ANNUAL RUN-SIZE, HARVEST AND SPAWNER ESCAPEMENT ESTIMATES FOR TRINITY RIVER BASIN CHINOOK AND COHO SALMON AND STEELHEAD (Continued)
Trapping Locations and Periods
Trapping and tagging operations were conducted by TRP personnel from May through December 1990 at the same temporary weir sites near the towns of Willow Creek and Junction City in the mainstem Trinity River that were used in 1989 (Heubach et al. 1992). The downstream site, Willow Creek Weir (WCW), was located 6.7 km upstream of the town of Willow Creek, 46.8 km upstream of the Trinity River's confluence with the Klamath River, and 131.9 km downstream from Trinity River Hatchery (TRH). The upstream site, Junction City Weir (JCW) was located 6.4 km upstream of the town of Junction City, 133.2 km upstream from the Klamath River confluence, and 45.5 km downstream of TRH (Figure 1).
The WCW is used to obtain run-size and angler harvest estimates of fall chinook and coho, and steelhead in the Trinity River basin as far downstream as possible. The JCW is used to obtain run-size and angler harvest estimates of spring chinook as far downstream as is feasible during periods of high spring flows. We continue to operate the JCW through December to obtain run-size estimates of fall chinook and coho salmon and steelhead in the upper Trinity River basin.
We trapped at the JCW from 21 May through 13 December 1990, except from 28 May through 6 June when high flows prevented operation. We trapped at WCW from 24 August through 13 December 1990.
At both sites, we attempted to trap two-to-six nights per week, mid-afternoon on Monday through Friday or Sunday morning. We trapped and tagged fish only at water temperatures <21o C to avoid severely stressing the fish.
Weir and Trap Design
As in the 1989-90 season, we used the Bertoni (Alaskan) weir design at both weir sites (Figure 2). The weir was supported by wooden tripods set 2.5 m apart. The weir panels were composed of 2.4-m X 2.54-cm (8-ft. X 1-in.) electrical conduit with the centers spaced 5.4 cm apart. The conduit was supported by three pieces of aluminum channel arranged 0.92 m apart, that connected to the supporting tripods. We anchored the tripods with 1.8-m stakes driven into the stream bottom. The weir conduits were angled, with the top of the weir standing 1.8 m above the river bottom (Figure 2).
The weir guided fish toward a fyke leading to a trap which measured 2.4 m square and 1.2 m high and was covered with wood panels to prevent the fish from jumping out of the trap. The trap sides and fyke leading into the trap consisted of 2.54-cm (1.0-in.) electrical conduit welded into panels. The conduit centers were spaced 5.4 cm apart, the same space as the weir panels. The trap entrance was created by elevating the weir conduit allowing fish to enter the fyke and trap.
Processing of Fish
At both weirs, we identified all trapped salmonids to species, measured them to the nearest cm of fork length (FL), and examined them for hook and gill-net scars, hatchery marks (fin clips) and tags. All untagged salmonids judged not to be moribund and not to have spawned were tagged with a serially numbered FT-4 spaghetti tag (Project-tagged). To determine angler harvest rates, 55% (606/1,109) of the taggable spring chinook salmon at JCW received a $10-reward version of the spaghetti tags, and 54% (265/487) of the fall chinook, 65% (169/261) of coho, and 65% (174/269) of the steelhead tagged at WCW received $10- or $20-reward tags. All remaining fish received non-reward tags. All tags (both reward and non-reward) applied at Willow Creek were brown, while all tags applied at Junction City were blue.
This year we began a three-year experiment to determine the relative return rates, by anglers, of the non-reward and the $10- and $20-reward tags. We attempted to tag equal, one-third proportions of the fall chinook, coho and steelhead at WCW with each of the three spaghetti tag types (non-reward, $10-, and $20-reward tags). However, the $20 reward tags arrived after the trapping season began and, therefore, only 16% of the fall chinook received $20 reward tags. Our objective was to recover a sufficient number of tags to statistically compare the return rates of the three tag denominations.
To determine tag shedding rates, we removed one-half of the left ventral fin from all spring chinook tagged at JCW. We gave all fall chinook and coho tagged at WCW a single 6.4 mm (0.25 in.) diameter puncture on the left operculum, while those tagged at JCW received two such punctures of the left operculum. The tagged steelhead did not receive a secondary mark at either weir. We released all fish at the respective capture sites immediately after processing.
Separation of Spring- and Fall-run Chinook Salmon at the Weirs
Each year there is a temporal overlap in the annual spring and fall chinook runs in the Trinity River. Since the timing of each run varies between years, we assign a specific date each season separating the two runs so that numbers of spring and fall chinook can be determined for the run-size and angler harvest estimates. In 1990, we selected the date separating the runs based on changes in the ratio of hatchery-marked (adipose fin-clipped and coded-wire tagged [Ad+CWT]) spring to fall chinook which were spaghetti tagged at the weirs, and later recovered dead during upriver salmon spawner surveys or at TRH. Only double-tagged fish (Project-applied spaghetti tag and hatchery-applied coded-wire tag) were used for this evaluation. The race of these fish and the specific date that they were caught at the weirs could be identified because they were both coded-wire tagged (CWT) and Project-tagged fish, respectively. We also used the fish's coloration as a subjective indicator of the length of time it had been in the river. During the transition period of the run from spring to fall chinook, dark-colored fish were considered to be migrating spring chinook while light-colored fish were considered to be recently migrating fall chinook. We determined that the spring run was over at both weirs when light-colored fish clearly outnumbered dark-colored fish and carcass recoveries of double-tagged fish (Project-tagged and CWT) indicated that fall chinook dominated the run.
