The states of Oregon, Washington and Idaho have permission from NOAA Fisheries to remove and even kill sea lions that eat substantial numbers of salmon and steelhead on the Columbia River near Bonneville Dam.Is removal of sea lions, lethal or otherwise, effective?
A recently published study examined whether removing sea lions that have learned to snatch salmon from Bonneville fish ladders was effective at preventing the behavior from being socially transmitted.
In 2015, sea lions consumed nearly 10,000 adult spring Chinook, which is more than 3 percent of the returning adult fish. And since 2013, the number of sea lions in the area and their consumption of protected salmon have increased significantly.
The research, published Dec. 14 in the Proceedings of the Royal Society B: Biological Sciences, concluded that relocating and killing sea lions may be slowing the transmission of the salmon-preying behavior.
But sea lion removal would have worked better had it been done as soon as the behavior was discovered--before a few sea lions had the opportunity to teach others the fishing technique, the researchers said.
The authors, scientists from the Pacific Northwest, used epidemiological methods to track the passing of information among sea lions on how to catch salmon.
Using models designed to study the transmission of disease to prevent epidemics is new to fish and wildlife management.
The study abstract explained what epidemiological methods can contribute, "Socially transmitted wildlife behaviours that create human-wildlife conflict are an emerging problem for conservation efforts, but also provide a unique opportunity to apply principles of infectious disease control to wildlife management."
"Epidemiological analyses offer a promising tool to understand and control socially transmissible behaviours," the researchers said.
Since the removal effort on the Columbia River started in 2008, the three states relocated and/or euthanized 166 animals. Another 59 California sea lions were removed in 2016, a record number in a single year.
The states may euthanize sea lions to deter individual animals habitually preying on salmon if no permanent holding facility, such as an aquarium, can be found. -Laura Berg
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