ANNUAL RUN-SIZE, HARVEST, AND SPAWNER ESCAPEMENT ESTIMATES FOR TRINITY RIVER BASIN CHINOOK AND COHO SALMON AND STEELHEAD (continued)
Run Timing. During the first week at WCW the 62 chinook salmon which were trapped appeared to be primarily spring-run fish. All of the chinook trapped after the first week were clearly fall chinook (Table 1).
The first spring chinook entered JCW 5 June (JW 23). The number of spring chinook trapped each week increased and peaked JW 27 (2-8 July) and decreased substantially during the next week although there were two minor peaks in the run during JW 30 (23-29 July) and JW 33 (13-19 August)(Figure 3). We considered the spring-run to be over JW 36 (3-9 September) at JCW. We trapped 310 spring chinook at JCW during the 1991-92 season (Table 1).
Size of Trapped Fish. The sizes of the spring chinook trapped at WCW and JCW, and that entered TRH were essentially the same (Table 2, Figure 4). Based on a moving average of 5, 1-cm increments, the nadir in the FL separating grilse and adult spring chinook was 53 cm at JCW (Figure 4). There was no nadir separating grilse and adult spring chinook at WCW or that entered TRH. However, the size separating grilse and adults of known-age, hatchery-marked spring chinook that entered TRH also appeared to be 53 cm FL (Appendix 2). Therefore, during the 1991-92 season, we consider spring chinook in the Trinity River basin <53 cm FL to be grilse, while adults are larger.
During the 1991-92 season, 11% of the spring chinook trapped at WCW and 8.1% of those trapped at JCW were grilse, similar to the proportion of spring chinook grilse in the TRH sample (10%) (Table 2). The low proportion of grilse is typical of the upper Trinity River basin spring run (Heubach 1984a, 1984b; Heubach et al. 1992a, 1992b).
Incidence of Tags and Hatchery Marks. None of the spring chinook salmon tagged at WCW were recaptured at the JCW during the spring run.
None of the spring chinook trapped at WCW were hatchery-marked, while 19 (6.5%) of the fish trapped at JCW were hatchery-marked (Table 2). The mean FL of the hatchery-marked spring chinook was over 3 cm less than the unmarked fish, although there were too few hatchery-marked fish trapped to test statistically (Table 3).
Of the 16 hatchery-marked spring chinook spaghetti tagged at JCW, six were subsequently recovered in the spawner survey or at TRH.
Two fish were from the 1987 brood year (BY), one fish each was from the 1986 and 1988 BYs, and two fish were without a CWT (Table 4).
Incidence of Gill-net and Hook Scars. Sixteen (25.8%) of the spring chinook trapped at WCW and 28 (9.0%) of the spring chinook trapped at JCW were gill-net scarred. At both weirs the mean FLs of the gill-net-scarred fish were larger than the non-gill-net-scarred fish, although in neither case were they statistically different (Table 3).
As in 1989-90 and 1990-91, we examined the tagging mortality and recovery at TRH of gill-net-scarred vs. non-gill-net-scarred spring chinook tagged at JCW (Tables 5 and 6). Two of the 28 (7.1%) Project-tagged fish with gill-net scars were recovered dead at the weir compared to 7 of the 282 (2.5%) non-gill-net-scarred fish. After correcting for the tagging mortality, five of the 26 (19.2%) gill-net-scarred spring chinook and 81 of the 275 (29.5%) non-gill-net-scarred fish were recovered at TRH. The differences in the tagging mortality and recovery rate of effectively tagged, gill-net-scarred and non-gill-net-scarred spring chinook were not statistically different (Tables 5 and 6). However, these results follow the trend observed in the last two seasons of slightly higher tagging mortality rates and lower hatchery recovery rates of gill-net-scarred than non-gill-net-scarred spring chinook (Heubach et al. 1992a, 1992b).
When we pooled the results of the tagging mortality of gill-net-scarred and non-gill-net-scarred spring chinook for the last three seasons, the difference was highly significantly (Table 5). However, the recovery rates of the effectively-tagged gill-net-scarred and non-gill-net-scarred spring chinook at TRH were not statistically different, even though in all years there was a slightly higher recovery rate of the non-gill-net-scarred fish (Table 6). We conclude that there has been a slightly higher tagging mortality of gill-net-scarred spring chinook at JCW during the last three seasons. The recovery rate of effectively-tagged gill-net-scarred spring chinook also appears to be less than the rate for non-gill-net-scarred fish, even after correcting for the differences in the tagging mortality of gill-net-scarred fish.
