San Diego Management & Monitoring Program


Assessing the Risk of Loveland Dam Operations to the Arroyo Toad (Bufo californicus) in the Sweetwater River Channel, San Diego County, California

Type: report

Article abstract: The purpose of this study was to provide a risk assessment of the short-term and long-term effects of Loveland Dam operations on arroyo toad (Bufo californicus) reproductive success and population viability. Results of this study will be used in the development of the Sweetwater Authority Subarea Plan of the Joint Water Agencies Subregional Natural Community Conservation Planning (NCCP) program and will be used in the process of gaining scientific justification for the United States Fish and Wildlife Service (USFWS) and California Department of Fish and Game (CDFG) incidental take permits associated with the Sweetwater Authority Subarea Plan (Fleury 2001). The goal is for Sweetwater Authority to maintain flexibility in the management of their reservoirs while sustaining arroyo toad populations within the system (Fleury 2001). Historical arroyo toad breeding, weather, hydrological, and Loveland Dam release data were used to examine the risk associated with the short-term and long-term effects of Loveland Dam operations on arroyo toad reproductive success and population viability. Dam releases during the arroyo toad breeding season are the biggest concern for reproductive success and the focus of this risk assessment. Using historical breeding occurrence data, rough upper and lower bounds for arroyo toad cohort loss due to controlled dam releases during the arroyo toad breeding season were estimated. In the analysis, risk due to dam releases was found to be the highest in early March to late July when the greatest loss of egg masses, larvae and metamorphs was estimated to occur, with the upper bound ranging from 28% to 63% of the entire year's cohort. Over time, repeated loss of cohorts due to dam releases can decrease population viability, but further study is required to determine the exact risk. Simply avoiding controlled releases during the arroyo toad breeding season, especially from March to late July, will greatly reduce the risk to arroyo toad reproductive success and population viability. In addition, several other possible risks to arroyo toad reproductive success as a result of dam operations were qualitatively examined. These included the effects of dam releases concurrent with rain or spill events, the effects of dam releases during wet and dry years, the effects of the intensification and lengthening of drought periods and the effects of the degradation of arroyo toad breeding habitat from the increase in vegetative

Number of pages: 63

Authors: Madden-Smith, Melanie; Atkinson, Andrea; Fisher, Robert N.; Danskin, Wesley R.; Mendez, Gregory O.;

Year: 2003

Prepared for: Sweetwater Authority;

Prepared by: U.S. Geological Survey, Western Ecological Research Center;

Keywords: arroyo toad; endangered; Loveland Dam; NCCP; risk assessment; Sweetwater;

Species: Arroyo toad

Projects: