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From Nature magazine
What do you do when a charismatic marine mammal is wreaking havoc by gorging on a threatened species that humans also find delicious? That’s the awkward problem faced by wildlife managers along the Columbia River in Washington and Oregon states, where sea lions have been congregating for the past decade to feast on salmon waiting to climb the fish ladders at the base of the Bonneville Dam on their spring voyage upriver to spawn.
To protect the Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) in the river, some of which are listed as threatened populations, in 2008 the states of Washington and Oregon obtained permission from the National Oceanic and Atmospheric Administration in Silver Spring, Maryland, to kill California sea lions (which are normally protected) seen feeding repeatedly at the dam, after attempts to frighten the animals away proved ineffective.
In response, the Humane Society of the United States, based in Washington DC, and others filed a lawsuit to stop the practice and their legal challenges have continued. A US district court in Portland, Oregon, is expected to hear full arguments for a final ruling in the next few weeks. In the meantime, more than 40 California sea lions have been killed and 11 transferred to aquaria and zoos.
Survey data collected by the US Army Corps of Engineers during the years of the cull show that numbers of California sea lions (Zalophus californianus) are decreasing at the dam, along with the amount of salmon they eat. The corps and others attribute this to the removal programme.
Muscling in
But the cull may have been too successful. Last year, the larger Steller sea lions (Eumetopias jubatus), which arrived in earnest at the dam in 2005 and have returned in greater numbers each year, outnumbered California sea lions for the first time and ate fully half of the predated salmon.
“Part of this switch toward the Steller sea lion abundance may be due in part to success of the removal programme,” said Doug Hatch of the Columbia River Inter-Tribal Fish Commission in Portland, Oregon, speaking at a meeting of the American Fisheries Society in St Paul, Minnesota this week.
The problem with this shift is that Steller sea lions are themselves listed as a threatened species, meaning that 'hazing' — disturbing them with, for example, rubber bullets — is the only option for dealing with them. But the eastern stock of Steller sea lions, which includes those at Bonneville, is under review for delisting as threatened, so that protection may not last.
Counting the damage
A key issue is exactly how much the sea lions are affecting the salmon, particularly the species that are listed as threatened. This is a difficult question to answer. Accurate numbers are available from near the dam, where sea lions and the prey in their mouths can be counted directly, but the dam is 235 kilometres from the mouth of the Columbia River and sea lions are present patchily throughout this length.
Hatch’s best estimate is that sea lions take on average a little over 10% of the listed populations annually between the dam and the ocean. He and his colleagues are tagging sea lions to improve understanding of where the mammals go within the river and beyond.
The Humane Society says that the cull focuses on the wrong problem — sea lions — instead of reducing the allowable fishing catch, improving habitat, and reducing losses from hydropower, which it maintains are greater threats to the fish.
Archaeological records suggest that sea lions are recent arrivals in the Columbia River, but researchers are finding that the smorgasbord of oily fish is expanding more than their range. “We have captured and handled the largest California sea lions anyone has ever touched,” says Robin Brown, a marine mammal specialist at Oregon Fish and Wildlife in Corvallis. The biggest weighed 658 kilograms, compared to a typical weight for a male of 200–400 kilograms. “This Columbia river salmon seems to fatten them up bigger and better than anything we’ve ever seen.”
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5 Comments
Add CommentIf the problem is that the lions eat the salmon waiting to climb the ladder, wouldn't it be possible to create a refuge behind a fence that is passable by the fish but not by the lions? There's a big difference in sizes, and it seems possible to install such a fence near the entry to the ladder to give the fish the possibility to evade their predators while waiting.
Reply | Report Abuse | Link to thisJust one more reason to totally do away with all government employees and start all over again. Federal agencies are a freight train that can't stop because it has no driver and no brakes. the only way to protect any of our wildlife is to have smart normal people do it. They would just do what needs to be done. We can't protect one species and manage all the others. It can't work. Billions of dollars are wasted on salmon if they let these sea lions come eat em all at a man made barrier. NOAA. You are a bunch of overeducated / stupid ?lazy / computer addicted morons. Get to work. Do something other than email and go to meetings
Reply | Report Abuse | Link to thisThe sea lions are not the problem. In reality the sea lion are only eating between 1% and 4% where as the fisherman are killing 14%-16% and the dam is killing around 14%. In addition, there is an aggressive species of fish that was introduced into the river that is eating the salmon roe. The sea lions are not the problem but rather the scapegoat.
Reply | Report Abuse | Link to thisHow more I know humans, more I like Animals
Reply | Report Abuse | Link to thisFisherman in Oregon/Washington are required by law to only harvest hatchery raised adipose fin clipped salmon. Only native Americans are allowed to harvest wild Chinook salmon according to treaties made with the government back in 1855. The 14%-16% of fish harvested your stating
Reply | Report Abuse | Link to thisis inaccurate due to most of those fish being hatchery born and not wild. I do however agree that the dams are the biggest problem that wild Chinook face.