The rivers of California’s Central Valley are home to one of the southernmost populations of Oncorhynchus mykiss, a versatile species whose populations can consist of a mix of river-resident rainbow trout and steelhead that migrate to the ocean. Stark declines in migratory individuals led to the listing of Central Valley steelhead as Threatened under the Endangered Species Act in 1998.
However, a major problem stands in the way of effective species recovery: a lack of data necessary to understand the population. Current knowledge of O. mykiss suggests that populations need both residents and migrants to be resilient, yet existing data on both life-history forms in the Central Valley are insufficient to assess the status and trends of either. Targeted monitoring programs that consider the unique ecology of the species are urgently needed to fill this long-standing knowledge gap.
Fortunately, O. mykiss are quite possibly the most studied fish species in the world, and a new scientific paper by FISHBIO researchers published in the current issue of San Francisco Estuary and Watershed Science proposes leveraging this knowledge to develop O. mykiss-focused monitoring that can help study the interaction between resident rainbow trout and steelhead, and can evaluate the impacts of recovery actions (Eschenroeder et al. 2022).