Are the Kootenai River white sturgeon bad parents?
| June 24, 2010 9:00 PM
Ever since studies of white sturgeon spawning in the Kootenai River began in the early 1990s, researchers have wondered why sturgeon were found to be spawning over sandy bottoms.
Better habitat composed of cobble and gravel is found above Bonners Ferry. Sand makes a poor nursery for white sturgeon eggs, because a quarter inch of it can suffocate a healthy egg.
Young wild sturgeon are rare in the Kootenai River. So despite the fact that sturgeon spawn, it is apparent that sturgeon egg survival is very poor.
So are Kootenai River white sturgeon bad parents? The answer is no. They are good parents, it's just that the habitat of the Kootenai River has changed so much since Libby Dam was built that what was once good habitat for sturgeon spawning is now very poor habitat.
The biology and science behind white sturgeon spawning in the Kootenai River has been an ongoing challenge to the Idaho Department of Fish and Game for more than four decades. It all began in the late '70s shortly after Libby Dam was built. Studies that began in the 1970s found that white sturgeon in the river were not reproducing successfully. The dam had begun regulating the flow of water in the river so that flows during the spring, when sturgeon spawned, were only about a quarter of historic flows before the dam was built.
In 1994, the fish was listed as "endangered" by the U.S. Fish and Wildlife Service. One attempt at recovery was adding additional water flow in the spring to encourage white sturgeon to spawn. Fish and Game studies indicated white sturgeon were spawning downstream of Bonners Ferry, but the habitat was unsuitable as a nursery area for white sturgeon eggs. Better habitat was upstream of Bonners Ferry. Researchers questioned why white sturgeon would spawn in an area with unsuitable nursery habitat (sand) when the preferred habitat would be cobble and gravel.
Two independent studies were conducted to test whether sturgeon would spawn above Bonners Ferry, and what might attract them to the cobble and gravel habitat. In the first study, adults were transported above Bonners Ferry for two years to the better spawning habitat. In the first year, a male and female hung out for one day and eggs were found nearby.
But the two adults soon moved downstream and joined others in the traditional location. In this study, sturgeon transported to the cobble and gravel areas moved frequently and spent little time in the better habitat. Many moved out of the river completely to Kootenay Lake, while some joined others in the traditional spawning location.
In a second study, 70 sturgeon were fitted with transmitters over five years. Sophisticated receivers recorded their movements throughout the river. It was anticipated that any movement of sturgeon could be tied to environmental conditions. After countless hours of study it was determined there was very little movement to cobble habitat above Bonners Ferry. What little movement did occur to Bonners Ferry was determined by scientific analysis to be merely random. No environmental predictor or cue could be found.
Fish and Game researchers were slowly beginning to understand the biological mystery of white sturgeon. This was accomplished during the late 1980s and early 1990s by attaching radio transmitters to hundreds of adult fish ready to spawn and then looking for eggs in suspected spawning areas.
Key questions to be answered were: Where did adults go to spawn? Where were their eggs found? And, when did sturgeon spawn in relation to water temperature and river flows?
Using the telemetry information, researchers found that female sturgeon were predictable in their movements, but the males were not. After the water temperature in the spring increased to about 47 degrees, spawning took place and eggs were found over sand substrates in specific locations year after year. Water temperature was determined to be the most important factor.
All of the spawning took place downstream of Bonners Ferry.
Researchers also found the sand substrate was very mobile, forming shifting underwater sand dunes that likely suffocated the eggs by burying them. Other white sturgeon studies around the West showed that cobble and gravel was the preferred substrate for spawning. So why would the white sturgeon parents spawn year after year in the same locations in sand habitat?
Fish and Game researchers realized it was important to examine not only the biological science of the fish, but the physical processes in the Kootenai River as well. So, they teamed with river scientists from the U.S. Geological Survey. The USGS scientists brought with them the technology to track sediment transport, the configuration of the river, velocities in the river, profiles of the river bottom, river substrate and more.
With this information, the USGS scientists were able to make models of the river and predict how it would respond to various flows. This information was combined with the Fish and Game sturgeon spawning information. It was then discovered that the white sturgeon were cueing on locations of increasing river velocities in deep water. Regardless of the flows, these reference points were always in the same location. It was also learned that there was cobble and gravel buried under the sand in those same locations.
Unfortunately, the modeling also indicated that the only flows from Libby Dam suitable to scour and clean those cobbles and gravels were so high they would compromise public safety and impact agriculture. To test the model would also cause alarm and unsafe conditions.
In 2006, however, an unpredicted flood exposed the cobble and gravel - confirming what the researchers had suspected all along. The fish were good parents and were spawning in traditional locations. But limitations of water flow management had changed the habitat. In spring, the river flows controlled by the dam do not have the force to clean the cobble and gravel. Only river flows such as those that existed before the dam would restore the habitat and promote successful sturgeon spawning.
So what can be done? One major step is to physically alter the river to conform better to its new flow regime resulting from Libby Dam. This would give the river the power to clean the spawning locations and expose the cobble and gravel before sturgeon spawned, without flooding. Alternatively, physical structures and suitable spawning habitat could be added in key locations.
The Kootenai Tribe of Idaho, with the support of Idaho Fish and Game, is sponsoring such a river restoration project. This project has a long way to go but is making progress.
If we want the Kootenai River white sturgeon to rebound, it will take just such a project to bring them back from spawning failure to spawning success.
Vaughn L. Paragamian is the fisheries research biologist in the Panhandle Region.