Biological Opinions - Bureau of Reclamation

nutrient loads, insufficient pH levels and other water quality factors also afflict juvenile
migration corridors.
11.2.1.3 Adult Migration Corridors
Adult migration corridors should provide satisfactory water quality, water quantity, water
temperature, water velocity, cover/shelter and safe passage conditions in order for adults to reach
spawning areas. Adults generally migrate in the fall or winter months to spawning areas. During
this time of year, suspended sediment makes respiration for adults difficult. Removal or nonrecruitment
of woody debris and stream habitat simplification limits the amount of cover and
shelter needed for adults to rest during high flow events. Low flows in streams can physically
hinder adult migration, especially if fall rain storms are late or insufficient to raise water levels
enough to ensure adequate passage. Poorly designed culverts and other road crossings have
truncated adult migration corridors and cut off hundreds of miles of stream habitat throughout
the SONCC coho salmon ESU. While adult migration corridors are a necessary step in the
lifecycle for the species, the condition of this particular essential habitat type in the ESU is
probably not as limiting, in terms of recovery of the species, as other essential habitat types, such
as juvenile summer and winter rearing areas.
11.2.1.4 Spawning Areas
Spawning areas for SONCC coho salmon must include adequate substrate, water quality, water
quantity, water temperature, and water velocity to ensure successful redd building, egg
deposition and egg to fry survival. Coho salmon spawn in smaller tributary streams from
November through January in the ESU. A widespread problem throughout the ESU is
sedimentation and embedding of spawning gravels, which makes redd building for adults
difficult and decreases egg-to-fry survival. Excessive runoff from storms, which causes redd
scouring, is another issue that plagues adult spawning areas. Low or non-recruitment of
spawning gravels is common throughout the ESU, limiting the amount of spawning habitat.
11.2.1.5 SONCC Coho Salmon ESU Critical Habitat Summary
The current function of the majority of critical habitat in the SONCC coho salmon ESU has been
degraded and fails to support functioning essential habitat features. Although there are
exceptions, the majority of streams and rivers in the ESU have impaired habitat. Additionally,
critical habitat in the ESU often lacks the ability to establish essential features due to ongoing
human activities. For example, large dams, such as William L. Jess Dam on the Rogue River in
Oregon, stop the recruitment of spawning gravels and large wood, which impacts both an
essential habitat type (spawning areas) as well as an essential feature of spawning areas
(substrate). Water use in many regions throughout the ESU reduces summer base flows, which
limits the establishment of several essential features such as water quality and water quantity.
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