LIFE HISTORY, DISTRIBUTION, RUN SIZE AND ANGLER HARVEST OF STEELHEAD IN THE SOUTH FORK TRINITY RIVER BASIN (continued)
We studied 262 steelhead redds throughout the SFTR basin during the 1991-92 season to assess their associated habitat and substrate components, and to measure the physical and hydraulic characteristics of each individual redd. We found redds in four basic habitat types: pools, riffles, runs, and step-runs. Fifty percent of the total stream length in the basin we surveyed consisted of step-runs. Pools, riffles, and runs each comprised about 16% of the basin stream-lengths surveyed (Figure 5). Most (42.8%) of the redds we observed were located in step-runs. However, steelhead also seemed to have the preferred the pool-riffle interchange (riffle-crest) at the tail of pools for spawning, because while pools comprised only 15% of the available habitat (based on stream length), 36.7% of the redds observed were found in these riffle-crest areas of pools (Figure 6). Riffles and runs each accounted for about 10% of the redds observed.
The average redd area was 1.24 m2 (Figure 7) and the average redd depth, measured 0.15 m upstream of the redd depression, was 23.1 cm (Figure 8). Average fish-nose water velocity (Figure 9) and mean water column velocity (Figure 10) were 0.39 and 0.42 m/sec, respectively.
The composition of the substrate provides information on the stream's suitability for spawning, insect production, and instream cover (Hunter 1991). Of the steelhead redds evaluated, the dominant and subdominant substrate components in about 90% of the redds consisted of medium gravel (25-50 mm), large gravel (50-75 mm) and small cobble (75-150 mm) in various combinations (Table 1), with an average embeddedness in the 20-29% category (Table 8). Embeddedness is the extent to which the larger substrate particles, such as boulders, cobbles, or gravels, are surrounded or covered by fine sediment. Current research indicates that when the substrate becomes more than 30% to 40% embedded, there is an accompanying loss of spawning habitat (Hunter 1991). However, this measure is very subjective and a more quantitative procedure would be beneficial. Another factor which may be important to steelhead in their selection of spawning sites is the availability of cover; 85% of the redds we observed were associated with boulders, small woody debris, large woody debris, and undercut banks (Table 9). Additional study and analysis of SFTR steelhead redds is needed to determine what spawning habitat components the fish are selecting. This information, together with stream-by-stream assessment of habitat condition and spawning activity, is needed to help determine the basin's capacity to support steelhead spawning and production. This information will also help to direct and evaluate habitat restoration efforts.
Project personnel operated two Alaskan-style weirs during the season to recover post-spawning, emigrant adult steelhead. The Hayfork Creek Weir was operated for 77 days, from 28 March through 24 June 1992 (Figure 11). The Forest Glen Weir operated for 128 days, from 27 March through 3 August 1992 (Figure 12).
In addition to our two weirs, CDFG's Trinity Fisheries Investigations Project personnel operated the Gates Road Weir (weir-panel-style) downstream from our two weirs on the SFTR at RKM 31.7 for 70 days, from 28 April through 7 July 1992 (Figure 13).
We captured 251 emigrant fall- and winter-run steelhead in the three weirs: 60 in the Hayfork Creek Weir, 160 in the Forest Glen Weir, and 31 in the Gates Road Weir. Twenty of these fish had been tagged at the Sandy Bar Weir, and the remaining 231 were unmarked. Of the 251 fish trapped at the three emigrant weirs, 122 (49%) were male, 127 (51%) were female, and 2 were of unknown sex. Mean FL for males was 63.4 cm, (range: 45-77 cm), and 61.5 cm for females (range: 41-77). Mean FL for all fish was 62.3 cm (range: 41-77 cm) (Figure 14).
Eighteen immigrant spring-run steelhead were captured in the immigrant traps (which were a part of the emigrant weirs): none in the Hayfork Creek Weir, three in the Forest Glen Weir, and 15 in the Gates Road Weir (Figure 15). Five fish were male and 13 were female. Mean FL for males was 57.2 cm (range: 51-64 cm) and 58.2 cm for females (range: 49-67 cm). Mean FL for all fish was 57.9 cm (range: 49-67 cm) (Figure 16).
Of the 493 fall- and winter-run steelhead tagged, fin-clipped, and released at the Sandy Bar Weir between 5 September 1991 and 11 February 1992, only 38 were recovered: 18 in the creel surveys, 11 at the Hayfork Creek Weir, nine at the Forest Glen Weir, and none at the Gates Road Weir.
Two hundred fifty-seven unmarked steelhead were also recovered: 26 through creel surveys, 49 at the Hayfork Creek Weir, 151 at the Forest Glen Weir, 31 and at the Gates Road Weir. Based upon these numbers, an estimated 3,741 adult steelhead (95% Poisson C.I.= 2,749-5,260) escaped into the SFTR basin during the 1991-1992 season.
Although the tagging weirs were an effective method of assessing steelhead run-size and run-timing this year, they cannot always be relied on. This was the sixth dry water-year in a row, but unpredictable weather and high river flows make weir operation in the winter difficult or impossible during most normal and wet water-years. Since our weirs cannot be operated under high-flow conditions, we may not be able to monitor the entire run during normal and wet water-years; therefore, we need to determine if alternative methods are available to gather this type of information.