Separation of Spring- and Fall-run Chinook Salmon at Trinity River Hatchery
As at the weirs, there is an overlap in the migration of spring and fall chinook into TRH. To estimate the respective numbers of spring and fall chinook entering TRH, we expanded the numbers of coded-wire tags recovered from each returning coded-wire tag group by the ratio of CWT to untagged chinook salmon that occurred when they were originally released (same strain, brood year, release site and date). For example, 101,030 CWT spring chinook of code group 6-61-46, plus 385,018 unmarked spring chinook were released directly from TRH in September 1987. Since there were 3.8 unmarked chinook salmon released for every CWT chinook salmon released (385,018 unmarked/ 101,030 marked = 3.8), we multiplied the total number of CWT chinook salmon of code group 6-61-46 by 3.8 to estimate the number of unmarked fish of that release group that returned to TRH. In doing so, we assumed that return rates to TRH of both CWT and unmarked salmon were the same.
If more chinook salmon entered the hatchery on a particular sorting day than could be accounted for by the expansion of all of the coded-wire tag groups, we assumed the additional fish were naturally produced. We designated these fish spring- or fall-run fish in the same proportions that were determined by the expansion of the coded-wire tag groups.
Separation of Adult and Grilse Salmon
We designated the size separating an adult fish from a grilse for spring and fall chinook based on length frequency data obtained at the two trapping sites and at TRH, evaluated against length data obtained from groups of CWT fish that entered TRH whose exact age was known. Daily chinook salmon FL data from TRH were assigned to either spring or fall chinook when the coded-wire tag extrapolations indicated >90% of the chinook salmon entering TRH were either spring-run or fall-run fish. Daily FL data from TRH were not used when coded-wire tag extrapolations indicated the chinook salmon entering TRH were <90% of a specific run.
The length data collected at the weirs and TRH were smoothed with a moving average of five, 1-cm FL increments to determine the nadir separating grilse and adults. In the 1990-91 season, only one coho grilse was trapped at the weirs, so we based the coho grilse:adult separation on length frequency data taken from coho entering TRH.
Adult Steelhead
All steelhead >41 cm FL were adults, and steelhead <41 cm were considered half-pounders.
River Surveys
River surveys for dead, tagged fish were not conducted in the 1990-91 season, because only one dead tagged fish was recovered during the river surveys in the 1989-90 season. We continued to recover dead, tagged fish at the weirs. We examined dead salmonids for tags, fin clips, and spawning condition, and measured them to the nearest cm FL. Heads of adipose fin-clipped (hatchery-marked) fish were removed for the recovery of the coded-wire tag. After examination, the carcasses were cut in half to prevent recounting.
Tagging Mortalities
We defined all tagged salmonids recovered dead at the weir or reported by citizens as tagging mortalities, if there was no evidence they had spawned and they were recovered dead <30 days (d) after tagging. Tagged fish recovered dead >30 d after tagging or those that had spawned, regardless of the number days after tagging, were not considered tagging mortalities.
Angler Tag Returns
We processed Project tags returned by anglers to assess sport harvest rates. If not provided with the original tag return, we requested anglers to provide the date and location of their catch in a follow-up thank-you letter. The letter informed them of the fish's tagging date and location.
Salmon Spawner Surveys
The Trinity River Fisheries Investigation Project (TFIP), another element of CDFG's Klamath-Trinity Program, conducted salmon spawner (carcass) surveys in the mainstem Trinity River and its spawning tributaries from Lewiston Dam to the confluence of, and including the North Fork Trinity River, from 17 September through 20 December 1990 (Figure 1). Staff of the TFIP routinely provided us records of the species, tag number, date, and recovery location of Project-tagged fish.
Trinity River Hatchery
The TRH fish ladder was opened from 1 September 1990 through 27 March 1991. Hatchery personnel conducted fish sorting and spawning operations two-to-four days per week, depending on the numbers of fish entering TRH per day. We considered the initial day a fish was observed during sorting as the day it entered the hatchery.
On all sorting days, salmon and steelhead entering TRH were identified to species, sexed, and examined for tags, fin clips, and the secondary tagging mark. We measured all salmon and steelhead to the nearest cm FL, except those that were Project-tagged fish from the weirs. Project-tagged salmon and steelhead recovered at TRH were assigned the original FL recorded for them at the weir where they were originally tagged.