Only one spring chinook at WCW was hook scarred while 20 hook- scarred fish were trapped at JCW. Collectively, 14 of the fish had ocean-hook scars while seven were freshwater-hook scars. The mean FL of the hook-scarred spring chinook trapped at JCW was 6 cm greater than the non-hook-scarred fish, although the difference was not statistically significant (Table 3).
Run Timing. The fall run began at the WCW 27 August 1991 (JW 35). The numbers of fall chinook trapped decreased during the second week of trapping, then increased through JW 40 (1-7 October) when the run peaked (Figure 3). The fall run then decreased sharply through JW 42 (15-21 October) and gradually thereafter. We trapped the last fall chinook 29 November 1991 (JW 48), suggesting the run was over in the lower Trinity River when we removed the weir. We trapped 954 fall chinook at WCW during the 1991-92 season (Table 1).
The fall run began at JCW 10 September (JW 37), two weeks after it began at WCW. The fall run increased each week through JW 42 (15-21 October), decreased slightly the next week, and peaked JW 45 (5-11 November), five weeks after the peak at WCW (Figure 3). The numbers trapped each week decreased substantially during JW 46 (12-18 November) and gradually thereafter. We trapped the last fall chinook at JCW on 11 December (JW 50), two days before we removed the weir for the season. We trapped 489 fall chinook at JCW during the 1991-92 season (Table 1).
Size of Fish Trapped. The fall chinook trapped at WCW appeared slightly larger than those trapped at JCW (Table 7), although their mean FLs were not significantly different (t=0.86, p<0.05).
The size separating grilse and adult fall chinook was 51 cm FL at both weirs and at TRH. This season, we consider all fall chinook <51 cm FL to be grilse, whereas larger fall chinook are considered adults (Figure 5). Grilse composed 4.0% and 12% of the fall chinook trapped at WCW and JCW (Table 7), respectively, while at TRH, 7.6% of the fall chinook were grilse. The differences in the proportions of grilse and adult fall chinook at the two weirs and TRH were highly significantly (X2=10.0, p<0.01). The reason for the differences in the grilse/adult ratios at the three sites is unknown.
Incidence of Tags and Hatchery Marks. Forty-four WCW-tagged chinook were recaptured at JCW during the fall run (after 9 September 1991). Two of the fish were trapped and tagged at WCW as spring chinook, but they were recaptured at the JCW during the fall run. Excluding these two fish, the fall chinook took from 14 to 58 days to migrate to the JCW, with a mean of 29 days, for a mean migration rate of 3.1 km/d. The mean number of days (approximately four weeks) it took for the WCW-tagged fall chinook to migrate to the JCW is slightly less than the five weeks difference in the peaks of the fall run occurring at the two weirs. The mean migration rate of the fall chinook from WCW to the JCW this year was essentially identical to that in 1990 and slightly slower than the migration rate in 1989 (Heubach et al. 1992a, 1992b).
Seventy-nine (8.3%) and 42 (8.6%) of the fall chinook trapped at WCW and JCW, respectively, were hatchery-marked fish (Table 5). The mean FLs of the hatchery-marked fall chinook were slightly larger than the unmarked fish trapped at each weir, but the differences were not statistically significant (Table 3).
We recovered coded-wire tags from 32 of the 33 fall chinook that had been trapped and spaghetti-tagged at WCW and recovered in the carcass survey or recaptured at TRH. All but one of the CWT fall chinook were from the 1987 and 1988 BYs produced at TRH (Table 4). The majority (82.3%) of the fish had been released as yearlings. One CWT grilse, spaghetti tagged at WCW as a fall chinook was later discovered to be a spring-run fish.
We recovered coded-wire-tags from 14 of the 17 fall chinook that had been trapped at JCW and entered TRH. All but one of the CWT fish were from the 1987 and 1988 BYs produced at TRH (Table 4), the majority (70.5%) had been released as yearlings.
Incidence of Gill-net and Hook Scars. Gill-net scars were observed on 5.5% and 12.4% of the fall chinook trapped at WCW and JCW, respectively. The difference was significant (X2 = 13.9, p<0.01). The mean FLs of the gill-net-scarred fall chinook at WCW and JCW were not significantly different from the FLs of the non-gill-net-scarred fall chinook captured at the respective weirs (Table 3).
