LIFE HISTORY, DISTRIBUTION, RUN SIZE AND ANGLER HARVEST OF STEELHEAD IN THE SOUTH FORK TRINITY RIVER BASIN (continued)
The Sandy Bar Weir was operated from 1 October 1992 through 8 December 1992, when high flows washed out the weir. During this period we trapped 130 adult and one half-pounder steelhead. The first steelhead was caught on 2 October, but the majority of fish were captured during increased river flows following the first fall rains (Figure 3).
We applied 38 $10-reward and 72 non-reward tags to fall-run steelhead caught at the Sandy Bar Weir this season. Five of the steelhead captured at the Sandy Bar Weir were judged to be in poor condition and were measured and released without further handling. The remaining 126 fish were given 2RV fin clips. Fourteen of the steelhead captured at Sandy Bar Weir carried tags applied at the Willow Creek Weir, located in the Trinity River 48.4 km upstream from its confluence with the Klamath River, and 3.7 km downstream from its confluence with the SFTR. A total of 168 steelhead was tagged at the Willow Creek Weir (Mark Zuspan, Assoc. Fishery Biologist, CDFG, pers. commun.). Travel times for the Willow Creek Weir-tagged steelhead ranged from 1 to 32 days, and averaged 15.1 days (Appendix 2).
On 1 November 1992 we recovered a steelhead which had been tagged at the Sandy Bar Weir the previous year (26 October 1991) as a 61-cm-FL female. At recovery this fish had grown to 65 cm FL and had been at large for 372 days. When we had released the fish in 1991 it was given a one-half left-ventral fin clip, which was still distinguishable.
Mean FL of all 131 steelhead examined was 60.5 cm (Figure 4). There was no significant difference between the mean FL of male and female steelhead caught at the weir. Predator scars were the most common (38.2%) scars observed on steelhead trapped this year at the Sandy Bar Weir (Table 2). A lower proportion (2.3%) of steelhead captured this year bore gillnet scars as compared with last year (11.3%).
TABLE 2. Scars observed on steelhead captured at the Sandy Bar Weir in the South Fork Trinity River between 1 October 1992 and 8 December 1992.
|
Scar type |
Number of fish with scars |
Percent of fish with scars |
Percent of total fish captured |
|
Gill-net scars |
3 |
4.9 |
2.3 |
|
Freshwater hook scars |
2 |
3.3 |
1.5 |
|
Ocean hook scars |
0 |
0.0 |
0.0 |
|
Predator scars |
50 |
82.0 |
38.2 |
|
Scars of unknown origin |
6 |
9.8 |
4.6 |
|
Totals: |
61 |
100.0 |
FIGURE 3. Daily catch of immigrant steelhead and river levels at the Sandy Bar Weir…
FIGURE 4. Length frequency distribution of immigrant steelhead captured at the Sandy Bar Weir…
Since the Sandy Bar Weir was only operated through 8 December 1992, we were certain that the steelhead caught were fall-run fish. It is possible that the SFTR basin also sustains a winter-run stock of steelhead. During the past two seasons (1990-91 and 1991-92) low river flows allowed us to continue weir operations longer, and we caught substantial numbers of steelhead during January and February (Wilson and Collins 1992, 1994). However, at this time we are not able to distinguish between fall-run and winter-run fish. The late-caught steelhead in the 1990-91 and 1991-92 seasons might have been fall-run fish which had been holding in the Trinity River. We plan to compare scales taken from steelhead during these two periods (i.e., October-November vs. January-February) to see if this will help us differentiate these stocks. Since winter-run fish remain in the ocean for a longer period before entering the river, we might be able to detect a larger ocean-growth pattern for winter-run stocks.
