacts might actually be is no small question in the face of an expensive, decades-long effort to recover wild runs of Atlantic salmon in the Northeast. "When they declared Atlantic salmon endangered in five rivers in Maine, one of the things people pointed to were seals," says seal researcher James R. Gilbert of the University of Maine. "Our salmon migrate up near Greenland, and they go through a population of five million harp seals. They are exposed to a lot of predators."
Although there are no sea lions off the coast of Maine, there are four seal species present. These include harbor and gray seals, which are year-round residents, and harp and hooded seals that show up during the winter.
Unfortunately, trying to figure out how many fish they eat in the open ocean is an impossible task. Gilbert and colleagues did a literature search of studies that examined the stomach contents of seals in Maine and Northeast Canada, finding only five instances of seals with Atlantic salmon parts in their guts. It may be that the low numbers of Atlantic salmon render them a relatively minor part of a seal's diet.
Interestingly, the real threat that seals may pose to wild Atlantic salmon recovery, in Maine at least, may be an indirect one. Just as some West Coast pinnipeds learn how to corner salmon and steelhead at fish ladders, some Northeast seals have figured out how to raid salmon-farm net pens, occasionally causing the escape of farmed fish into local streams, carrying with them the dangers of interbreeding with wild fish, spreading disease and competition for food and space.
Ultimately, when predator populations threaten prey populations, the real issue is more likely to be not enough prey rather than too many predators. "Salmon have always encountered predators," says Saunders. "What is new is the lowered abundance of salmon and other anadromous species that predators would normally feed on."
A whole array of factors affects steelhead and salmon population levels, ranging from ocean conditions to habitat quality. Seals and sea lions rarely threaten healthy runs of fish. When abundance declines, people look around for something to blame, other than themselves. That finger often points to predators, followed by demands for their destruction. In the greater scheme of things, predator eradication programs seldom increase abundance of prey species except in very narrow circumstances. This is especially true in the case of salmon and steelhead, where population declines can be traced largely to human activities and development.
"The way we like to frame the conflict," explains the Oregon Department of Fish and Wildlife's Brown, "is that when fish populations are healthy and abundant, natural predators have the least effect on fish populations." From that perspective, the best way to protect salmon and steelhead from predators is to continue conservation efforts to make abundance their normal condition.
Jim Yuskavitch is the editor of The Osprey, a Federation of Fly Fishers newsletter dedicated to wild steelhead. He lives in Sisters, Oregon.