EPOW - Ecology Picture of the Week

Fight for the Fish

California Sea Lion (Zalophus californianus), Family Otariidae
Bonneville Dam, Columbia River, Washington-Oregon border, USA

Explanation:  This is a story of competition for a highly desired natural resource.

The star of this week's EPOW episode is a lone California sea lion who has traveled the 145 river miles from the mouth of the Columbia River to this location.  

  
Why?  

There be fish here!  

More precisely, tasty salmon, returning from the ocean on their final life's journey upstream to spawn and then die.  

Here, the fish pile up in front of mighty Bonneville Dam that spans the mightier Columbia River that separates the states of Washington and Oregon in the Pacific Northwest U.S.  

Located 40 miles east of Portland, Oregon, Bonneville Dam was constructed to provide massive amounts of hydroelectric power to many cities.  Back in 1806, Lewis and Clark's expedition camped upstream along Tanner Creek on the Oregon side.  Now the Bonneville Fish Hatchery and Sturgeon Center can be found near the dam site.  
  

  
 So what's all the fuss with the hungry sea lion?  
  

  
For many years, California sea lions -- at times in large numbers -- have congregated along the fish ladders at the base of the dam, snatching large numbers of salmon and steelhead fish.  This has been viewed as a major threat to some of the fish runs that are protected under the Endangered Species Act.  

But the Marine Mammal Protection Act also protects the sea lions.  Quite a quandary.

Over the past decade and a half, wildlife managers from federal, state, and Tribal agencies and communities have tried to chase the sea lions away and otherwise institute deterrents, but to little avail.  Starting in 2008, federal decree allowed the killing of sea lions.  Recent control activities can be followed on this Oregon Department of Fish and Wildlife website.  
  

  
Mostly, the agencies prefer to trap and relocate the sea lions, and much of their control activities have focused on nonlethal trapping and translocation.  By trapping and release, the agencies can tag individuals and better understand their movement patterns, and if, when, and how often they may return to the dam site.  

One final note.  Reducing and removing California sea lions at the dam site may be providing an unexpected opportunity for another competitor -- the Stellers sea lion -- to fill in the gap.   As has often been stated, at times nature does seem to abhor a vacuum ...