Sandy Bar Weir operations originally began in 1984 to determine the size, composition, distribution, and timing of adult salmon runs in the SFTR basin. The Sandy Bar Weir at that time was operated by the CDFG's Natural Stocks Assessment Project (NSAP), Arcata Field Office. In 1988, NSAP's SFTR Steelhead Studies Project (Weaverville Field Office) also began tagging fall- and winter-run steelhead at Sandy Bar Weir to estimate their run sizes and angler harvest rates. Between 1984 and 1990, adult chinook and coho salmon were captured, tagged, and released at the Sandy Bar Weir. Salmon escapement into the basin was estimated based on the tagged to untaqged ratio obtained through carcass surveys (Jong and Mills 1993). After the 1990-91 season we stopped tagging adult salmon at the weir, although we continued to count, measure, and take scale samples from these fish (Table 3).
TABLE 3. Number of adult salmonids caught at the Sandy Bar Weir each fall season from 1984 through 1992.
|
Year |
Beginning date |
Ending date |
No. days of weir operation |
No. of chinook caught |
No. of coho caught |
No. of steelhead caught |
|
1984 |
17-Sep-84 |
02-Nov-84 |
46 |
73 |
3 |
55 |
|
1985 |
17-Sep-85 |
17-Nov-85 |
61 |
176 |
109 |
207 |
|
1986 |
11-Aug-86 |
01-Nov-86 |
102 |
264 |
12 |
387 |
|
1987 |
16-Sep-87 |
24-Nov-87 |
69 |
455 |
17 |
243 |
|
1988 |
22-Sep-88 |
13-Nov-88 |
52 |
368 |
3 |
227 |
|
1989 |
14-Sep-89 |
23-Oct-89 |
39 |
52 |
1 |
37 |
|
1990 |
13-Sep-90 |
01-Mar-91 |
169 |
223 |
61 |
176 |
|
1991 |
04-Sep-91 |
11-Feb-92 |
160 |
202 |
135 |
495 |
|
1992 |
01-Oct-92 |
08-Dec-92 |
68 |
348 |
49 |
131 |
From 1984 through 1990, escapement of fall-run chinook salmon decreased from highs of 2,649 and 1,580 fish in 1985 and 1986, respectively, to lows of 474 to 345 fish during 1987 through 1990 (Jong and Mills 1993). Escapements remained low throughout the drought years of 1987-1991. The status of fall-run chinook salmon in the SFTR basin needs to be periodically reassessed to monitor their well-being. If normal rainfall conditions continue, it will be important to determine if any recovery of this stock occurs. The NSAP is planning to conduct this work at least once during the next five years. Long-term escapement estimates are also important to assess the natural range of population fluctuations in the basin and to evaluate the effectiveness of restoration efforts.
During the 1992-93 season we caught 348 chinook salmon (158 adults >56 cm FL, and 190 grilse <56 cm FL) (Figure 5). The size separating grilse (age 2-yr) from adult (age >2-yr) salmon was based on the nadir in the length frequency distribution within the 50-60 cm range (Figure 6); the grilse-adult size separation is generally found in this size range (Bill Heubach, Assoc. Fishery Biologist, Calif. Dept. Fish Game, pers. commun.). The catch rate remained fairly consistent through mid-November, but peaked during periods of increased flow (Figure 5). Catches of chinook salmon began declining after late-November. The catch of chinook salmon consisted of 252 males (72.4%), and 96 (27.6%) females (Figure 6). The male chinook salmon catch consisted of 73.0% grilse and 27.0% adult.
FIGURE 5. Daily catch of immigrant chinook salmon and river levels at the Sandy Bar Weir…
FIGURE 6. Length frequency distribution of immigrant chinook salmon captured at the Sandy Bar Weir.
The run of coho salmon began in early-November with the onset of increased flows, and was still in progress when the weir was washed out on 8 November (Figure 7). We caught 49 coho salmon, consisting of 23 (46.9%) males and 26 (53.1%) females (Figure 8). The male coho salmon catch consisted of 47.8% grilse and 52.2% adult.
FIGURE 7. Daily catch of immigrant coho salmon and river levels at the Sandy Bar Weir…
FIGURE 8. Length frequency distribution of immigrant coho salmon captured at the Sandy Bar Weir.
