SALMON SPAWNER SURVEYS IN THE UPPER TRINITY RIVER BASIN (continued)

RESULTS AND DISCUSSION

Numbers Observed

Mainstem Trinity River Spawner Surveys

Chinook Salmon. We examined 982 chinook salmon carcasses during the mainstem spawner survey. These included 11 Ad-clipped fish, 57 Program-marked fish (two of which were Ad-clipped), 456 unmarked condition-one carcasses which we flagged, and 460 unmarked condition-two carcasses. We recovered 139 carcasses which we had flagged in previous weeks (Appendix 3). No whole fish skeletons were observed.

Coho Salmon. We did not observe any coho carcasses until the eighth week of the survey. We recovered 51 adult and 2 grilse coho carcasses, including 1 Ad-clipped and 11 Program-marked carcasses (one of which was also Ad-clipped), and did not see any whole fish skeletons (Appendix 4).

Tributary Spawner Surveys

Chinook Salmon. We found only 44 chinook salmon carcasses in the ten tributaries surveyed this season. These consisted of 36 condition-one carcasses which we flagged, 3 Program-marked carcasses, and one Ad-clipped carcass. We also counted 8 fish skeletons. We recovered 14 chinook carcasses which we had flagged in prior weeks (Appendix 5).

Coho Salmon. We examined 11 coho carcasses in the tributaries this season (Appendix 5), including two which were Program-marked. No fish skeletons were observed.

Distinguishing Between Spring and Fall Chinook Salmon Runs

Since both spring and fall runs of chinook salmon (spring chinook and fall chinook) were observed in the mainstem survey, we subjectively determined a date separating the two races based on recoveries of CWTed and Program-marked chinook salmon. Spring chinook dominated our recoveries through the eighth week of the survey ending 8 November 1992. Overlap of spring and fall chinook occurred beginning the sixth week of the survey. Fall chinook became predominate by the ninth week which began 9 November 1992. For the purposes of this report, the 225 flagged chinook carcasses recovered prior to 9 November were considered spring-run, while the 231 flagged carcasses recovered from that date onward were considered fall-run (Figure 2).

For comparison, separation dates of spring and fall chinook in previous years were 11 October in 1988, 23 October in 1989, 29 October in 1990, and 28 October in 1991 (Zuspan 1991, 1992a, 1992b, 1994).

FIGURE 2. Weekly proportions of spring- and fall-run chinook salmon observed in the 1992-93 Trinity River spawner survey.

Size Composition

Spring-run Chinook Salmon

We measured 225 spring chinook during the mainstem survey. Adults, designated as fish >56 cm FL (determined from post-season analysis of length frequency and coded-wire tag recoveries. The data used for the analysis were those collected during run-size-estimate studies (Chapter IV)) composed 81.3% of the spring chinook observed, while grilse (fish <56 cm FL) composed the remaining 18.7%. For comparison, the percentages of grilse for spring chinook sampled at JCW, and Trinity River Hatchery (TRH [RKM 180.1]) were 41.5% and 28.9%, respectively (Table 2). Data from WCW was not included in this comparison as only a small portion of the late spring chinook population was sampled there. There was a significant difference between the percentages of grilse sampled in the survey and at the two fixed sites (X²=53.4, df=2, P<0.0001). Mainstem spring chinook ranged in size from 41 to 101 cm FL, averaging 70.7 cm FL (Figure 3).

All chinook carcasses in the tributary surveys were recovered after 9 November 1992, so we assumed that no spring chinook spawned in the tributaries.

TABLE 2. Size composition of spring-run chinook salmon observed in the spawner survey and at two fixed locations in the mainstem Trinity River during the 1992-93 season.

		Junction City Weir		Trinity River Hatchery		Mainstem spawner survey
Grilse a/		272		533		42
Adults		384		1313		183
% Grilse		41.5%		28.9%		18.7%
a/ Spring-run chinook salmon < 56 cm FL were considered grilse based on a post-season analysis of length frequency and recovered coded-wire tags.

FIGURE 3. Fork length distribution, in 2-cm increments, of spring-run chinook salmon measured in the mainstem Trinity River during the 1992-93 spawner survey.

Fall-run Chinook Salmon

We measured 231 fall chinook carcasses during the mainstem survey this season. Based on a minimum size of 50 cm FL for adults, 92.2% of the fall chinook measured were adults and 7.8% were grilse (Table 3). The percentages of fall chinook grilse at the different sampling sites, including the tributary survey, ranged from 5.3% to 38.9%, and when tested for independence, the difference in grilse proportions between sites was highly significant (X²= 1468.22, df=4, P=0). Mainstem fall chinook ranged in size from 41 to 98 cm FL, averaging 72.4 cm FL (Figure 4).

