Staff of the California Department of Fish and Game's, Trinity Fisheries Investigations Project conducted a mark-and-recovery, salmon spawner survey of a portion of the mid-Trinity River basin from 17 September through 20 December 1990. We surveyed the mainstem Trinity River from the upstream limit of anadromous migration at Lewiston Dam to a point 63.4 km downstream at the confluence of the North Fork Trinity River. Selected portions of its major tributaries that were accessible to anadromous fish were also surveyed. We examined 752 chinook salmon (Oncorhynchus tshawytscha) and 61 coho salmon (O. kisutch) carcasses during the survey.
Chinook and coho salmon spawned throughout the entire mainstem survey section, but spawner density was highest in the uppermost 3.2 km of river, generally decreasing in a downstream direction. Salmon spawning was negligible in the tributaries this year. We found only seven chinook and one coho salmon during the tributary surveys.
Approximately 22% of the spring-run, 5% of the fall-run chinook, and 13% of the coho salmon females died prior to spawning. While these chinook salmon prespawning mortality rates are lower than in the previous two years, they are still excessively high. Limited holding and spawning habitat in the upper mainstem is the probable cause of the high prespawning mortality.
We recovered both spring-run and fall-run chinook salmon in the survey. Spring-run chinook salmon dominated recovery until late October, thereafter fall-run fish became the predominant race. Coho salmon were first noted in the mainstem Trinity River survey during mid-October, their numbers peaked mid-November, and they were essentially gone by mid-December.
Based on the recovery of adipose fin-clipped chinook salmon, we estimate that 30.2% of the spring-run and 36.7% of the fall-run chinook spawners observed in the survey were of hatchery origin.
Fork lengths of adult spring- and fall-run chinook salmon from the mainstem Trinity River averaged 73.4 cm (range: 55-99 cm) and 72.2 cm (range: 54-91 cm), respectively. Adult chinook salmon composed 96.6% of the spring run and 87.5% of the fall run with grilse composing the remainder. Coho were not measured during the survey.
1. To determine, through a system of spawning ground surveys, the distribution of naturally spawning chinook and coho salmon in the mainstem Trinity River and its tributaries upstream of, and including the North Fork Trinity River.
2. To determine the incidence of pre-spawning mortality among naturally spawning salmon in the mainstem Trinity River and its tributaries upstream of, and including the North Fork Trinity River.
3. To determine the size, sex composition, and incidence of marked and tagged individuals among the naturally spawning populations in the mainstem Trinity River and its tributaries upstream of, and including the North Fork Trinity River.
4. To determine spawner distributions within the mainstem Trinity River upstream of the North Fork Trinity River.
This year the California Department of Fish and Game's (CDFG) Trinity Fisheries Investigations Project (TFIP) completed the twenty-third salmon spawner survey conducted in the mainstem Trinity River since 1942. The first three surveys (Moffett and Smith 1950, Gibbs 1956, and Weber 1965) were fishery evaluations prior to the construction of Lewiston Dam. The remaining nineteen (La Faunce 1965, Rogers 1970, 1973, 1982; Miller 1972, 1973, 1974, 1976, 1978, 1979, 1980, 1981, 1982, 1984, 1985; Smith 1975, Stempel 1988, and Zuspan 1991a, 1992a) were designed to evaluate the effects of the existing dam on the salmon resource.
In 1984, The Trinity River Basin Fish and Wildlife Management Program was enacted by Congress (Public Law 98-541). This law appropriated approximately $57 million to be spent for fishery and wildlife restoration, and monitoring within the Trinity River basin.
This survey, and those scheduled for following years by CDFG's TFIP, will help to evaluate the effectiveness of increasing spawning and holding habitat within the basin through habitat improvement efforts that are part of the restoration program.
Our study area included the mainstem Trinity River from its upstream limit to anadromous fish migration at Lewiston Dam (River km 180.1) to the confluence of North Fork Trinity River, 63.4 km downstream (Figure 1). Previous studies have divided the river into either a four- or seven-zone system. The seven-zone system was used in 1987 by the United States Fish and Wildlife Service (USFWS) (Stempel 1988) and again in 1989 by TFIP (Zuspan 1992a). Prior to this, with the exception of Moffett and Smith 1950, all surveys were based on a system using four zones in the river reach below Lewiston Dam (Gibbs 1956; La Faunce 1965; Rogers 1970, 1973, 1982; Miller 1972, 1973, 1974, 1976, 1978, 1979, 1980, 1981, 1982, 1984, 1985; Smith 1975; Weber 1965; Zuspan 1991a). Our 1990-1991 data were collected based on both zone systems. We will summarize data in this report based only on the seven-zone system as it allows comparisons of different river sections in finer detail. By also recording data using the four-zone system, we will be able to compare historic and current trends in subsequent reports.
