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ANNUAL REPORT

TRINITY RIVER BASIN SALMON AND STEELHEAD MONITORING PROJECT

1989-1990 SEASON

CHAPTER IV - JOB IV

RUN-SIZE, ANGLER HARVEST, AND SPAWNER ESCAPEMENT OF CHINOOK AND COHO SALMON IN THE TRINITY RIVER BASIN

by

Bill Heubach, Michael Lau, and Morgan Boucke

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ABSTRACT

The California Department of Fish and Game's Trinity River Project conducted tagging and recapture operations from June 1989 through April 1990 to obtain chinook and coho salmon run-size, in-river harvest, and spawning escapement estimates in the Trinity River basin. We placed weirs in the Trinity River near the towns of Junction City and Willow Creek, and trapped 1,575 spring-run and 1,933 fall-run chinook salmon (Oncorhynchus tshawytscha), and 1,131 coho salmon (O. kisutch).

Based on tagged fish recovered at Trinity River Hatchery and on the return of reward tags by anglers, we estimate 26,306 spring chinook salmon migrated into the Trinity River basin upstream of Junction City Weir and that 2,630 (10.0%) were caught by anglers, leaving 23,676 fish as potential spawners. We estimate 46,622 fall-run chinook salmon migrated past Willow Creek Weir and that 29,716 of these fish continued up the Trinity River past Junction City Weir. Anglers harvested an estimated 3,263 (7.0%) of the fall-run chinook salmon that passed Willow Creek Weir, leaving 43,359 fish as potential spawners.

The coho salmon run in the Trinity River basin upstream of Willow Creek Weir was 18,752 fish of which 12,625 continued their migration past Junction City Weir. Anglers harvested an estimated 300 (1.6%) of the coho salmon that migrated by Willow Creek Weir, leaving 18,452 fish as potential spawners.

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JOB OBJECTIVES

1. To determine the size, composition, distribution and timing of adult chinook and coho salmon runs in the Trinity River basin.

2. To determine the angler harvest and spawning escapement of Trinity River chinook and coho salmon.

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INTRODUCTION

The California Department of Fish and Game's (CDFG) Trinity River Project (TRP) conducts annual tagging and recapture operations for adult chinook and coho salmon in the main-stem Trinity River. This effort determined the composition (species, race, & proportion of marked or tagged fish), distribution, and timing of the chinook and coho salmon runs in the Trinity River basin. Recaptures of hatchery-marked or project-tagged fish are used to develop run- size, angler harvest, and spawner escapement estimates for each chinook and coho salmon run.

This is a continuation of studies that began in 1977 with the trapping, tagging, and recapture of fall-run chinook (fall chinook) and coho salmon (coho) in the Trinity River in order to determine run-size and angler harvest rates. In 1978, similar studies were added to include spring-run chinook salmon (spring chinook).

The earlier studies were funded by the U.S. Bureau of Reclamation (USBR) and Anadromous Fish Act funds administered by the National Marine Fisheries Service. Funding for the present program was through the Anadromous Fish Act monies from 1 July through 30 September 1989 and the USBR (PL 98-541) from 1 October 1989 through 30 June 1990.

Prior to the current program, all efforts to measure salmon and steelhead populations in the Trinity River basin had been restricted to various portions of the upper main stem Trinity River and certain of its tributaries, and/or the South Fork Trinity River and some of its tributaries (Gibbs 1956; La Faunce 1965a, 1965b, 1967; Miller 1975; Moffett and Smith 1950; Rogers 1970, 1972, 1973a, 1973b, 1982; Smith 1975; Weber 1965). These earlier efforts did not include fish which use the main stem and tributaries of the lower Trinity River or attempt to determine the proportion of hatchery fish in the runs and the rates at which various runs contribute to the fisheries. To develop a comprehensive management plan for the Trinity River basin, all salmon runs utilizing the basin must be considered.

