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Scott Wilson

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Stanislaus River Report


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Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept. of Fish and Game

California Tiger Salamander

Ambystoma tigrinum californiense

Category 2 Candidate for listing by the U.S. Fish and Wildlife Service and California Department of Fish and Game "Species of Special Concern"


Life History

The California tiger salamander is a large salamander measuring 7 to 15 inches in length and is distinguished from other salamanders by spots and bars of white, cream, or yellow on a black background. This salamander has small eyes, a broad and rounded snout, and tubercles on the underside of the front and rear feet (Stebbins 1985).

The California tiger salamander typically inhabits grassland and oak woodland habitats below 1,500 feet which have scattered ponds, intermittent streams, or vernal pools. Shaffer et al. (1993) determined that pond type, size, and turbidity affected tiger salamander distribution; vernal pools covering more than 250 square feet with fairly turbid water provide the best habitat. Additionally, a significant inverse association of California tiger salamanders with predatory fishes and bullfrogs has been found. The reason is that larval salamander fall prey to predatory fish and adult bullfrogs, in addition larval bullfrogs compete with salamanders for food (Shaffer et al. 1993).

Tiger salamanders estivate in rodent burrows throughout the summer and emerge after the first few sustained rain storms in November. Rainfall is important to the maintenance and formation of breeding ponds and also triggers adult migration to breeding ponds. Adults will migrate up to 3,300 feet from estivation sites to breeding ponds. The breeding season extends from December through February with females laying numerous small clusters of eggs on submerged and emergent vegetation (Stebbins 1972). Adults remain in breeding ponds for several days before exiting to forage in terrestrial habitat.

Adult and terrestrial juveniles forage on earthworms, snails, insects, fish, and small mammals by utilizing sit-and-wait tactics to capture their prey (Lindquist and Bachmann 1980, Stebbins 1972). Small aquatic larvae forage primarily on zooplankton while larger larvae forage on zooplankton, amphipods, mollusks, and insect larvae (Dodson and Dodson 1971).

Findings and Conclusions

Current threats to the continued existence of the California tiger salamander include habitat loss due to increased urbanization, conversion of native grasslands to agriculture, introduction of predatory fish in known breeding ponds, introduction of bullfrogs, rodent control which reduces the availability of summer estivation sites, development of roads between breeding ponds and terrestrial habitats and associated automobile deaths, and the introduction of other tiger salamander species which could potentially result in genetically inferior hybrid salamanders.

The Stanislaus River itself is not considered potential habitat because flows are variable and frequently too heavy to be a reliable breeding area. There is, however, tiger salamander habitat along the Stanislaus River corridor within the grasslands of all three reaches. One sighting of this species was recorded in 1975 near the town of Oakdale. More recently, BioSystems (1994) reported tiger salamander larvae found in several locations north of Oakdale.

Any project involving the Stanislaus River which affects the adjacent grasslands or open areas within any of the three reaches could potentially affect this species and further surveys would be needed.