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2009 GR Report Summary

ADULT AND JUVENILE STEELHEAD POPULATION
SURVEYS, GUALALA RIVER, CALIFORNIA, 2009

Richard W. DeHaven
December 31, 2009


SUMMARY: Seasonal spawning surveys of adult steelhead conducted in 2002-2008 along an 18.7-mile reach of the Wheatfield Fork, Gualala River, California (Index Reach), were continued in 2009. The Index Reach was surveyed five times (94 miles) from a small, aluminum drift-boat between late December 2008 and mid-April 2009. A relatively low count of 126 adult fish was recorded, with a peak (82) in late December; the average of 25 adult fish per survey compared to 15 (2004) to 234 (2008) per survey for the seven preceding seasons. The provisional (pending further methodology refinements) spawning population estimate for the Wheatfield Fork, based on area-under-the-curve-trapezoidal (AUC-T) methodology, was 369 fish, the lowest value in 8 years. A total of 19 steelhead redds was also recorded; most spawning occurred upstream of the Index Reach. For the first time in 8 years, neither adult lampreys nor any lamprey redds were found. One early-summer (June 28th) snorkeling survey of JSH (juvenile steelhed) at 15 sites revealed a robust JSH population likely dominated by a strong 2008 year-class from the record 2008 return of adult fish. Rainfall in the watershed in 2009, was, for a third consecutive year, well below average, with high intra-season patchiness, including record drought and low stream flows in January. Nevertheless, a “miracle” rainfall event in early May 2009 greatly improved otherwise poor summertime rearing conditions for JSH. Efforts to improve estimates of adult steelhead spawning populations using AUC-T methodology are continuing.




Senior Fish and Wildlife Biologist (Retired 2004); U.S. Fish and Wildlife Service (Service), Sacramento, California. Recommended Report Citation: DeHaven, R. W. 2009. Adult and juvenile steelhead population surveys, Gualala River, California, 2009. Prepared by the author (drdehave et hotmail.com), December 31, 2009, for use by agencies, groups and individuals involved in steelhead recovery efforts. 29 pp. (This report, with Appendix, to be available on the author's website at http://www.gualalariversteelhead.info by mid-2010.)

 

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