Annual Run-size, Harvest and Spawner Escapement Estimates for Trinity River Basin Chinook and Coho Salmon and Steelhead (continued)
We did not stratify the spring chinook run-size estimates upstream of JCW and fall chinook and coho upstream of both WCW and JCW by grilse and adults this year. We tagged and recovered too few grilse to estimate the grilse run-size within "10% at 95% confidence limits. Therefore, our non-stratified estimates used the respective proportions of grilse and adult spring chinook at JCW, and coho at WCW or JCW to define the grilse/adult composition of each run-size estimate. Since there was such a large disparity between the grilse/adult composition of fall chinook at WCW vs. JCW, we used the grilse/adult composition at TRH for the fall chinook runs upstream of both weirs. We made no attempt to stratify the adult steelhead run-size estimate by naturally vs. hatchery-produced fish because we believe that the fin-clipped, hatchery-produced steelhead released from TRH during 1989 and 1990 were not fully recruited as adult steelhead during the 1991-92 season.
We estimate 2,381 spring chinook (including those eventually harvested) migrated into the Trinity River basin upstream of JCW during the 1991-92 season (Table 18). Anglers caught an estimated 14.1% (336) of the spring run (Table 19). Thus, the spawning escapement above JCW was estimated to be 2,045 fish, including the 685 spring chinook that entered TRH (Table 19).
The 1991-92 season spring chinook salmon run-size and spawner escapement estimates are the lowest since the monitoring program began in 1978.
We estimate 9,207 fall chinook (including those eventually harvested) migrated into the Trinity River basin upstream of WCW during the 1991-92 season, and 7,231 of these fish continued their migration upstream of JCW (Table 18). Anglers harvested an estimated 13.8% (1,271) of the fall chinook passing WCW, including 118 fish caught upstream of JCW (Table 19). Therefore, we estimate 7,936 fall chinook spawned in the Trinity River basin upstream of WCW, and 7,113 of those fish spawned in the Trinity upstream of JCW, including 2,687 fall chinook that entered TRH (Table 19).
The 1991-92 fall chinook run-size estimate upstream of WCW was 785 fish less than in the 1990-91 season, which was the previous low since 1977, when the monitoring program began.
We estimate 9,124 coho (including those eventually harvested) migrated into the Trinity River basin upstream of WCW during the 1991-92 season, and 3,996 of these fish continued their migration upstream of JCW (Table 18). An estimated 1.2% (109) of the coho were harvested by anglers upstream of WCW, 24 of which were caught up-stream of JCW (Table 19). Thus, the spawning escapement estimate for coho upstream of WCW was 9,015 fish, including 3,972 fish that spawned upstream of JCW, 2,688 of which entered TRH.
The 1991-92 coho run size upstream of WCW is nearly 2.5 times that of the 1990-91 season, but only about one-half the size of the 1989-90 season run (Heubach et al. 1992a, 1992b).
We estimate 11,417 adult fall-run steelhead migrated upstream of WCW (including those harvested by anglers); 2,285 steelhead continued their migration upstream of JCW (Table 18). Anglers harvested an estimated 20.5% (2,340) of the steelhead upstream of WCW, 484 of which were caught upstream of JCW. Thus, we estimate the spawning escapements of adult fall-run steelhead at 9,077 and 1,801 fish upstream of WCW and JCW, respectively, 446 which entered TRH (Tables 18, 19).
1. Tag and recapture operations for adult spring-run and fall-run chinook and coho salmon, and adult fall-run steelhead being conducted in the Trinity River basin should be continued during the 1992-93 migration season, using the capture sites near Willow Creek and Junction City.
2. The use of $20-reward tags should be discontinued because of evidence that it encouraged anglers to fish exclusively for a reward-tagged fish and to recover dead salmon during the spawning season. Use of the $10-reward tags should be continued at both weir sites.
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APPENDIX 1. List of Julian weeks and their calendar date equivalents.
