Sea Lions at the Bonneville Dam: 
Myths vs. Facts

California sea lions and Steller sea lions have been observed eating salmon at the Bonneville Dam on the Columbia River. Charging that the sea lions are posing a significant threat to the salmon, the states of Washington, Oregon and Idaho received  permission from the Federal Government to kill up to 92 California sea lions annually through June 2016. As Steller sea lions are currently listed under the Endangered Species Act, they are not subjects of this lethal management request.  Government estimates of the percent of the spring salmon run observed eaten by both species of sea lions have declined each year from 2007’s estimate of 4.7 percent of the fish to barely 1 percent of the run in 2012. Yet the sea lions continue to be blamed for eating “too much” of their natural prey and some charge that they must be killed to save the fish. The facts tell a different story.

Myth:   Sea lions are a non-native predator whose consumption of salmon is driving the fish toward extinction.

Fact:  Lewis and Clark noted the presence of seals and marine mammals feeding on fish as far up the Columbia River as the current site of the Bonneville Dam.  About 30 percent of the different salmon stocks in the spring salmon run are currently listed under the Endangered Species Act. The main causes identified for their peril are habitat loss, hydroelectric dams that block passage, competition with hatchery-raised fish, and harvest of fish in the river and ocean.   In its most recent report to Congress, the National Marine Fisheries Service (NMFS) stated that these salmon populations were all stable or increasing.

Myth: The consumption of fish by sea lions is one of the largest sources of mortality to the fish and it is unsustainable.

Fact: At the same time that sea lions are eating between one and four percent of the spring salmon run, the government has permitted fisheries in the river to kill up to 17 percent of these same spawning fish, asserting in documents that this level of impact is “minor if at all measurable.”  The government also concluded that 7 to 16 percent of adult fish are killed by the dams they must navigate and has said that this level does not jeopardize salmon. Far fewer fish are killed by sea lions than by fishermen or dams.

Myth:  The number of sea lions at the Bonneville Dam keeps increasing every year.

Fact: The number varies each year.  The highest number of individual California sea lions seen at the Bonneville Dam varied from 90 in 2004 to 54 in 2011.  The total number of California sea lions at the dam is lower in the last few years, and it is not explained by the number being killed. The amount of time an individual sea lion spent at the dam has declined in the past few years from an average of 20 days in 2008 to 9 days in 2010. It’s not always the same individuals at the Dam. Government scientists estimate that, depending on the year, 35 to 65 percent of animals are previously unidentified.  Sea lions come and go. New animals simply replace those who leave or are removed.

Myth: The number of fish eaten by sea lions is underestimated because it only considers the fish they eat during the daylight while they are at Bonneville Dam.

Fact: The estimate of fish consumption by sea lions at the dam already includes the very limited predation that occurs at night.  Studies have also shown that the diet of sea lions further down river is not dependent on salmon which are the minority of their diet downriver. Tracking studies show that when they enter the river, they are not spending time chasing salmon in the lower river. Predation is not as underestimated as some have alleged.

Myth: Managers have addressed all the other impacts to salmon and predation by sea lions is about the only factor that has not been addressed.

Fact: While there are measures in place to try to reduce mortality of fish caused by the dam’s interference with their passage, and habitat restoration efforts are ongoing, other impacts are either not addressed or still allowed to have a greater impact than the natural predation by sea lions, including:

Harvest Impacts:  Each year, fishermen in the river are allowed to kill between 5.5 and 17 percent of these same threatened fish runs in the spring and they often exceed the quotas.  In-river fisheries in some years kill more than 8 times as many fish as sea lions eat and still more fish are caught while they are at sea.

Hatchery Fish: In 2009, an independent blue-ribbon science panel reported to Congress that it was concerned about the impacts wild fish faced from competition with hatchery raised fish. The panel recommended reforming hatchery management, yet the federal government admitted in a 2012 report that no changes have been made.

Non-Native Fish: The Columbia River was intentionally stocked with bass, walleye, and other non-native fish to benefit sport fishermen and the states limit what fishermen can catch in order to keep these non-native fish abundant. These fish eat up to 2 million young salmon each year and compete for habitat, yet no efforts have been made to stop  or reduce this impact.

Other Natural Predators: A colony of terns was moved to reduce the birds’ predation on the salmon but the move made way for cormorants to move in and they ate even more fish than the terns. In 2011, the relocated tern colony was wiped out by eagles and gulls who ate the eggs and chicks. Interfering with the complex interplay of predator-prey relationships proved unsuccessful in this instance.

It’s a Fact: Killing sea lions will not change the future for the salmon. Addressing recommendations of scientists to reform hatchery practices and harvest management can make a big difference. So can removing non-native fish and making improvements to the salmon’s spawning habitat and passage upstream. Killing sea lions simply distracts attention from the fact that the greatest challenges to salmon recovery are not being addressed.

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