Herpetological monitoring and assessment on the Trinity River, Trinity County, California—Final report

Abstract

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov/ or call 1-888-ASK-USGS (1-888-275-8747).For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Tables Table 1. Multi-season occupancy models describing the probability that a site was occupied by breeding foothill yellow-legged frogs (Rana boylii), Trinity River, Trinity County, California, 2013-15 AbstractThe primary goal of the Trinity River Restoration Program is to rehabilitate the fisheries on the dam-controlled Trinity River. However, maintaining and enhancing other wildlife populations through the restoration initiative is also a key objective. Foothill yellow-legged frogs (Rana boylii) and western pond turtles (Actinemys marmorata) have been identified as important herpetological species on which to focus monitoring efforts due to their status as California state-listed species of concern and potential listing on the U.S. Endangered Species List. We developed and implemented a monitoring strategy for these species specific to the Trinity River with the objectives of establishing baseline values for probabilities of site occupancy, colonization, and local extinction; identifying site characteristics that correlate with the probability of extinction; and estimating overall trends in abundance. Our 3-year study suggests that foothill yellow-legged frogs declined in the probability of site occupancy. Conversely, our results suggest that western pond turtles increased in both abundance and the probability of site occupancy. The short length of our study period makes it difficult to draw firm conclusions, but these results provide much-needed baseline data. Further monitoring and directed studies are required to assess how habitat changes and management decisions relate to the status and trend of these species over the long term.

Identifying drivers of population dynamics for a stream breeding amphibian using time series of egg mass counts

“…Time series of egg mass counts were not continuous for some streams, but state‐space models that underlie MPVA (see below) allow for the use of incomplete time series by inferring the abundance of egg masses during years without surveys. Egg mass surveys came from a variety of sources, including long‐term studies of the ecology of R. boylii (e.g., Kupferberg et al, 2012; Wheeler & Welsh, 2008), monitoring programs for populations affected by dams (e.g., Pacific Gas and Electric Company, 2020; Snover & Adams, 2016), and focused studies on the effects of environmental conditions on breeding (e.g., Gonsolin, 2010; Lind et al, 1996; van Hattem et al, 2021; Wheeler et al, 2015). We treated reaches of the same stream as a single population if they were directly connected without any barrier (e.g., a dam, lake, or reservoir) between the reaches and were surveyed using the same methods by the same research group.…”

“…When demographic data are lacking, counts from regular population censuses can be used to estimate population growth (Molano-Flores & Bell, 2012). Count-based models have been applied to wildlife populations for the past four decades; these models can incorporate density dependence (Dennis & Taper, 1994), observation error (Staples et al, 2004), and incomplete sampling (Leasure et al, 2019). Given the greater spatial and temporal coverage of count data, count-based MPVA has the potential to reveal the drivers of population dynamics for many amphibian species.…”