In partnership with Gulf South Research Corporation, FISHBIO conducted environmental DNA (eDNA) and habitat surveys in 2018 and 2019 to determine the seasonal presence of endangered Southern California steelhead in the San Mateo Creek and Santa Margarita River watersheds. Steelhead may enter these watersheds to migrate to their spawning grounds after rainfall events, which can increase river flows enough to breach seasonal lagoons and connect streams to the ocean for short periods of time. These events typically increase water levels and turbidity, which present challenges to conventional methods of fish monitoring, especially for rare species.

To overcome these challenges, FISHBIO conducted bi-weekly eDNA surveys to determine whether Southern California steelhead use the monitored streams. We used a Smith-Root ANDe system to pump water over a microfilter that retains the minute fragments of eDNA that animals shed into their environment. After sample collection, the filters were preserved and sent to a laboratory for processing. eDNA surveys were paired with visual surveys to record the presence of other fish species in the streams of interest. Streams with confirmed presence of steelhead outside the immediate project area were also sampled as part of the study to provide a positive control for eDNA surveys. FISHBIO staff also conducted a habitat assessment of the migratory corridor at the primary survey site, which consists of several miles of periodically dry streambed between stream headwaters and the ocean estuary. These surveys were intended to identify and map potential migration barriers, holding water, and stream channel types.

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