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2007 GR Report Summary
ADULT AND JUVENILE STEELHEAD POPULATION
SURVEYS,
GUALALA RIVER, CALIFORNIA, 2007
Richard W. DeHaven
December 31, 2007
SUMMARY: Seasonal steelhead spawning surveys (counts of adults and redds) conducted in 2002-2006 along an 18.7-mile reach (Index Reach) of the Wheatfield Fork, Gualala River, California, were continued in 2007. The Index Reach was surveyed 9.5 times (176 miles) during the 5-month spawning season from a small, aluminum drift-boat. A total of 762 adult steelhead, the highest number to date, and 38 redds, were recorded; numbers of adult fish peaked in March when 532 (70%) were recorded. Based on area-under-the-curve-trapezoidal (AUC-T) methods, 2007 survey results and 5 preceding years of count data provided the first provisional population estimates, suggesting a spawning population on the Wheatfield Fork varying up to five-fold annually, from a few hundred to about 2,500 fish, with an average annual return of about 1,200-1,700 fish. These provisional estimates are subject to revision, as estimates of survey life (SL) and observer efficiency (OE) used in the AUC-T methodology are improved and validated during future work. Provisional population estimates were more closely associated with peak annual counts than with either mean annual or expanded (using OE) mean annual counts. Summertime snorkeling surveys of JSH were also continued in 2007 at 15 established sites. Snorkeling results suggested that: (1) summertime 2007 conditions for JSH rearing and production were relatively poor, owing to well below average annual and springtime rainfall; (2) Wolf Creek continued to be important to JSH rearing and production; (3) JSH undertook large-scale movements towards the estuary in mid-summer, followed later in summer with an exodus seaward, in response to summertime breaching of the estuary impoundment; (4) over summertime, JSH rearing became greatly diminished in the main stem of the Wheatfield Fork, due to low flow and elevated water temperatures. To complement standard spawning and snorkeling surveys in 2007, three related reconnaissance-level surveys were conducted via low-level helicopter flights. During two flights in mid-March, 169 adult steelhead and 6 redds were counted during survey of 83 miles of stream, with results showing that the main stem of the Wheatfield Fork (including Index Reach), lower House Creek and the lower South Fork were good candidates for a long-term spawning survey protocol based on helicopter methodology. A third and final helicopter survey along 29 miles of main-stem stream in late September suggested utility of this approach for monitoring dewatering. During 2007, dewatering, which poses a serious impediment to river restoration and salmonid population recovery, was most pervasive as usual in the vicinity of the South and Wheatfield forks confluence.
Senior Fish and Wildlife Biologist (Retired 2004); U.S. Fish and Wildlife Service (Service), Sacramento, California. Recommended Report Citation: DeHaven, R. W. 2007. Adult and juvenile steelhead population surveys, Gualala River, California, 2007. Prepared by the author (drdehave et hotmail.com), December 31, 2007, for use by agencies, groups and individuals involved in steelhead recovery efforts. 106 pp. (This report and Appendix available on the author’s website at http://www.gualalariversteelhead.info by mid-2008.)
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