FIGURE 1. Map of the Trinity River basin showing the mainstem spawner survey zones and areas of the tributaries surveyed in the 1990-91 spawner survey (seven-zone system -Stempel, 1988).
TABLE 1. Description and lengths of river zones used in the 1990-91 mainstem Trinity River spawner survey.
River kms for locations used in the 1989-90 spawner survey (Zuspan 1992a) were taken from sources including; 1) a previous spawner survey (Stempel 1988); 2) a river mile index (Pacific Southwest Inter-Agency Committee 1973), and a United States Forest Service map of Trinity National Forest. However, due to the poor resolution of the map and inconsistencies in the referenced reports, minor errors in river location were made in the 1989-90 report. Therefore, for this report and those in future years, all river location references will be taken from a series of 7.5-minute, United States Geological Survey topographic maps (Appendix 1).
TFIP staff conducted the survey using 12-ft Avon inflatable rafts equipped with rowing frames. Raft crews consisted of a rower, and one or two personnel to recover carcasses. To increase coverage of the highly productive upper two sections, two rafts were used simultaneously, with one covering each side of the river. Carcasses were recovered on foot along the shore or, in deep water, from the rafts with long handled gigs. We surveyed the entire mainstem Trinity River study section once a week throughout the salmon spawning season.
We determined spawning condition in female salmon by direct observation of the ovaries. Fish were classified as either spawned or unspawned based on egg retention. Females which retained over 50% of their eggs were classified as unspawned. Male spawning condition was not assessed, as its determination was considered to be too subjective.
All carcasses we observed were identified by species and examined for an adipose fin-clip (Ad-clip) indicating the presence of a coded-wire tag (CWT) in their snout. To increase our likelihood of recovering all Ad-clipped fish, we considered any fish with a missing or otherwise imperfect adipose fin to be Ad-clipped. Fish were further examined for the presence of an external tag (spaghetti tag) and an operculum punch, applied as part of an ongoing study by other elements of the CDFG's Klamath-Trinity Program. Spaghetti tags and operculum punches (Program marks) are placed on returning adult fish by CDFG staff at three trapping and tagging stations downstream of the spawner survey area, to monitor escapement and harvest of returning adult salmonids. The spaghetti-tagged salmon also receive an identifying operculum punch in order to estimate tag shedding rates of fish tagged at the three sites. The first site is located at the mouth of the Klamath River where returning fall-run chinook salmon, coho salmon, and steelhead are captured in a seine and tagged. The second site upstream is Willow Creek Weir, located at river km 32.2 on the mainstem Trinity River. The last site is Junction City Weir at river km 136.4 on the mainstem Trinity River. Spring-run and fall-run chinook salmon, coho salmon, and steelhead are trapped and tagged at both Willow Creek and Junction City weirs.
We classified all chinook salmon carcasses as either condition one or two, based on the extent of body deterioration. Condition-one fish were the freshest, having at least one clear eye and a relatively firm body. Condition-one fish were assumed to have died within one week prior to recovery. Condition-two fish were in various advanced stages of decomposition and assumed to have died more than one week prior to recovery. We did not count partially intact fish skeletons, because they could have represented Program-marked or condition-two fish which had already been counted and chopped in half during a previous week's survey.
All chinook salmon we recovered were further classified into four categories: 1) Ad-clipped fish; 2) Program-marked fish; 3) condition-one, unmarked fish; 4) condition-two, unmarked fish. The category assigned determined what data we collected from each fish.
We determined the species and condition (i.e. one or two) of Ad-clipped fish. Heads of Ad-clipped fish were removed and retained for later CWT recovery and decoding.
Program-marked fish were sexed and their spawning condition assessed. We removed any spaghetti tags and then cut the fish in half with a machete to prevent recounting in future weeks. Spaghetti tags have a unique number which allowed determination of date and location of tagging.
Condition-one fish which were neither Ad-clipped nor Program-marked were flagged and returned to moving water for subsequent recovery, and a systematically collected subsample of them were measured for FL (cm). Flags consisted of plastic survey tape wrapped tightly around a colored hog ring and affixed to the left mandible of the carcass. The survey tape was wrapped so tightly around the hog ring, that it amounted to no more than a colored coating, with less than 2.5 cm of tape extending from the hog ring at any time. Flag colors were changed weekly so that, on recovery, the week of flagging could be determined. The hog rings used to attach the flagging were color coded to indicate in which zone they were affixed, so that we could determine the incidence of carcasses drifting into another recovery zone. Chinook < 55 cm were preliminarily classified as grilse during the carcass surveys. Actual grilse to adult ratios for the whole population of chinook in this year's run were determined from post-season evaluations of length frequency and CWT data. Adult and grilse salmon analysis in this report is based on the post-season size determinations.
