Coho salmon are acknowledged to be the most imperiled of the Mattole River’s three native salmonid species. The coho salmon population in the Mattole is part of the Southern Oregon/Northern California Coast (SONCC) coho salmon Evolutionarily Significant Unit (ESU), comprised of populations inhabiting coastal streams from Punta Gorda, California north to Cape Blanco, Oregon. NOAA Fisheries listed the SONCC ESU as Threatened under the Federal Endangered Species Act (ESA) in 1997 (70 FR 37160).


Adult coho in riffle. Mattole watershed, 2002. Photo credit MSG Staff.

In 2005, the California Department of Fish and Game (CDFG) also listed coho salmon from Punta Gorda north to the California-Oregon border as Threatened under the California Endangered Species Act.


Coho young-of-the-year observed in the Mattole headwaters (Thompson Creek (RM 58.4), July 2011).

Coho salmon in the Mattole River represent the southern extent of the SONCC ESU. As such, they may be more genetically differentiated from populations nearer the center of their range, and thus contribute significantly to their respective species’ total genetic diversity and evolutionary potential (Scudder 1989; Lesica and Allendorf 1995).


Out-migrating coho smolt caught in the MSG Downstream Migrant Trap (2011). Photo credit MSG Staff.

In 2014, on the basis of a modeling approach involving 58 different watershed variables, Nature Conservancy scientist Jeanette Howard and co-authors identified those watersheds most important for coho salmon survival. Further analysis showed the most promising river for successful coho supplementation in California to be the Mattole River. We, the Mattole Salmon Group, believe that is still true. In addition, genetic analysis by Carlos Garza and co-workers have found our few remaining coho to be of wild native stocks, interbred with strays from both the north and south.