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.三一河恢复计划（Trinity River Restoration Program, TRRP）的核心目标之一，是通过各类修复举措维持并优化区域内野生动物种群的存续状态与种群规模。对于两栖爬行动物物种（herpetological species）而言，山麓黄腿蛙（foothill yellow-legged frog）与西部池塘龟（western pond turtle）已被确定为监测工作的重点关注物种，因其均被列为加州关注物种（California state-listed Species of Concern）。为此，此前已有大量研究工作聚焦于阐明这两个物种的分布范围与种群动态，研究区域覆盖主三一河，以及作为对照种群的南三一河——后者或可代表水坝修建前的原始种群状态。此类研究揭示了两条河流间各物种生活史特征的显著差异，这类差异或由主三一河的环境条件所导致。以西部池塘龟为例，相较于南三一河种群及本区域其他西部池塘龟种群，主三一河的西部池塘龟呈现出生长速率缓慢、成体体型偏小、年繁殖力更低，以及性成熟年龄更晚的生活史特征。对于山麓黄腿蛙而言，主三一河的卵块密度较南三一河低一个数量级；此外，主三一河的蛙卵块还会因水坝泄水的时机与水量，面临被水流冲刷的风险。三一河恢复计划正着力解决上述问题：一方面会将水资源管理决策对上述物种的影响纳入决策考量范畴，另一方面在旨在改善鲑科鱼类育幼栖息地的河道修复工作中，也会充分纳入这些物种的栖息地需求。