Condition-two fish which were neither Ad-clipped nor Program-marked were checked for the presence of a flag and, if possible, their sex and spawning condition was assessed. If a flag was present, the color of the flagging tape and the underlying ring were recorded, and all fish were then cut in half to prevent later recovery and re-counting of the same fish.
All coho salmon collected were checked for the presence of Ad-clips or Program-marks. When possible, sex and spawning condition were determined and then all coho salmon were cut in half to prevent future re-counting. Coho carcasses were not used in the flagging experiment, since they would have required a separate series of flag colors to segregate them from flagged chinook salmon.
Tributaries to the mainstem Trinity River, specifically Rush Creek, Grass Valley Creek, Indian Creek, Reading Creek, Browns Creek, Weaver Creek, Canyon Creek, East Fork of the North Fork Trinity River, and the mainstem North Fork Trinity River, were surveyed on foot once a week throughout the chinook salmon spawning season. Sections surveyed for each tributary ranged in length from 1.9 to 4.0 km, and were chosen based on accessibility and their historic use by chinook salmon spawners (Figure 1). The survey began with the onset of chinook salmon spawning in each tributary and continued until spawning ended
TABLE 2. Trinity River tributaries surveyed in the 1990-91 spawner survey.
We classified all identifiable chinook salmon recovered into the four categories used in the mainstem spawner survey and handled them accordingly (see above). However, sex and prespawning condition was assessed only for fish collected from the mainstem Trinity River. Too few fish were observed in the tributaries to compose an adequate sample and most of those observed were condition-one fish which we needed to flag for spawning escapement estimates. Coho salmon were counted and cut in half upon recovery. Chinook salmon redds, when observed for the first time, were counted and recorded.
Aerial flights and ground-truthing surveys were made of each tributary to determine the percentage of the total available spawning area within each tributary represented by each of our ongoing spawner survey zones. Flights were made during the peak of spawning activity to observe redds and locate the upstream limit of spawning. Follow-up ground-truthing surveys were made, when necessary, to make total redd counts for both the whole tributary and its spawner survey zone. The percentage of the total redds occurring in a survey zone during the aforementioned count was assumed to represent the percentage of the total spawning in each tributary that took place within the survey zone.
Mainstem Trinity River Spawner Surveys
Chinook Salmon. We examined 752 chinook salmon during the spawner survey. These included 53 Ad-clipped fish, 75 Program- marked fish (eight also Ad-clipped), 435 unmarked condition-one fish which we flagged, and 197 unmarked condition-two fish. We also recaptured and re-examined 145 fish which we had flagged in previous weeks (Appendix 2). No whole skeletons were observed.
Coho Salmon. We recovered 61 coho salmon in the spawner survey, including one Ad-clipped and one Program-marked fish (Appendix 3), and did not see any whole skeletons.
Tributary Spawner Surveys
Chinook Salmon. We found only seven chinook salmon in the nine tributaries surveyed this season. These included one Ad-clipped fish, five condition-one fish which we flagged, and one skeleton. We re-examined two chinook which we had flagged in prior weeks (Appendix 4).
Coho Salmon. One coho salmon was examined in the tributaries this season (Appendix 4), and no skeletons were observed.
Only chinook salmon recovered in the mainstem Trinity River were used to determine spring- and fall-run spawning intervals. Both spring and fall races of chinook salmon were observed in the mainstem survey. A date separating the two races was determined from CWTed and Program-marked chinook salmon. Spring-run chinook salmon dominated our recoveries through the sixth week of the survey ending 21 October 1990. Some overlap of spring- and fall-run chinook salmon occurred during the sixth week ending 28 October 1990. Fall-run chinook salmon became predominant by the seventh week of the survey which began 29 October 1990. For the purposes of this report, all chinook recovered prior to 29 October 1990 are considered spring race while those recovered from that date onward are considered fall race (Figure 2). For comparison, the dates separating spring- and fall-run chinook in previous years were 11 October in 1988 and 23 October in 1989 (Zuspan 1991a, 1992a).
FIGURE 2. Chinook salmon spawning interval determined from weekly carcass recoveries of coded-wire-tagged and Program-marked fish in the 1990-91 Trinity River spawner survey.
