Zostera marina is a seagrass species, commonly known as eelgrass, that is found on both coasts of the United States, as well as in Europe. Unfortunately, Zostera is disappearing all over the place, including right here in New York. This could have devastating impacts on animals that rely on eelgrass as foraging grounds, or, as is the case with scallops, use it as a refuge from predation. This is its story, as seen through the eyes of an aspiring graduate student...

Thursday, September 30, 2010

Sea lions devastating threatened fisheries...

Another article about the devastation sea lions are causing on fish stocks on the west coast.  Only this time, the focus isn't on salmon.  Sea lions have been congregating at passage points on dammed rivers on the west coast for years, and have been consuming salmon as they enter these passages to return upriver to spawn.  This has been in the news for quite some years, since around 2005, and have continued to receive some level of attention in the public eye, where sea lions are being killed to save salmon, even while salmon experts call for other options.It has also received attention in scientific communities,  to the point where large dollars have been invested to examine the exact impacts on salmonid populations by the increase in sea lion and seal populations

However, the new article as it appeared today talked about sea lions now beginning to consume female sturgeon as they reach these dam points.  This is a relatively new idea.  It appeared in a Northwest Council report about strategies to address the sturgeon population.  Not sure if this is a prey switching situation, as my recent online search hasn't turned up many results.  But this was a finding in the above report:

"Limiting Factor:  Marine mammal predation
Primary Threat:  Predation by sea lions on sub-adult, adult, and spawning-size white sturgeon below Bonneville Dam.  Oregon and Washington Department of Fish and Wildlife staff have directly observed more that 150 white sturgeon being preyed upon between January 2006 and May 2007, more than 60% of which were spawning-size fish.  These are actual numbers based on direct observations during other sampling activities, not a targeted sampling effort; the actual number of white sturgeon taken by sea lions is likely much higher.  Steller sea lions appear to be especially effective in preying upon large, spawning-size sturgeon, and may selectively capture fish of this size.
Strategy:  Conduct non-lethal hazing actions on the Columbia River to deter California and Steller sea lions from feeding on white sturgeon. 
Measures: Hazing with acoustic and percussive devices, flares, and rubber bullets has been shown to be relatively effective in deterring predation on white sturgeon by Steller sea lions in the area immediately below Bonneville Dam.  Hazing has been an ineffective deterrent for California sea lions.  Steller sea lions have been appearing earlier in the year each year since first sited near Bonneville Dam.  Hazing to protect sturgeon should begin when Steller sea lions are first sited near the dam in each year.  In 2007, hazing began in mid-December from Bonneville Dam downstream approximately six miles to Navigation Marker 85.  Hazing will take place four days a week during daylight hours.  Separate from the hazing efforts, fishery managers from Washington, Oregon and Idaho are seeking federal approval to use lethal means to remove individual California sea lions from below Bonneville Dam that prey on white sturgeon as well as Chinook salmon and steelhead listed for protection under the federal Endangered Species Act (ESA).  Efforts to date have focused on the area immediately below Bonneville Dam, but predation by sea lions on white sturgeon is known to occur throughout the lower Columbia River."

Well back to the article, its brief, but basically it talks about observations of the sea lions eating sturgeon on the Columbia River.   And while this isn't being observed at the Fraser River yet, given the still increasing sea lion and seal populations, its probably only a matter of time.

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