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METHODS

Trapping and Tagging

Trapping Locations and Periods

Trapping and tagging operations were conducted by TRP personnel at two temporary weirs in the main stem Trinity River. 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 132.0 km downstream from Trinity River Hatchery (TRH) (Figure 1). The upstream site, Junction City Weir (JCW), was located 6.4 km upstream of the town of Junction City, 136.4 km upstream from the Klamath River confluence, and 42.4 km downstream of TRH (Figure 1).

The WCW is used to obtain run-size and angler harvest estimates of fall chinook and coho 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 relatively high spring flows. We continued to operate the JCW through December to obtain run-size estimates of fall chinook and coho in the upper Trinity River basin.

We trapped at the JCW from 4 June through 20 December 1989, except from 3 through 9 September and 23 October through 5 November when high flows or flow-induced weir damage prevented operation. We trapped at the WCW from 22 August through 20 October 1989 when storms caused high flows which severely damaged the weir and forced its removal for the season.

At both sites, we attempted to fish four nights per week, from approximately mid-afternoon on Monday through noon on Friday. We trapped and tagged fish only at water temperatures <21 oC to avoid severely stressing the fish.

Weir and Trap Design

We used the Bertoni (Alaskan) weir design at both weir sites (Figure 2). The weir was supported by wooden tripods set 2.4 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).

(Figure 1) (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 or to have spawned were tagged with a serially numbered FT-4 spaghetti tag (Project-tagged). To determine angler harvest rates, 33% of the taggable spring chinook from JCW, and 22% of the taggable fall chinook and 27% of the taggable coho from WCW were systematically tagged with a $10-reward version of the spaghetti tag. Remaining fish received a non-reward version of the spaghetti tag. All spaghetti tags (both reward and non-reward) applied at WCW were brown, whereas all those applied at JCW were blue.

To determine tag shedding rates, we removed one-half of the left ventral fin from approximately every third spring chinook tagged at JCW. We gave all fall chinook and coho tagged at WCW a single 6.4-mm (0.25-in) puncture through the opercle bone of the left operculum, while those tagged at JCW received two punctures in the same area. We released all fish at their 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 salmon runs in the Trinity River. Since the timing of each run varies among 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 1989, we selected the date separating the runs based on changes in the ratio of spring to fall chinook of hatchery origin which were spaghetti tagged at the weirs, and later recovered dead during the salmon spawner survey or at TRH. Only doubly 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 late-migrating spring chinook, while bright colored fish were considered to be recently migrating fall chinook. We determined that the spring run was over at both weirs when bright-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 tags recovered from each returning CWT 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, 100,320 fall chinook of CWT code 6-56-27, plus 735,955 unmarked fall chinook were released directly from TRH in September 1987. Since there were 7.34 unmarked chinook salmon released for every CWT chinook salmon released (735,955 unmarked/100,320 marked = 7.34), we multiplied the total number of chinook salmon of CWT group 6-56-27 by 7.34 to estimate the number of the unmarked fish of that release group that returned to TRH each day. We assumed that return rates 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 CWT groups, we assumed the additional fish were naturally produced. We designated these fish spring-run or fall-run fish in the same proportions that were determined by the expansion of the CWT groups.

Separation of Adult and Grilse Salmon

We designated the size separating an adult fish from a grilse for spring and fall chinook, and coho 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 was assigned to either spring or fall chinook when the CWT extrapolations indicated >90% of the chinook entering TRH were either spring-run or fall-run fish. Daily FL data from TRH was not used when CWT 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 1989-90 season, no coho grilse were trapped at either weir so we based the coho grilse vs. adult separation on length frequency data from those fish entering TRH.