We measured 36 fall chinook carcasses in the tributaries this year. Of these, 61.1% were adults and 38.9% were grilse (Table 3). Tributary fall chinook ranged in size from 39 to 90 cm FL, averaging 57.3 cm FL.

Coho Salmon

We measured 41 coho carcasses in the mainstem Trinity River. Adults, designated as fish >50 cm FL^3/, composed 95.1% of the coho measured, with grilse composing the remaining 4.9% (Table 4). The percentages of coho grilse at the different sampling sites ranged from 4.9% to 33.8% (Table 4), but the differences were not significant (X²= 34.89, df=3, P=0). Mainstem coho ranged in size from 41 to 84 cm FL, averaging 65.3 cm FL (Figure 5).

TABLE 4 Size composition of fall-run chinook salmon observed in the spawner surveys and at three fixed locations in the Trinity River basin during the 1992-93 season.

FIGURE 4. Fork length distribution, in 2-cm increments, of fall-run chinook salmon measured in the mainstem Trinity River during the1992-93 spawner survey.

TABLE 4. Size composition of coho salmon observed in the mainstem spawner survey and at three fixed locations in the Trinity River basin during the 1992-93 season.

FIGURE 5. Fork length distribution, in 2-cm increments, of coho salmon measured in the mainstem Trinity River during the 1992-93 spawner survey.

Sex Composition

Sex was determined only for carcasses observed during surveys in the mainstem Trinity River that were either unmarked condition-two, Program-marked, or flagged recoveries.

Chinook Salmon

We determined the sex of 522 adult chinook carcasses during the survey (212 spring-run and 310 fall-run). Of the adult spring chinook observed, 66.5% were females, while adult fall-run fish were 58.7% females. Overall, the weekly proportions of females seen in the survey were higher during the late and middle periods of each respective run (Figure 6). The seasonal trends in sex ratios noted in the previous three years' surveys showed females more predominant during the early and late weeks of the survey and lowest during the middle weeks (Zuspan 1992a, 1992b, 1994).

FIGURE 6. Proportions of female adult chinook carcasses observed in the mainstem Trinity River during the 1992-93 spawner survey.

A preponderance of adult females in the chinook run has been noted in all but two of the previous surveys. Female proportions have ranged from 73.6% to 25.8% (Appendix 6). Increased numbers of females among adult spawners result when more males than females return as grilse for a particular brood year.

Coho Salmon

We determined the sex of 51 coho, 17 (33.3%) of which were females. For comparison, 42%, 57%, 80%, and 60% of the coho examined in the 1988 through 1991 seasons, respectively, were females (Zuspan 1991, 1992a, 1992b, 1994).

Prespawning Mortality

Prespawning mortality was determined only for carcasses observed during surveys in the mainstem Trinity River that were either unmarked condition-two, Program-marked, or flagged recoveries.

Chinook Salmon

We determined the spawning condition of 185 adult female chinook salmon, including 51 spring-run and 134 fall-run fish. Prespawning mortality rates were 5.9% (3/51) and 0.7% (1/134) for female spring and fall chinook, respectively.

The overall female prespawning mortality rate for both races combined (spring- and fall-runs) was 2.2%. The lowest on record was 1.1% in 1991, with past prespawning mortality rates reported as high as 44.9% (Appendix 7).

Prespawning mortality of chinook in the Trinity River basin appears to be correlated to spawner escapement. Specifically, as spawner escapement increases so does prespawning mortality. The CDFG's Trinity River Project has developed chinook salmon escapement estimates for both runs of salmon in the Trinity River basin since 1978. Prespawning mortality was determined for the periods 1978 through 1982, and for 1987 to the present. During those periods, escapement has ranged from 6,135 to 100,913 while prespawning mortality rates have ranged from 1.1% to 44.9% (Appendix 7). With the exception of 1980, prespawning mortality generally increased with increasing escapement (Figure 7). ). The high prespawning mortality noted in 1980 may have been due to a sampling deficiency. During that year, only a total of 63 female chinook was checked for spawning condition. A regression analysis of escapement and prespawning mortality indicates a statistically significant correlation (R²=0.44, P=.026) even with the 1980 data included. Without the 1980 data, the statistical significance is much greater (R²=0.73, P=.001).

FIGURE 7. Comparison of adult chinook salmon natural spawner escapement and adult female chinook salmon prespawning mortality for the mainstem Trinity River, 1978-1982, and 1987-1992.

Coho Salmon

Seventeen adult female coho carcasses were examined for spawning condition during the survey. This sample size may not be adequate to accurately represent prespawning mortality. Of the coho examined, two (11.8%) of the fish had died prior to spawning (Appendix 4). For comparison, the prespawning mortality rates of adult female coho salmon were 25.6%, 6.2%, 13%, and 0% in 1988 through 1991, respectively (Zuspan 1991, 1992a, 1992b, 1994). Coho prespawning mortality was not reported in surveys prior to 1988.