We removed Project tags from unmarked (no Ad+CWT) salmon on the initial sorting day while Project tags were removed from hatchery-marked (Ad+CWT) salmon the day they were spawned. Salmon with a secondary tagging mark and no tag were measured to the nearest cm FL and sexed. At the end of the season, we assigned these secondary marked salmon which had shed their tag, a tag number from a fish of the same species, FL, sex, and weir location where they were originally tagged and released. Tag numbers of the recovered Project-tagged steelhead were read the initial day the steelhead was sorted but the tag was not removed. On each sorting day, we gave a distinguishing fin clip to hatchery marked salmon that were placed in ponds to ripen, so the day it initially entered the hatchery could be determined when it was spawned.
On the day they were spawned, we removed the heads of all hatchery-marked (Ad+CWT) salmon and placed them in zip-lock bags with serially numbered tabs noting the date and location of recovery, species, sex, and FL. Salmon heads were given to the CDFG's Ocean Salmon Project for tag recovery and decoding. The Ocean Salmon Project provided us with a computer file of the coded-wire tags recovered for editing and analysis.
Effectively Tagged Fish
We estimated the number of 'effectively-tagged' fish by subtracting tagging mortalities of unspawned fish recovered at the weir, dead, tagged fish reported by anglers, and tagged fish recovered or reported downstream of the tagging site from the total numbers of each species tagged at the respective tagging sites.
Run-size Estimates
We determined the run-size estimates for salmon migrating into the Trinity River basin above WCW and JCW in 1990-91 by using Chapman's version of the Petersen Single Census Method (Ricker 1975):
N = (M+1) (C+1) , where
(R+1)
N = estimated run size, M = the number of 'effectively-tagged'
fish, C = the number of fish examined at TRH, and R = the number of tags recovered (including fish with a secondary tagging mark and no tag) in the hatchery sample.
We attempted to effectively tag and recover enough tagged fish to obtain 95% confidence limits of +10% of the run-size estimate. Confidence limits were determined according to the criteria established by Chapman (1948). In this analysis, the type of confidence interval estimate used is based on the number of tags recovered and the ratio of tagged to untagged fish in the recovery sample.
Each year, we examine the grilse and adult composition of the effectively tagged salmon, the sample of Project-tagged salmon recovered at TRH, and the untagged sample of salmon at TRH to determine if the run-size estimate should be stratified by grilse and adults. Run-size estimates are stratified by grilse and adult salmon when: 1) the proportions of grilse and adult salmon in the effectively tagged sample, the Project-tagged sample of salmon recovered at TRH, and the untagged sample of salmon at TRH are significantly different, statistically; and 2) there are sufficient grilse and adult salmon recovered in the tagged sample at TRH to obtain 95% confidence limits of +10% of each of the stratified portions of the run-size estimate.
If we do not stratify the salmon run-size estimate by grilse and adults, we use the proportions of grilse and adult salmon trapped at the respective weirs to estimate the numbers of grilse and adults comprising the run.
All steelhead run-size estimates are for adults only.
For the run-size estimate, we assumed 1) fish trapped and released from the weir were a random sample representative of the population; 2) tagged and untagged fish were equally vulnerable to recapture (entering TRH); 3) all Project tags and secondary tagging marks were recognized upon recovery; 4) tagged and untagged fish were randomly mixed throughout the population and among the fish recovered at TRH; and 5) we accounted for all tagging mortalities.
Angler Harvest Rates
Only $10 and $20 reward tags returned by anglers were used to determine angler harvest rates. The angler harvest rate estimate was computed as the number of reward tags returned by anglers divided by the number of effectively reward-tagged fish released.
The assumptions for the numbers of effectively reward- and non-reward-tagged fish released are the same as those for determining the run-size estimate (See "Run-size Estimates", page ). In addition, the numbers of effectively reward-tagged fish released was corrected for tag shedding by multiplying the aforementioned total by the percentage of tagged fish recovered at TRH that had not shed their tag.
The confidence limits surrounding the point harvest rate estimate were determined by tables for the binomial distribution. We attempted to effectively reward tag enough fish to obtain 95% confidence limits of <+10.0% of the harvest rate.
Angler Harvest Estimates
We estimated the numbers of fall chinook, coho, and steelhead upstream of WCW, and spring chinook upstream of JCW harvested by anglers by multiplying the run-size estimate above the respective weir site by the harvest rate estimate.
The absolute numbers of fall chinook, coho, and steelhead harvested by anglers in the Trinity River upstream of JCW was determined by multiplying the respective percentage of WCW-tagged fish reported caught upstream of the JCW by the total angler harvest estimate upstream of WCW.
Other Analyses
The mean FLs of samples were compared statistically using a Student's t-test. We analyzed the percentages or ratios of adults and grilse, marked and unmarked fish, and the angler return of non-reward and reward tags in samples by Chi-square. A continuity correction (Yates correction) was used for contingency tables of one degree of freedom (Dixon and Massey, 1969).
Weekly sampling data collected by the Project at the weirs are presented in Julian week (JW) format. Each JW is defined as one of a consecutive set of 52, weekly periods, beginning 1 January, regardless of the day of the week on which 1 January falls. The extra day in leap years is added to the ninth week, and the last day of the year is included in the 52nd week (Appendix 1). This procedure allows inter-annual comparisons of identical weekly periods.
