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California Freshwater Shrimp cont.

Napa River and its Garnett Creek tributary, Keys Creek (a tributary of Walker), and Redwood Creek (a tributary of Jonive). A total of eleven separate stream systems (sixteen streams) are inhabited, but the future of the species is still uncertain. Thousands of shrimp live in Lagunitas, Salmon, and Blucher Creeks, but even in these streams, a single toxic spill could wipe out the bulk of the population.

The shrimp are found within stream pools, in areas away from the main current, where there are often undercut banks, exposed root systems, and vegetation hanging into the water. They need all of these habitat components for survival. The best habitats have a mixture of willow and alder trees. Some of the shrimp streams are completely enclosed with streamside vegetation, while others have just a few scattered trees along the banks. In the latter case, dark, shaded water is necessary to help protect them from visual predators. Too little or too much water in the stream can present a problem. Most shrimp are found in areas that are one to three feet deep. For the most part, only the sides of the pools are utilized. Shrimp avoid the pool bottoms, and are only found there after being disturbed, or when populations are especially high.

Filamentous blackberry roots sprout from stems wherever they extend beneath the surface, and form an ideal refuge most of the year. At times of higher flow, though, these roots tend to be lifted out of the stream by the rising water, and left in a useless tangle above the bank when the water recedes. Dense, beard-like willow roots, often extending more than a foot out into the water, are more dependable. Alders provide both short filamentous roots, and the coarser hard roots that support the stream banks. As the bank soils partially erode from the force of the current, a network of the rigid roots is exposed. Overhanging the undercut banks, these roots reduce the erosive power of the water, and protect the banks from further damage. The roots form a useful highway system for the shrimp. During the heavy flows of water accompanying storms, the shrimp abandon the softer vegetation and travel close to these sturdy roots, or even