Despite the presence of impassable migration barriers and urbanization, steelhead continue to attempt to migrate upstream in creeks like Mission Creek in the City of Santa Barbara.

This NOAA Technical Memoranda was produced by NOAA-National Marine Fisheries Service, Stoecker Ecological, and the Watershed Institute. The report assesses the occurrence of anadromous O. mykiss in each coastal basin from Monterey Bay south to the Mexican border. Ninety-two basins were identified and historic occurrence of O. mykiss was estimated in 86 of them. The study results indicate that 58% to 65% of historic steelhead basins currently support O. mykiss. The pattern of basin level extirpation showed a latitudinal gradient, with the highest extirpation rate in the south, confirming that a contraction has taken place. Most of the extirpations (68%) were associated with anthropogenic barriers to fish migration (dams, flood control structures, culverts, etc.). The results suggest that the range contraction is primarily an effect of lost migration opportunities arising from the urban/rural infrastructure; however climate and other stressors may play a subsidiary role.