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2008 GR Report Summary
ADULT AND JUVENILE STEELHEAD POPULATION
SURVEYS,
GUALALA RIVER, CALIFORNIA, 2008
Richard W. DeHaven
December 31, 2008
SUMMARY: Seasonal spawning surveys of adult steelhead conducted in 2002-2007 along an
18.7-mile reach (Index Reach) of the Wheatfield Fork, Gualala River, California, were continued
in 2008. The Index Reach was surveyed six times (112 miles) from a small, aluminum drift-boat
between late December 2007 and mid-April 2008. The highest seasonal total count of fish to
date–1,402–was recorded, with numbers peaking in late January and March; the average of 234
adult fish per survey compared to a range of 15 (2004) to 84 (2007) over the six preceding
seasons. A provisional (pending further refinements) spawning population estimate for the
Wheatfield Fork, based on area-under-the-curve-trapezoidal (AUC-T) methodology, was 4,300-5,800 fish, or about two to twelve times higher than the six earlier (high-low) seasonal estimates.
The population uptick in 2008 likely resulted from good rearing conditions (lower water
temperatures, higher stream flows, and lack of summertime dewatering) and production for
juvenile steelhead (JSH) in summer, 2005 and 2006, due to abundant springtime rainfall both
years. A total of 47 steelhead redds was also recorded, although as in past years, most spawning
occurred upstream of the Index Reach. Axillary spawning surveys in 2008 along the lower half
of the Index Reach, done to improve estimates of Survey Life (SL) integral to the AUC-T
methodology, provided a new SL function to account for how fish movements slow and
“stacking” then occurs at “favored” holding sites, as stream flow lowers from 150 to 75 cfs.
Summertime snorkeling surveys of JSH were also continued in 2008 at 15 established 100-ft-long sites. Snorkeling results in June revealed high densities of JSH (366/site=3.7/ft), a clear
reflection of a large 2008 spawning run. However, owing to record springtime drought in the
watershed, with only 1 inch (12% of average) of rainfall during March-May, poor conditions for
JSH rearing and production subsequently ensued. By late August 2008, JSH densities had
declined dramatically to levels (57/site=0.6/ft) similar to previous seasons, a likely result of
widespread dewatering, related elevated water temperatures, and lack of stream connectivity
needed for JSH to escape lethal conditions and move to cool-water refugia. Summertime
dewatering in 2008 was the most severe the author has observed on the stream in 4 decades and
this worsening phenomenon poses a serious impediment to salmonid restoration.
Senior Fish and Wildlife Biologist (Retired 2004); U.S. Fish and Wildlife Service (Service), Sacramento, California. Recommended Report Citation: DeHaven, R. W. 2008. Adult and juvenile steelhead population surveys, Gualala
River, California, 2008. Prepared by the author (drdehave et hotmail.com), December 31, 2008, for use by agencies,
groups and individuals involved in steelhead recovery efforts. 67 pp. (This report, with Appendix, to be available
on the author's website at http://www.gualalariversteelhead.info by mid-2009.)
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