You would have thought that if you wanted to keep a fish out of a particular stream, you could just block the channel with an underwater screen. Unfortunately, it's not that simple. Humans are constantly erecting barriers to alter the course of nature, but too often, wildlife runs headlong into the 'detour' signs.

We could prevent such disastrous collisions if we learned enough about wildlife before trying to mess with it. Joseph Cech and his colleagues in the Department of Wildlife, Fish and Conservation Biology at UC Davis have immersed themselves in the details of fish biology in their attempt to solve a current problem in the Sacramento - San Joaquin Delta.

Management of our rivers and delta requires that we regulate the water through damming and releasing, channeling and diverting. At the same time, we must direct the movements of our fish if we want to keep them out of troubled waters. To this end, wildlife managers have erected fish screens at large diversions like the California Aqueduct that takes some of our water to southern California. The problem with this method is that small, delicate fishes that are weak swimmers get swept against the screens and "stuck" there. This injures them and increases their vulnerability to predators.

The Delta smelt, for example, is about two to three inches long, and exists only in California's Sacramento-San Joaquin Delta. During the early 1980's its numbers declined so drastically that it is now listed as a threatened species. It seems that fish screens erected at diversions are partly to blame for the smelt's predicament.

The problem for this species is that present standards for fish screens were modeled on stronger swimmers such as salmon or shad. This was before the decline of the Delta smelt, when the species was abundant and no one thought we had to worry about it. Now, researchers at UCD want to develop screens that would be kinder to the smelt and other small vulnerable fishes such as the juveniles of splittails (a native) and chinook salmon (endangered).

The problem is complex. Whether or not a fish gets stuck on a screen depends on a combination of factors such as size, speed of current, swimming speed, and amount of light. Cech and his team have to examine the performance of fish under a variety of conditions. How do you get fishes to perform?

Answer - put them in a treadmill. Professor Cech and fellow fish biologists, Tina Swanson and Cincin Young, teamed up with Professor Lev Kavvas from Civil and Environmental Engineering.

The result is the Fish Treadmill, a 20'- diameter tank containing a circular swimming channel whose inner edge is a fish screen. The scientists can control two current speeds: one that flows against the screen, the "approach speed", and one that flows across the screen. They can also change the lighting to simulate daytime and nighttime, as well as water temperature to simulate different times of year.

Then, under various combinations of conditions, researchers record the behavior of fishes in the Treadmill, including how fast they swim, where they swim, number of times they hit or get stuck on the screen, and how often they die as a result.

The work is still in the early stages, but experiments on the Fish Treadmill have already produced valuable information. For example, death rates were related to how often fishes hit or got stuck on the screen, and the most important influence on this was the "approach speed" of the current. Small species like the Delta smelt require relatively slow currents if they are to avoid getting stuck. In the real world beyond the Fish Treadmill, the approach current can be altered by the size of the screen: the bigger it is, the more water flows through it, the slower the current.

The findings from this research, which is funded by the California Department of Water Resources, will be used to guide the design and operations of more smelt-friendly screens at large water diversions,

This project is not just about saving a three-inch fish. It is about restoring and maintaining the biological richness of the Delta. To us, the term, Fish Treadmill, might conjure up Larson-esque images of spandex-clad salmon sweating it out in a gym. But for researchers at UCD, it means saving California's natural heritage through a deeper understanding of fish behavior and biology.

© Kelly Stewart

Dept. of Anthropology, University of California, One Shields Av., Davis, CA 95616
e-mail: kjstewart@ucdavis.edu

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