Because fewer gill-net-scarred fall chinook were seen at JCW than at WCW, we examined the recovery of WCW-tagged gill-net-scarred and non-gill-net-scarred fall chinook at JCW and TRH. The recovery of WCW-tagged gill-net-scarred and non-gill-net-scarred fall chinook at JCW was essentially the same at 4.6% and 4.9%, respectively. However, 30.4% of the effectively-tagged, non-gill-net-scarred fall chinook tagged at WCW were recovered at TRH compared to 18.5% of the gill-net-scarred fish, the difference being significant (X2=5.97, p<0.025).
We also compared the recovery rates at TRH of gill-net-scarred and non-gill-net-scarred fall chinook tagged at JCW. Eleven of the 27 (40.7%) gill-net-scarred fish and 159 of the 432 (36.8%) non-gill-net-scarred fall chinook were recovered at TRH. The difference was not statistically significant (X2=0.04, p>0.80).
The lower recovery rate of WCW-tagged, gill-net-scarred fall chinook at TRH compared to non-gill-net-scarred fish appears to be due to differences in their survival or behavior after these fish passed JCW, because there was no difference in the recovery rate of gill-net-scarred vs. non-gill-net-scarred fall chinook at JCW. Whatever the reason for the relatively low recovery rate at TRH of gill-net-scarred fish tagged at WCW, it did not occur with the gill-net-scarred fall chinook tagged at JCW.
There were no differences in the recapture rates of tagged gill-net-scarred and non-gill-net-scarred fall chinook salmon during the previous two seasons (Heubach et al. 1992a, 1992b), and we do not know the reason for the difference this year. However, recapture rates of the gill-net-scarred and non-gill-net-scarred fall chinook should be examined in future years to determine any effects the Indian gill-net fishery may have on the chinook fall-run.
Thirty (3.1%) of the fall chinook trapped at WCW and 18 (3.7%) of the fall chinook trapped at JCW were hook scarred. Most of the hook scars on fish from WCW were of ocean origin (63.3%), whereas most of the hook scars on fish from JCW were of freshwater origin (72.2%). The mean FLs of the hook-scarred fall chinook at the WCW and JCW were similar to the non-hook-scarred fish at the respective weir sites (Table 3).
Run Timing. We trapped the first coho at WCW on 16 September 1992 (JW 37). The coho catches increased gradually through JW 39 (24-30 September), and then rapidly through JW 42 (15-21 October), when the run peaked (Figure 6). The numbers of coho trapped decreased dramatically the next week and more slowly thereafter. While we did not trap any coho salmon during JWs 47 through 49 (19 November-9 December) at WCW, one coho was trapped the day before the weir was removed for the season. We trapped 604 coho salmon at WCW during the 1991-92 season (Table 8).
The first coho entered the JCW trap 11 October (JW 41), approximately four weeks after they initially appeared at the WCW. While the coho run peaked during JW 45 (5-11 November) three weeks after it occurred at the WCW, there was a second smaller peak during JW 47 (19-25 November) (Figure 6). For comparison, the difference in trapping peaks between the two weirs during the 1990-91 season was only one week (Heubach et al. 1992b). We trapped the last coho at the JCW on 6 December 1991, one week before trapping operation ended for the season. We trapped 222 coho at JCW during the 1991-92 season (Table 8).
Size of Fish Trapped. The size ranges and mean FLs of coho trapped at WCW and JCW were similar (Table 9). The size separating grilse and adult coho is based on the coho that were trapped at JCW and that entered TRH (Figure 7), because a nadir separating grilse and adults was not apparent at WCW. The nadir separating grilse and adult coho at the JCW and TRH was 49 cm FL (Figure 7). Therefore, in this report we consider all coho <49 cm FL grilse, while larger coho are considered adults. All of the hatchery-marked coho that entered TRH this season were <49 cm FL (Appendix 3).
Grilse coho comprised approximately 3.2% and 3.3% of the coho trapped at WCW and JCW, respectively, essentially the same as the fraction of those entering TRH (3.6%). This suggests the modifications made to the weir boat gates this year were effective in preventing coho <50 cm FL from passing through the weirs.
Incidence of Tags and Hatchery Marks. We recaptured 27 coho at JCW that had been tagged at WCW. Their mean migration time was 27 d, for a mean migration rate of 3.4 km/d. The mean number of days the coho were at liberty between the weirs is slightly greater than the three-week difference in the peaks in the coho runs at the two weirs.
We trapped two hatchery-marked grilse coho at WCW and one at JCW (Table 9). These fish were probably returning 1989 BY coho that had been released from TRH on 13 March 1991.
Incidence of Gill-net and Hook Scars. Gill-net scars were observed on 4.1% and 1.8% of the coho trapped at WCW and JCW, respectively. The mean FLs of the gill-net-scarred coho at WCW and JCW were not significantly different than the non-gill-net-scarred fish at each site (Table 3).
