Biological Opinions - Bureau of Reclamation

few local ranchers and water districts, including the MWCD, to provide a pulse flow in the
Shasta River to improve juvenile salmonid migration. These pulse flow events temporarily
restored the conservation value of the Shasta River migration corridor, and provided juvenile
coho salmon with favorable conditions to seek out ideal cold water summer habitats scattered
throughout the upper Shasta River.
11.3.4.3 Adult Migration Corridor
The current physical and hydrologic conditions of the adult migration corridor in the Shasta
River are likely properly functioning in a manner that supports the conservation role of the adult
migration corridor. Water quality is suitable for upstream adult migration, and flow volume is
above the threshold at which physical barriers are likely to form. Annually, persistent low flow
conditions through October 1st, the end of the irrigation season, can also constrain the migration
and distribution of spawning adult salmon.
11.3.4.4 Spawning Areas
The Shasta River in particular, with its cold flows and high productivity was once especially
productive for anadromous fishes. The current distribution of spawners is limited to the
mainstem Shasta River from RM 17 to RM 23, Big Springs Creek, lower Parks Creek, and the
Shasta River Canyon. The reduction of LWD recruitment, channel margin degradation, and
excessive sediment has limited the development of complex stream habitat necessary to sustain
spawning habitat in the Shasta Valley. Persistent low flow conditions through the end of the
irrigation season (October 1) can also constrain the timing and distribution of spawning adult
coho salmon.
Coho salmon spawning has been observed in the Shasta River Canyon, lower Yreka Creek,
throughout the Big Springs Complex area, and in Lower Parks Creek. Recent surveys have
shown that channel conditions in the Shasta River mainstem and one of its most important
tributary, Parks Creek, generally are poor and likely limit salmonid production. In some reaches,
particularly in the lower canyon and the reach below the Dwinnell Dam, limited recruitment of
coarse gravels is likely contributing to a decline in abundance of spawning gravels (Buer 1981).
The causes of the decline in gravels include gravel trapping by Dwinnell Dam and other
diversions, bank-stabilization efforts, and historical gravel mining in the channel. In a 1994
study of Shasta River gravel quality, Jong (1995) found that small sediment particles and fines
(