Type: report

Article abstract: From 2002 to 2004, California State Parks contracted with the U.S. Geological Survey to conduct daytime habitat evaluation and focused nocturnal surveys to determine the distribution of suitable habitat and presence of arroyo toads (Bufo californicus) within Cuyamaca Rancho State Park (CRSP). The 2002 and 2003 surveys documented breeding populations of arroyo toads at four high-quality sites along the Sweetwater River, but the effects of the Cedar Fire in late 2003 on these populations were unknown. The purposes of the 2004 surveys were to determine if there were changes in the distribution of arroyo toads and arroyo toad habitat as a result of the Cedar Fire, and to determine fire severity levels at the four previously known high-quality habitat locations. To accomplish this, we used daytime habitat evaluation surveys, fire severity transects, and nocturnal presence surveys. Each 250-m stretch of the river was re-evaluated based on the presence of key arroyo toad habitat characteristics: 1) the channel substrate and banks being predominately composed of depositional sand, 2) flat, exposed sandy terraces immediately adjacent to the channel, and 3) channel braiding. Furthermore, the reaches were surveyed diurnally and nocturnally for all life history stages of the arroyo toad and other riparian-associated animal species. Of a total 17.0 km (10.6 mi) of riparian habitat surveyed, 7.8 km, or nearly half of the river within CRSP, was rated as high- (3.7 km) or good-quality (4.1 km) habitat for arroyo toads. Arroyo toads (particularly the immature stages) were abundant in the lower third of the Sweetwater River, found virtually continuously along a 5.2-km stretch of river. Breeding individuals and large numbers of young were also detected in the middle of the river within CRSP, thus documenting the presence and breeding of arroyo toads in all four sites from the previous two years. In addition, we recorded a large adult female at the highest known elevation (1,354 m; 4,442 ft) for arroyo toad occurrences in the Sweetwater River watershed, in a severely burned, dry portion of the river several kilometers upstream from the nearest surface water. Chytridiomycosis, a major infectious disease affecting amphibians, was detected in one arroyo toad and one Pacific treefrog which were collected dead during the surveys, possibly representing the first cases of the pathogen in amphibians in the watershed. According to the fire severity transect