Occurrences of Steelhead Trout (Oncorhynchus mykiss) in southern California, 1994-2018

Abstract

Observations of federally endangered Southern Steelhead Trout (Oncorhynchus mykiss) were compiled for the southern California Distinct Population Segment (DPS) that extends approximately 500 kilometers from the Santa Maria River (Santa Barbara County) south to the Mexican border. Existing monitoring programs and anecdotal observations documented 177 adult Steelhead in the past 25 years. The level of monitoring effort and technology used varied by watershed and year. Thus, the low numbers of adult Steelhead observed during the past 25 years provides relative abundance and distribution documentation of occurrences but likely underestimates the abundance of adult Steelhead throughout the DPS. The patchy distribution observed suggests that fish are opportunistically entering creeks and river mouths based on available hydrologic passage opportunities associated with higher rainfall years. Given the extremely low numbers of anadromous adults, long recovery timeline, future uncertainty with respect to climate change, and a multitude of anthropogenic factors, additional conservation actions including state and federal protection of resident O. mykiss are recommended to increase the likelihood of the continued existence of the species within the DPS. Additional focused monitoring, research, and implementation of recovery actions are needed to expand our knowledge of southern California Steelhead distribution and abundance.

Keywords

• anadromous adults
• rainbow trout
• southern california
• southern steelhead