From 1 July 1991 through 30 June 1992, we captured 8,904 Age 0+, 114 Age 1+, and 5 Age 2+ steelhead, and 241 juvenile chinook salmon at the Hayfork Creek and SFTR juvenile out-migrant trapping sites (Figure 1, Table 10). The peak emigration at these sites of Age 0+ steelhead occurred during May and June 1992, while peak emigration of Age 0+ chinook salmon occurred during May 1992. Age 0+ steelhead were more abundant in Hayfork Creek and chinook salmon were more abundant in the SFTR (Table 10). The mean FL of Age 0+ steelhead from the 1991 brood year (BY) increased from 51 mm in July 1991 to 73 mm by December 1991.
The mean FL of weekly samples of Age 0+ steelhead from the 1992 BY increased from 30 mm during early April 1992 to 54 mm by June 1992 (Table 11). Mean FL's of weekly samples of Age 1+ steelhead ranged from 91 to 129 mm, and Age 2+ steelhead ranged from 152 to 214 mm (Table 11). Mean FL's of weekly samples of juvenile chinook salmon from the 1992 BY ranged from 56 to 76 mm (Table 11).
TABLE 10. South Fork Trinity River basin juvenile salmonid trapping summary for the 1991-92 season.
Juvenile steelhead utilization of the five basic habitat types we used for habitat typing, was evaluated in Eltapom Creek during fall 1991 (10-13 September) and spring 1992 (8-9 June). During fall 1991 we identified 70 individual habitat units consisting of: 2.9% cascades, 40.0% pools, 34.3% riffles, 11.4% runs, and 11.4% step-runs. We selected 24 of these units to sample: 1 cascade, 9 pools, 8 riffles, 3 runs, and 3 step-runs. During spring 1992 we identified 71 individual units: 2.8% cascades, 38.0% pools, 15.5% riffles, 14.1% runs and 29.6% step-runs. We selected 26 of these units to sample: 1 cascade, 10 pools, 4 riffles, 4 runs, and 7 step-runs. During spring 1992 many of the riffles observed the previous fall were reclassified as step-runs. The average depth, from all habitat units combined, increased from 23 cm in the fall to 30 cm in the spring, and average water velocity increased from 0.20 m/sec to 0.95 m/sec. The mean water and air temperatures as measured by a hand-held thermometer during the fall survey were 15.0E C and 17.3E C, respectively. During the spring mean water and air temperatures were 15.4E C and 23.7E C, respectively. During the fall 1991 survey, we estimated the standing crop of juvenile steelhead at 3,055 fish composed of: 86% Age 0+, 11% Age 1+, and 3% Age 2+ fish (Table 12). The highest densities of Age 0+ fish were observed in riffles (0.79 fish/m2) and cascades (0.62 fish/m2), followed by step-runs and pools (0.39 and 0.30 fish/m2, respectively). The highest densities of Age 1+ fish were in cascades and pools (0.10 and 0.09 fish/m2, respectively), followed by riffles and step-runs (0.06 and 0.05 fish/m2, respectively), with the lowest densities observed in runs (0.02 fish/m2). Age 2+ fish were most prominent in pools (0.04 fish/m2), but were also found in riffles, cascades, and step-runs (0.01 fish/m2 each). Age 2+ fish were not observed in runs during fall 1991.
During the spring 1992 survey we estimated the standing crop of juvenile steelhead at 4,718 fish composed of: 88% Age 0+, 11% Age 1+, and 1% Age 2+ fish (Table 13). The densities of Age 0+ fish were relatively high in all habitat types (0.56 - 0.76 fish/m2) except in cascades, where observed density was about 1/3 that of the others (0.20 fish/m2 each). Densities of Age 1+ fish were about equal in all habitat types (0.08 - 0.10 fish/m2 each), except in runs, where density was about 1/2 that of the others (0.05 fish/m2 each). Age 2+ fish were essentially only observed in pools and step-runs (0.01 fish/m2 each), but one fish was found in a run (0.002 fish/m2).
No juvenile steelhead scales were analyzed this year because of a lack of time and trained personnel.
1. Creel surveys in the SFTR basin should continue during the 1992-93 Fiscal Year (FY) to document angler use. Additional information is needed on harvest rates, especially during low-flow conditions.
2. Adult steelhead spawner surveys should begin by 15 February weather permitting. Habitat types should be quantified during these surveys to document spawning area available to steelhead.
3. Steelhead spawning habitat studies, conducted in conjunction with the spawner surveys, should be continued throughout the basin. The quantification of available habitat will help us identify preference criteria.
4. The operation of the Alaskan weirs in Hayfork Creek and in the SFTR at Forest Glen to capture emigrant, post-spawning steelhead was effective and should continue.
5. Juvenile steelhead habitat utilization studies should continue. Other seasons should also be surveyed for comparisons with results from spring and fall. Eltapom Creek is one of the streams in the basin that is in fairly good condition with respect to sediment loads. Our habitat utilization studies should be extended to other streams that are in marginal and poor condition in order to assess their impacts on juvenile rearing.
6. Steelhead life history studies through Optical Pattern Recognition System scale analysis should continue with emphasis on the juvenile freshwater phase to assess the juvenile age structure in the basin and to determine if distinctive scale circuli patterns exist. Later these should be compared to freshwater portions on adult scales to better understand the total life history patterns of steelhead within the SFTR basin.
The authors would like to thank Judith Jackson and Kathleen Godbe for their assistance in preparing the tables for this report, and the entire staff of the Natural Stocks Assessment Project working on the South Fork Trinity River for their assistance in fieldwork and data collection.
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APPENDIX 1. List of Julian weeks and their calendar date equivalents.
