In the winter of 2008 a sonar survey of the area below the spillways of Bonneville dam revealed what appeared to be a massive pile of rubble. The operator of the dam, the U. S. Army Corp of Engineers, was very concerned that part of the dam structure might be failing.
The Corps called on the 86th Engineer Dive Team to inspect the 'rubble'. The 86th is a Fort Eustis, Virginia, based team of US Army divers that stand ready to take on challenging underwater assignments wherever they are needed.
On February 19th, the 86th lowered a remotely operated submersible (ROV) equipped with a video camera to inspect the suspected damage. Much to everyone's surprise, when the video from the cam was viewed, the suspected pile of 'rubble'
Ash Creek Images
Photographs of the West by Doug Gorsline
Thousands of Sturgeon Gather Below Bonneville Dam's Spillways in 2008
Michael Parsley, a research fisheries biologist from the U.S. Geological Survey's Columbia River Research Laboratory in Cook, Washington conservatively estimated that the mass contained more than 60,000 sturgeon, which would be a small but significant fraction of all the white sturgeon in the lower Columbia River. In 1999, the Oregon Department of Fish and Wildlife estimated that there were 359,000 sturgeon just between 36" and 72" below Bonneville.
No one knows why the sturgeon congregated in such a large, dense school, but it may be part of an energy conservation strategy. During the winter months, little if any water is passed over the spillways; most of the water is directed through the 2 powerhouses. The water temperature was low at the time the school was discovered; 34 to 35 degrees Fahrenheit. The large area with low current in front of the spillways may be a very attractive place for white sturgeon to accumulate and winter with a minimum expenditure of energy.
Others have speculated that it may be a defensive schooling strategy by the sturgeon to protect themselves from Stellar sea lions and California sea lions which have accumulated in the area below the dam in increasing numbers over the last few years. The sea lions mainly attack the spring chinook runs, some of which are on the endangered species list, but witnesses also saw over 600 sturgeon taken this year, mainly by Stellar sea lions.
On the other hand, there are very few sea lions at the dam at the time the video was made. By the time the sea lions and the salmon began to arrive in numbers, the Corps began to run water over the spillways and the sturgeon dispersed.
By May and June, there is no place to rest under the spillways.
Sturgeon provide an important sport and commercial fishery in the lower Columbia River. As other fish stocks have collapsed, sturgeon populations have remained healthy. Only sturgeon between the lengths of 42" to 60" may be taken by sports fishermen. This allows smaller fish to grow to maturity. The very large fish are protected because they are responsible for most reproduction capacity.
There are many licensed guides on the lower Columbia River that specialize in sport sturgeon fishing. Most of them operate large, comfortable jet boats and many of them have decades of experience.
Bonneville Dam is also the home of the historic Bonneville Hatchery and Herman the Sturgeon, a rather famous white sturgeon of whom I was lucky enough to shoot a pretty good photo one day. Herman's pond holds a number of other sturgeon, large and small.
Much of the information in this article was compiled from an article that appeared in the Portland, Oregon newspaper The Oregonian on May 16, 2008.
turned out to be what Dennis Schwartz, a fisheries biologist with the Corps of Engineers, called a "big sturgeon ball." Sturgeon up to 14 feet long were observed in this "ball".
