By John Bowman
Siskiyou Daily News
April 26, 2012
John Bowman The Montague Water Conservation District
last week released additional water from Dwinnell Dam to
help threatened coho migrate out of the Shasta River on
their way to the ocean.
Lake Shastina, Calif. — Coho salmon juveniles may have an easier time migrating out of the Shasta River on their way to the ocean this year. On Friday, the Shasta Valley Resource Conservation District (RCD) and the Montague Water Conservation District (MWCD) collaborated to release additional water from Lake Shastina for a 16-hour period in an attempt to aid the fish on their downstream migration.
Monitoring efforts on the Shasta River in the recent past have shown that outmigrant juvenile coho salmon – known as smolts – have sustained high mortality while migrating out of the upper Shasta River from Dwinnell Dam to the confluence of Parks Creek.
This migration difficulty is believed to be due to low flow, which has three negative effects:
• It is hard for smolts to move over obstacles such as beaver dams or logs jams when low flows have no natural way to increase when spring rains occur but are impounded by reservoirs;
• Lower flows require fish to travel through shallow water which can increase the risk of predation; and
• Shallow water heats up quickly if the daytime temperatures are high, especially early in the season when vegetation that would normally shade the water has not leafed out.
These cumulative effects mean that low flow situations can be deadly for fish whose instincts tell them to head downstream, in contrast to fish hatched this year, which will stay in the river for another year and have the option of moving upstream to cold water refuges.
On April 12, PIT tagged juvenile coho from brood year 2010 (hatched in spring of 2011) were detected and observed rearing in the upper Shasta River. After rearing in fresh water for over a year, these fish are now ready to migrate downstream to the ocean.
Studies have shown that this migration typically peaks around the new moon (this year, April 21).
Local resource managers and scientists were ready for that peak and decided to take action to assist the migration in order to minimize mortality and hopefully increase returning adults when the 2010 brood-year returns to spawn in 2013.
To achieve an increased water release, the Shasta Valley RCD worked with the MWCD and agencies to coordinate a plan to increase upper Shasta River flows by 30 cubic feet per second (cfs) in an attempt to move fish safely downstream. Once the fish reach the Nature Conservancy’s property, natural flows increase below the confluence with Parks Creek. Big Springs Creek also joins the river just downstream from Parks Creek. The combined effects of these major tributaries offer sufficient flow and cold water temperatures to see the fish safely down to the Klamath River.
The MWCD increased flows from Dwinnell Dam by 10 cfs per hour, beginning at 3 p.m. on Friday and continuing until 6 a.m. on Saturday. The release was then ramped down to the original flow by 10 cfs per hour until 8 a.m. on Saturday.
California Department of Fish and Game (CDFG) staff, in anticipation of the release, also notched beaver dams on the upper Shasta to ensure fish passage over them.
Following the release, CDFG will monitor the effects of the increased flows on habitat, juvenile fish movement and mortality.
Sensor arrays are in place to track PIT tagged fish as they move in the river and head downstream.
“We hope to show that the increased flows will lessen the mortality observed in past years,” a press release from the RCD stated. “Hotter weather is predicted on Friday and Saturday and we are monitoring to see if the additional water aids in keeping upper Shasta River water colder, thus reducing additional stress and/or the possibility of mortality due to increased water temperature.”
According to the RCD, results of the effort to track outmigrating coho will be available soon. These results will help define the effects of the flow release and gauge the success of this experimental cooperative effort to aid the annual outmigration of coho.
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