LIFE HISTORY, DISTRIBUTION, RUN SIZE, AND HARVEST OF SPRING CHINOOK SALMON IN THE SOUTH FORK TRINITY RIVER BASIN (continued)
The following paragraph repeats results from the 1991-1992 Annual Report (Dean 1994) to allow the reader to follow the 1992 spring chinook cohort through the summer and fall covered in this report, and to more clearly understand our methodologies and results.
During the 1992 season we operated the Gates Weir for 64 days, from 27 April through 7 July 1992. During this period both immigrant and emigrant traps were maintained. Late in the trapping period we were forced to suspend trapping operations intermittently due to excessively warm minimum water temperatures. We captured, marked, and released 39 adult and 9 grilse spring chinook, 1 unspawned adult winter-run and 15 adult spring-run steelhead from the immigrant trap. One captured spring chinook escaped just prior to tagging, but scales and other data were obtained. Therefore, we captured a total of 49 spring chinook. Thirty-nine spring chinook were tagged with anchor tags and marked with a 2LV fin clip, and nine were implanted with radio tags and given a 2RV fin clip. We captured, examined, and released 65 out-migrant (spawned) adult winter-run steelhead from the emigrant trap (Table 1).
TABLE 1. Trapping summary for the Gates Weir by Julian week from 27 April through 7 July 1992.
|
Immigrant trap |
Emigrant trap |
||||||
|
Spring-run chinook salmon |
Steelhead | ||||||
|
Julian week |
Start date |
Adults |
Grilse a/ |
Winter-run b/ |
Spring-run c/ |
Spawned fall and winter-run steelhead |
|
|
17 |
4/23/92d/ |
0 |
0 |
1 |
1 |
0 |
|
|
18 |
4/30/92 |
1 |
0 |
0 |
3 |
22 |
|
|
19 |
5/07/92 |
1 |
1 |
0 |
1 |
33 |
|
|
20 |
5/14/92 |
9 |
0 |
0 |
0 |
5 |
|
|
21 |
5/21/92 |
8 |
0 |
0 |
0 |
2 |
|
|
22 |
5/28/92 |
7 |
1 |
0 |
0 |
1 |
|
|
23 |
6/04/92 |
6 |
1 |
0 |
0 |
1 |
|
|
24 |
6/11/92 |
2 |
1 |
0 |
2 |
0 |
|
|
25 |
6/18/92 |
5 |
0 |
0 |
1 |
0 |
|
|
26 |
6/25/92 |
0 |
0 |
0 |
2 |
1 |
|
|
27 |
7/02/92 |
1 |
5 |
0 |
5 |
0 |
|
|
Totals: |
40 |
9 |
1 |
15 |
65 |
||
|
a/ Grilse were chinook measuring < 55 cm, adults were > 55 cm. b/ Winter-run steelhead were upstream-migrating, sexually mature fish. c/ Spring-run steelhead were upstream-migrating, sexually immature fish. d/ Trapping actually began on 4/27/92. | |||||||
In 1992, we began catching spring chinook at the Gates Weir during the first week of May, only a few days after installation was completed. The run reached a peak from mid- through late-May (Table 1). We continued to catch fish until early July, when we were forced to remove the weir due to excessively warm minimum water temperatures (>21 oC). During snorkel and pool follow-up observations, we saw that some spring chinook continued to enter the SFTR through July and into August. Therefore, the run timing for SFTR spring chinook in 1992 was early May through early August.
Spring chinook captured at the Gates Weir in 1992 averaged 59.8 cm FL (" 9.5 cm SD) (Figure 3). TFIP had previously established 55 cm FL as the length separating adults and grilse in the mainstem Trinity River. Based on our scale analyses, we have revised this cut-off to 53 cm FL for SFTR spring chinook (see Scale Analysis, page 213). Next season we will use this figure to separate adult and grilse chinook captured at the Gates Weir.
For chinook captured and sexed at the Gates Weir in 1992, 32 (65%) were females and 17 (35%) were males. The percentage of males was slightly higher than last year, but still surprisingly low. Smaller grilse may have escaped capture at the Gates Weir at a higher rate than larger adults, accounting for the low number of males. Of chinook re-captured and sexed at the Forest Glen recovery weir in 1992, six (40%) were females and nine (60%) were males (sex not determined for five fish).