Spring-run Chinook Salmon
Mainstem Trinity River. We measured 236 spring-run chinook salmon to the nearest cm fork length (FL) during the survey. Adults (fish > 54 cm3/ FL [Bill Heubach, Calif. Dept. Fish and Game, pers. comm.]) composed 96.6% (228/236) of the spring-run chinook salmon observed in the spawner survey, while grilse (fish < 54 cm FL) composed the remaining 3.4% (8/236)
TABLE 3. Numbers and percentages of spring-run chinook salmon grilse observed in the spawner survey and at two fixed locations in the Trinity River basin during the 1990-91 season.
FIGURE 3. Fork length distribution, in 2-cm increments, of spring-run chinook salmon measured in the mainstem Trinity River during the 1990-91 spawner survey.
For comparison, the percentages of grilse in the spring-run chinook sampled at Junction City Weir and Trinity River Hatchery in 1990-91 were 2.9% and 4.1%, respectively. There was no significant difference in the percentage of grilse sampled the three sites (X2=0.277, df=2, p=0.871).
Tributaries. Based on the date at which we first observed spawning activity, we concluded that no spring-run chinook salmon were recovered in the tributaries this season.
Fall-run Chinook Salmon
Mainstem Trinity River. We measured (cm FL) 192 fall-run chinook salmon this season. Adults (fish > 53 cm FL [Bill Heubach, Calif. Dept. Fish and Game, pers. comm.]) composed 87.5% of the fall-run chinook salmon observed in the spawner survey, while grilse (fish <53 cm FL3/) composed the remaining 12.5%
The percentages of fall-run chinook salmon grilse at the different sampling sites ranged from 6.3% to 21.6% (Table 4), and the differences were highly significant (X2=72.9, df=3, p<0.001). The reason for the differences in proportions between the sample sites is unknown.
Tributaries. Only five chinook salmon were measured during the tributary survey this season. Four of the five (80%) were adults.
TABLE 4. Numbers and percentages of fall-run chinook salmon grilse observed in the spawner surveys and at three fixed locations in the Trinity River basin during the 1990-91 season.
FIGURE 4. Fork length distribution, in 2-cm increments, of fall-run chinook salmon measured in the mainstem Trinity River during the 1990-91 spawner survey.
Sex was determined only for fish recovered from the mainstem Trinity River that were either condition-two unmarked fish, Program-marked fish, or flagged fish recaptured in the carcass survey.
We determined the sex of 304 adult chinook salmon during the survey (152 spring-run and 152 fall-run). Of the adult spring-run chinook salmon observed, 74.3% were females, while adult fall-run fish were 67.1% females. The percentages of females in the survey were generally highest during the early and late weeks of the survey and lowest during the middle weeks (Figure 5).
FIGURE 5. Percent females in the adult chinook salmon population observed in the mainstem Trinity river during the 1990-91 spawner survey.
The preponderance of females in the adult chinook salmon run has been noted in all but two of the previous surveys and has ranged from 73.6% to 25.8% (Appendix 5). The preponderance of females among adult fish results when males return as grilse, thereby decreasing the number of males left to return as adults.
We determined the sex of 59 coho, 80% (47) of which were females. For comparison, 42.4% and 57.1% of the coho we examined in 1988 and 1989, respectively, were females (Zuspan 1991a, 1992a). Not enough coho salmon were recovered this year to evaluate seasonal trends in their sex ratio. Last year, the seasonal trend in sex ratio for coho salmon was similar to that of chinook (Zuspan 1992a).
Prespawning mortality was determined only for fish recovered in the mainstem Trinity River that were either condition-two unmarked fish, Program-marked fish, or flagged fish recaptured in the carcass survey.
We determined the spawning condition of 207 adult female chinook salmon, including 97 spring-run and 110 fall-run fish. Prespawning mortality was 22% (21/97) and 5% (6/110) for spring- and fall-run female chinook salmon, respectively. Prespawning mortality rates were generally higher early in the survey and decreased through time (Figure 6).
FIGURE 6. Adult female chinook salmon prespawning mortality observed in the mainstem Trinity River during the 1990-91 spawner survey.
The higher prespawning mortality rate for female spring-run chinook salmon is probably related to the added stress imposed by the extended time they spend in the river.
The overall prespawning mortality rate of both races of female chinook salmon was 13.0%. For comparison, overall (spring- and fall-run) prespawning mortality of female chinook salmon has ranged from 1.5% to 44.9%, averaging 12.8% during previous surveys (Appendix 6).
Forty-seven adult female coho salmon were examined for spawning condition during the survey. The prespawning mortality rate for these fish was 13% (6/47). For comparison, in 1988 and 1989, the prespawning mortality rates of adult female coho salmon were 25.6% and 6.2%, respectively (Zuspan 1991a, 1992a). Coho prespawning mortality rates were not reported in surveys prior to 1988.