Foothill Yellow-Legged Frog (Rana boylii) Monitoring and Assessment Data from the Trinity River, California (2013-2017)

A key objective of the Trinity River Restoration Program (TRRP) is maintaining and enhancing other wildlife populations through the restoration initiatives. For herpetological species, the foothill yellow-legged frog and western pond turtle have been identified as important species on which to focus monitoring efforts due to their status as California state-listed Species of Concern. As a result, considerable prior effort has focused on understanding the distribution and demography of these species, both on the main Trinity River and on the South Fork Trinity River as a comparison population (potentially representing pre-dam population status). These studies have highlighted differences in life-history traits of each species between the two rivers that may be due to conditions of the main Trinity River. For western pond turtle these traits include slow growth rates, smaller adult sizes, lower annual fecundity, and later age at maturity in comparison to South Fork Trinity River and other western pond turtles in the region. For foothill yellow-legged frogs, densities of egg masses are an order of magnitude lower on the main Trinity River in comparison to the South Fork Trinity River. Egg masses on the main Trinity River are also vulnerable to scour depending on the timing and volume of water released from the dam. TRRP is working to address these issues by including consideration of the impacts of water management decisions on these species, as well as taking habitat requirements into account in their channel rehabilitation work that is geared towards improving salmonid rearing habitat.