Recovery of Tagged Fish

River Surveys

As part of the JCW operations, we surveyed the river by raft each week from June through August to recover dead salmonids. We surveyed a 12.1 km stretch from the Douglas City Camp at river km 148.5 downstream to the weir at river km 136.4. We examined dead salmonids for tags, fin clips, sex, spawning condition, and measured them to the nearest cm FL. Heads of adipose fin-clipped (hatchery-marked) fish were removed for recovery of the CWT. After examination, the carcasses were cut in half to prevent recounting. We did not survey the river between WCW and JCW in 1989, because we saw few dead fish at WCW. All tagged and untagged salmonids recovered dead at both weirs were examined and processed similarly to those on the river survey.

Tagging Mortalities

We defined all tagged salmonids recovered dead within 30 days (d) after tagging, which had not spawned, as tagging mortalities. Tagged fish that had spawned, regardless of the number of days after tagging they were recovered, and those recovered dead >30 d after tagging were not considered tagging mortalities.

Angler Tag Returns

We used 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 Fisheries Investigations Project (TFIP), another element of the CDFG's Klamath-Trinity Program, conducted salmon spawner surveys in the main stem Trinity River and its spawning tributaries from Lewiston to the confluence of, and including the North Fork Trinity River, from 18 September 1989 to 14 January 1990 (Figure 1). TFIP personnel 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 8 September 1989 through 17 March 1990. Hatchery personnel conducted fish sorting and spawning operations two to three days per week depending on the numbers of fish entering per day. We considered the initial day a fish was observed during sorting as the day it entered the hatchery.

On sorting days, salmon entering TRH were identified to species, sexed, and examined for tags, fin clips, and the secondary tagging mark. We measured all marked salmon to the nearest cm FL, except those that were Project-tagged fish from the weirs. We took FL measurements on 38% and 93% of randomly selected, unmarked chinook and coho salmon, respectively. Project-tagged salmon recovered at TRH were assigned the original FL recorded for them at the weir where they were originally tagged. Salmon with a secondary tagging mark but no tag were measured to the nearest cm FL and sexed. At the end of the season, we assigned these secondarily marked salmon which had shed their tags, a tag number from a fish of the same species, FL, and sex that had been captured at the same weir where they were originally tagged.

We removed the heads of 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 CWTs recovered for editing and analysis.

Statistical Analyses

Effectively Tagged Fish

We estimated the numbers of 'effectively tagged' fish by subtracting tagging mortalities of unspawned fish recovered at the weirs and in the river surveys, 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 1989-90 by using Chapman's version of the Petersen Single Census Method (Ricker 1975):

N = (M+1) (C+1) /(R+1), where

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.

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 recovered all tagging mortalities.

Angler Harvest Rates

Only the $10 reward tags returned by anglers were used to determine angler harvest rates. The angler harvest rate estimate was 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-tagged fish released was the same as those for determining the run-size estimate (See Run-size Estimates, above). In addition, the number of effectively reward-tagged fish released was corrected for tag shedding by multiplying that total by the percentage of tagged fish recovered at TRH that had not shed tags.

The confidence limits surrounding the point harvest rate estimate was determined by tables for the binomial distribution. We attempted to effectively reward tag enough fish to obtain 95% confidence limits of < +5.0% of the angler harvest estimate.

Angler Harvest Estimates

We estimated the numbers of spring chinook upstream of JCW, and fall chinook and coho upstream of WCW 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 and coho harvested by anglers in the Trinity River upstream of JCW were determined by multiplying the percentages of all Project-tagged fish that were reported as being caught upstream of the JCW by the total angler harvest estimates 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, and marked and unmarked fish (etc.) in samples by Chi-square. A continuity correction (Yates correction) was used for contingency tables of one degree of freedom (Dixon and Massey 1969).

Use of Standard Julian Week

Weekly sampling data collected by Project personnel at the weirs are presented in 'Julian Week' (JW) format. Each JW is defined as one of a consecutive set of 52 7-day periods, beginning 1 January, regardless of the day of the week on which 1 January falls. The extra day in leap years is lumped into the 9th week and the last day of the year into the 52nd week. This procedure allows interannual comparisons of similar 7-day periods (Appendix 1).

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