USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
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Research Topics Wildlife & Fish

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Herpetology in Trinity River, California
Effects of Damming on Two Herpetofaunal Species of a Riverine Ecosystem

We investigated the effects of the Trinity River's Lewiston Dam on foothill yellow-legged frogs and northwestern pond turtles from 1991 to 1994. Habitat use and reproductive ecology were compared for dammed and undammed forks.

Trinity River Foothill Yellow-legged Frog with Egg Mass Northwestern Pond Turtle Juvenile

In the dammed fork, reduced water flows and vegetation encroachment resulted in channelization and decreased the quantity of open river gravel bars and associated shallow water habitats. Breeding habitat for foothill yellow-legged frogs and rearing habitats for juvenile northwestern pond turtles was reduced by 94% from pre-dam levels.

High-flow releases from the dam during the frog breeding season resulted in loss of eggs in some years. Egg laying activity following releases was insufficient to recover the losses.

Habitat complexity was lower on the dammed than undammed fork.

Water temperatures were markedly lower in the dammed fork compared with the undammed fork. Low temperatures retard the development of frog eggs and larvae and increase the energetic demands on turtles.

We recommend that the timing and magnitude of releases from this dam be based on natural precipitation cycles (see Grass Valley Creek hydrograph) so that annual reproduction in foothill yellow-legged frogs is not disrupted year after year, and suitable habitat for both species is not further degraded.

Pond Turtle Envirogram

Western Pond Turtle (Actinemys marmorata) envirogram (Andrewartha and Birch, 1984) of interactions and relationships of biology, resource needs, direct and indirect impacts, and conservations options relative to life stages and environmental requirements. By Donald T. Ashton and Hartwell H. Welsh.