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

Salmon Spawner Distribution

Salmon spawner distribution in the mainstem Trinity River is presented based on the seven-zone system first used in 1987 (Stempel, Appendix 1). The results from Zones 5, 6, and 7 were combined this year because too few flagged chinook were recovered in these individual zones. Distribution estimates are for adult fish only.

Chinook Salmon

Mainstem Trinity River. We examined 862 adult chinook salmon carcasses in the mainstem this season, excluding flag recoveries. The numbers of chinook salmon spawners ranged from 222 fish in Zone 2 to 124 fish in Zone 3 (Table 5). We recognized that carcass counts alone could not accurately describe distribution, because carcass recovery can vary from zone to zone, due to differences in stream morphology. Therefore, a recovery efficiency was calculated for each zone based on the ratio of flagged carcasses recovered to total carcasses flagged. This efficiency was used to expand the numbers of unflagged carcasses found in the respective zone, and obtain an overall weighted distribution and proportions of spawners in the entire survey area. Even based on the total number of chinook salmon recovered divided by the different recovery efficiency rates for each zone, the percent of chinook salmon spawners decreased downstream in successive zones below Zone 2 (Table 5). Spawner densities, based on expanded totals of unflagged carcasses in a zone and the length of the zone, was highest in Zones 1 and 3 (84.4 and 81.1 spawners/km, respectively), and decreased in a downstream direction (Table 5, Figure 8).

TABLE 5. Adult chinook salmon spawner distribution and estimated density by river zone during the 1992-93 Trinity River spawner survey.

Zonea/

Zone length ((km)

Number carcasses flagged

Flagged carcasses recovered

Recovery efficiency

Total unflagged observed b/

Expanded total c/

Percent distribution

Spawner density (fish/km) d/

1

3.2

59

35

59.3%

160

270

9.0%

84.4

2

7.9

99

41

41.4%

222

536

17.8%

67.8

3

10.2

60

9

15.0%

124

827

27.4%

81.1

4

10.4

70

20

28.6%

139

486

16.2%

46.7

5-7e/

31.7

103

25

24.3%

217

893

29.7%

28.2

Totals:

63.4

391

130


862

3,012

100%


Overall:




33.2%




47.5

a/ Zones described in Figure 1 and Table 1.
b/ Total adult chinook salmon observed, excluding flag recoveries.
c/ Computed from: (Total unflagged observed/(% flags recovered/100)).
d/ Computed from: Expanded total/Zone length (km).
e/ Zones combined because too few chinook carcasses were recovered to develop recovery efficiencies for individual zones.



FIGURE 8. Estimated adult chinook salmon spawner density by zones during the 1987 through 1992 mainstem Trinity River spawner surveys.

This pattern of relatively higher chinook salmon spawner concentrations in the upstream sections has been noted in all previous Project study years (Zuspan 1991, 1992a, 1992b, 1994), but was much less pronounced during the past two years. Spawners were much more evenly distributed throughout the mainstem during the most recent surveys (Figure 8).

It is possible that increases in river flow during the late summer and fall were responsible for the more even distribution of spawners. The flows averaged about 150 CFS higher this year (450 compared to 300 CFS), in an attempt to keep river temperatures within specified criteria; although, temperatures were not significantly lower than in previous years. However, higher flows probably increased holding and spawning habitats, allowing chinook salmon to spawn farther downstream. It should also be noted that decreases in spawner escapement over the last few years may somehow have caused spawners to distribute themselves more evenly. While there has been a steady decrease in spawner escapement, the densities of spawners has become less disproportionate between the downstream zones during the past two surveys (Figure 8).

A potential source of error in the estimates was the assumption that flagged chinook salmon carcasses were recovered only in the zone in which they were originally flagged. If flagged carcasses were recovered in downstream zones, it would tend to increase the efficiency estimate in the recovery zone while decreasing the estimate in the flagging zone.

