Biological Opinions - Bureau of Reclamation

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Numer of Adult Coho Salmon
30,000
25,000
20,000
15,000
10,000
5,000
0
Figure 12.7. Estimated number of wild adult coho salmon in the Rogue River basin based on Huntley Park
sampling from 1980 to 2011 (ODFW 2013).
Though population-level estimates of abundance for most independent populations are lacking,
the best available data indicate that none of the seven diversity strata appears to support a single
viable population as defined by the extinction risk criteria (Table 12.1). In fact, most of the 30
independent populations in the ESU are at high risk of extinction because they are below or
likely below their depensation threshold.
In addition, populations that are under depensation have increased likelihood of being extirpated.
Extirpations have already occurred in the Eel River basin and are likely in the interior Klamath
River basin for one or all year classes (e.g., Shasta and Scott rivers), Bear River, and Mattole
River. Coho salmon spawners in the Eel River watershed, which historically supported
significant spawners (e.g., 50,000 to 100,000 per year; Yoshiyama and Moyle 2010), have
declined. Yoshiyama and Moyle (2010) concluded that coho salmon populations in the Eel
River basin appear to be headed for extirpation by 2025. One population contains critically low
numbers (i.e., Upper Mainstem Eel River; with only a total of 7 coho salmon adults counted at
the Van Arsdale Fish Station in over six decades; Jahn 2010). Although long term spawner data
are not available, both NMFS and CDFW believe the Lower Eel/Van Duzen River, Middle
Mainstem Eel and Mainstem Eel River populations are likely below the depensation threshold,
and thus are at a high risk of extinction. The only population in the Eel River basin that is likely
to be above its depensation threshold is the South Fork Eel River, which also has significantly
declined from historical numbers (Figure 12.8).
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