None of 27 coho tagged at the WCW that were recaptured at JCW were gill-net scarred. This finding does not appear to be related to survival of the gill-net-scarred coho however, because 32% (7/22) of the effectively-tagged gill-net-scarred and 29% (165/564) of the non-gill-net-scarred coho tagged at WCW entered TRH. Also, three of four gill-net-scarred JCW-tagged coho entered the hatchery.
We found 4.0% each of the coho trapped at WCW and JCW to be hook scarred. Collectively, 64% of the hook scars appeared to be of freshwater origin. The mean FLs of the hook-scarred and non-hook-scarred coho trapped at WCW and JCW were similar (Table 3).
Run Timing. We trapped steelhead during the first week (20-26 August 1991 [JW 34]) of operations at WCW and continued to catch them every week of the season there. The largest number of steelhead was trapped the first week followed by three weeks of progressively lower numbers (Figure 6). We trapped relatively large numbers of steelhead again at WCW during JWs 40 through 42 (1-21 October). The numbers of steelhead trapped peaked again in JW 44 (29 October-4 November) and generally declined through the end of the trapping season (13 December 1991). However, the steelhead run did not appear to be over when we removed the weir for the season. We trapped 638 steelhead at the WCW during the 1991-92 season (Table 10).
One steelhead entered the trap the first night of trapping at JCW, but we did not see another steelhead there until 26 June 1991 (JW 26). We trapped steelhead intermittently at JCW from JW 26 through JW 43 (25 June-28 October) (Figure 6). The steelhead run peaked JW 45 (5-11 November) and 47 (19-25 November 1991) at JCW and declined thereafter. We trapped 103 steelhead at JCW during the 1991-92 season (Table 10). It appeared that the coho and steelhead runs at WCW and JCW were synchronous, as they were in the 1990-91 season (Heubach et al. 1992b).
Size of Fish Trapped. The size ranges and mean FLs of steelhead trapped at WCW and JCW appeared similar (Table 11). Half-pounder steelhead (< 41 cm FL) made up 2.0% and 9.7% of the steelhead trapped at WCW and JCW, respectively. In contrast, approximately 22.2% of the steelhead that entered TRH were sub-adults (Figure 8). The higher proportion of steelhead <41 cm FL entering TRH in comparison to those trapped at the weirs is probably due to non-migrating resident steelhead entering the hatchery and not half-pounder steelhead passing the weirs.
Incidence of Tags and Hatchery Marks. We trapped 74 fin-clipped steelhead at WCW, 67% of which were from the 1988 BY, released from TRH in March 1990 (Appendix 4). Thirty-six fin-clipped steelhead were trapped at JCW, 36% of which were from the 1988 BY (Table 11).
The proportion of fin-clipped (TRH-produced) to non-fin-clipped steelhead (both naturally and hatchery-produced steelhead) was higher in the latter part of the steelhead runs at both weirs. For example, 17 (6.7%) of the 254 steelhead trapped at WCW through the mid-season nadir in JW 39 (24-30 September 1991) were fin clipped, while 57 (14.8%) of the 384 steelhead trapped after that period were fin clipped. The difference was significant (X2= 9.12, p<0.05). While only two (14.3%) of the 14 steelhead trapped at JCW through 16 September (JW 37) were fin clipped, 34 (38.2%) of the 89 were fin clipped after that week. Although this difference was not statistically significant (X2= 2.1, p<0.15), the trends at both weirs may indicate that the early portion of their steelhead runs were composed primarily of late-migrating spring-run steelhead, while the later migration period at both weirs were composed mostly of fall-run steelhead. For this report, however, we will consider all steelhead trapped as fall run.
The ranges in FLs and mean FLs of fin-clipped and non-fin-clipped steelhead trapped at WCW were essentially the same (Table 3). The mean FL of fin-clipped steelhead at JCW was 7.8 cm less than the non-fin-clipped steelhead, although the difference was not statistically significant (Table 3).
Incidence of Gill-net and Hook Scars. Twenty steelhead trapped at WCW had gill-net scars. The mean FL of the gill-net-scarred steelhead was slightly larger than that of the non-gill-net-scarred steelhead, but the difference was not significantly different (Table 3). Only three gill-net-scarred steelhead were trapped at JCW.
Hook scars were observed on 3.3% and 4.8% of the steelhead trapped at WCW and JCW, respectively. At both weirs the hook- scarred steelhead appeared to be slightly larger than the non-hook-scarred fish, although both differences were not significant (Table 3).