To determine the extent that carcasses drifted from one zone to another, fish flagged in each zone were given a distinct hog ring color. Recoveries that were originally flagged in another zone were recorded as such. This season, all flags were recovered in the same zone in which they were originally flagged. This indicated that carcass drifting had no effect on chinook distribution estimates, similar to results in the 1990-91, and 1991-92 seasons (Zuspan 1992b, 1994). Even during the 1989-90 season the proportion of flags that drifted into other zones was still less than 1% (Zuspan 1992a).

Tributaries. Spawning adult chinook salmon made very limited use of tributaries this year. Few chinook salmon carcasses were observed this season, so we used redd counts to describe spawner distribution, as was the case during the 1990-91, and 1991-92 seasons (Zuspan 1992b, 1994).

We located 94 salmon redds in the nine tributaries surveyed this season. Since we could not differentiate a chinook from a coho salmon redd during the surveys, we used the relative proportion of chinook and coho salmon carcasses observed in the individual tributaries to apportion the redds by species. Based on this apportioning, there were an estimated 75.2 chinook salmon redds overall this season with individual tributary estimates ranging from 20.0 for Grass Valley Creek to 0.5 for Weaver Creek (Table 6).

TABLE 6. Observed salmon redd numbers and estimated distribution for the 1992-93 Trinity River tributary spawner survey.

Number observed

Proportional redd distributiona/

Tributary

Chinook carcasses

Coho carcasses

Redds

Chinook

Coho

Rush Creek

5

4

8

4.4

3.6

Grass Valley Creek

12

2

22

20.0

1.7

Indian Creek

1

1

7

4.0

3.5

Reading Creekb/

0

0

1

1.0

0.2

Browns Creek

4

0

16

16.0

0.0

Weaver Creek

1

1

1

0.5

0.5

Canyon Creek

8

2

12

10.0

2.4

N. Fork Trinity R.(NFTR)

4

0

11

11.0

0.0

E. Fork of the NFTR

9

1

16

14.0

1.6

Totals:

44

11

94



Overall:




75.2

18.8


a/ Computed by proportioning the redds observed by the numbers of each species observed. Chinook redds = Redds x chinook observed / (chinook observed + coho observed).
b/ Since no fish were observed in this creek, the redd proportioning was calculated by using the total chinook and coho for all creeks.

Coho salmon

Mainstem Trinity River. We observed 51 adult coho carcasses in the mainstem spawner survey this year, most of which were seen in Zones 1 and 2 (Table 7). Since coho were not flagged, we estimated the numbers of coho which spawned in each zone using the recovery efficiency for that zone developed from chinook salmon flag recoveries. Coho spawner density was highest in Zone 1 (6.9 fish/km) and ranged from 4.6 to 1.0 fish/km in the other zones (Table 7).

Tributaries. We observed 11 coho carcasses during the tributary surveys. They were seen in Weaver Creek, the East Fork of the North Fork Trinity River, Rush Creek, Grass Valley Creek, Indian Creek, and Canyon Creek. (Appendix 5). When the observed redds were apportioned by species, there were an estimated 18.8 coho redds overall in the tributary survey. The highest estimated number of redds (3.6) occurred in Rush Creek (Table 6).

TABLE 7. Adult coho salmon spawner estimated distribution and densities by river zone during the 1992-93 mainstem Trinity River spawner survey.

Zone a/

Zone length (km)

Total observed

Observation efficeincy b/

Expanded total c/

% of expanded total

Spawner density (fish/km)d/

1

3.2

13

59.3%

22

14.2%

6.9

2

7.9

15

41.4%

36

23.2%

4.6

3

10.2

2

15.0%

13

8.4%

1.3

4

10.4

3

28.6%

10

6.5%

1.0

5-7 e/

31.7

18

24.3%

74

47.7%

2.3

Totals:

63.4

51


155

100.0%


Overall:



33.2%



3


a/ Zones described in Figure 1 and Table 1.
b/ Observation efficiency equals the total recovery rate of flagged chinook salmon in each zone.
c/ Computed from: Total observed/(observation efficiency/100).
d/ Computed from: Expanded total/Zone length (km).
e/ Zones combined because too few coho carcasses were recovered to develop observation efficiencies for individual zones.

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