The California Department of Fish and Game, Trinity Fisheries Investigations Project is conducting a study of spring-run chinook salmon (Oncorhynchus tshawytscha) in the South Fork Trinity River basin. During the 1992-1993 season, we trapped and tagged returning adults, operated recovery weirs, conducted creel, snorkel, redd, and carcass recovery surveys, analyzed adult scales, and trapped emigrant juvenile salmon.
During adult trapping operations in the spring and summer of 1992, we captured 49 spring-run chinook salmon (spring chinook). Subsequently, 21 spring chinook were captured at recovery weirs, six of which had been marked at the tagging weir. During summer snorkel surveys throughout the basin, we observed 166 spring chinook, seventeen of which had been marked at the tagging weir. Based on the above recovery numbers we estimated the run-size to be 324 fish (266 adults and 58 grilse). Weir operation and snorkel surveys showed that the spring chinook run began this season in late April to early May, reached a peak in mid- to late-May, and declined through July and August.
From scale analysis, we determined that the age class distribution of returning fish was 22% two-year-olds, 40% three-year-olds, 32% four-year-olds, and 6% five-year-olds.
Pools were the primary adult summer holding habitat in the basin. Fourteen pools were located which held three or more spring chinook.
Based on tag returns and creel surveys, the angler harvest in the South Fork Trinity River basin was zero.
Spring chinook spawning began on 1 October and ended 26 October, 1992. During redd surveys we located 49 spring chinook redds. Redds were distributed upstream and downstream of Forest Glen in the South Fork Trinity River, with many downstream of Hyampom. Ten spring chinook carcasses were recovered, but only one was tagged.
By trapping emigrant juveniles, we found that spring chinook young-of-the-year emigration began in April, peaked in May, and was essentially complete by 1 July, 1993. No yearling spring chinook were captured.
1. To determine the size, composition, distribution, and timing of the adult spring chinook salmon run in the South Fork Trinity River basin.
2. To determine the angler harvest of spring-run chinook salmon in the South Fork Trinity River basin.
3. To determine life-history patterns of spring-run chinook salmon produced in the South Fork Trinity River basin.
This study is designed to be a thorough evaluation of the life history of spring-run chinook salmon (spring chinook), Oncorhynchus tshawytscha, within the South Fork Trinity River (SFTR) basin. This is the first major study of spring chinook in this basin. The only other study was conducted in the late summer and fall of 1964 prior to the devastating flood which occurred that year (LaFaunce 1967). The California Department of Fish and Game (CDFG) and the U.S. Forest Service (USFS) have made numerous attempts to count adult spring chinook (and spring-run steelhead) in the SFTR in order to track population trends and evaluate post-flood habitat recovery. These efforts have been sporadic, short term, and made no attempt to determine complete life history (Appendix 1). Reliable, statistically-valid population estimates were not determined during any of these efforts.
The current population of spring chinook in the SFTR is, at most, a few hundred fish. Estimates of annual run size from various sources (Appendix 1) ranged from multiples of ten to about 350 fish. The population has experienced serious decline since 1964, when the run was estimated to be 11,604 (LaFaunce 1967). Up-to-date, valid population estimates and understanding of life-history patterns are crucial to any management or restoration effort for spring chinook.
This is the third year of a proposed five-year study of SFTR spring chinook by the Trinity Fisheries Investigations Project (TFIP). Since our annual reports cover the period from 1 July through 30 June, the snorkel survey, redd and carcass recovery surveys and other observations made during summer and fall of 1992 relate to those fish trapped and marked during the 1991-1992 reporting period. Also, most scales used for life-history determinations were obtained from fish trapped and released during the 1991-1992 reporting period.
