I continued my assignment through the 1992-93 season to compile, analyze, and report or edit back-year accumulations of file data. These data were collected during studies to determine if alternative hatchery practices could potentially increase survival to adulthood of salmon reared at Trinity River Hatchery. Reports on the first two Job VIII task studies have been completed, and previously summarized. The third and fourth studies were combined into one report and are summarized in this Chapter.
The third and fourth studies dealt with coho salmon, Oncorhynchus kisutch, reared at Trinity River Hatchery. The studies were conducted to determine if survival to adulthood (ages three- and four-year-old) could be increased by the following management options: (i) release of juvenile fish during the new moon nearest the vernal equinox and (ii) release of larger juvenile fish.
The results were as follows: (i) survival of hatchery-reared coho salmon was not significantly increased by releasing them on the new moon nearest the vernal equinox, and (ii) releases of smaller juvenile fish (33-41 g/fish [13.7-11.1 fish/lb]) survived better to adulthood than larger juveniles (56-123 g/fish [8.1-3.7 fish/lb]). Greater returns of smaller released fish were probably due to larger fish having a greater tendency to return as grilse.
1. To provide for the compilation, analysis, write-up or editing of multi-year accumulations of previously collected file data on Trinity River basin salmon and steelhead that are beyond the scope of current Project activities.
2. To provide timely, as-needed technical support to the Project Supervisor in responding to unprogrammed information and data analysis requests regarding Trinity River basin salmon and steelhead stocks.
The California Department of Fish and Game (CDFG) has been researching hatchery stocking and rearing practices that would increase contributions to fisheries and spawner escapements of coho salmon reared at Trinity River Hatchery (TRH). This study is a part of that ongoing effort.
In cooperation with the CDFG, Nishioka et al. (1989) conducted a study at TRH and Iron Gate Hatchery to find out if the new moon nearest the vernal equinox (March 22) was the optimum time to release juvenile coho salmon; hereafter, study groups released at this time will be referred to as the optimal lunar-phased group (OLPG). Their study at TRH included samples from the 1979 through 1982 brood years (BYs), but they did not include results of the 1980 and 1981 BYs in their report because El NiZo conditions had drastically reduced recovery rates for these two BYs. Based on their study results, they concluded: " . . . the percent recovery of the OLPG was significantly higher than or equal to any other group in three of four occasions at the two hatcheries". We also examined the results from 1980 and 1981 BYs, and agree that El NiZo did depress recovery rates. Still, we thought that the effects of El Nino should have been equal on all fish from the same BY. Therefore, the results from the 1980 and 1981 BYs could be used to evaluate lunar-phase releases, and those recoveries are analyzed in this report.
The effects of size-at-release on survival was studied as a result of earlier studies which showed that survival to adulthood of hatchery-reared chinook salmon, O. tshawytscha, and steelhead trout, O. mykiss was increased by releasing juveniles of these species at larger sizes. We conducted a study to find out if coho salmon performed similarly.
To test a particular attribute, portions of the annual hatchery production were divided into groups, that were tagged with a coded-wire tag (CWT) having a unique code and marked with an adipose (AD) fin clip. There was one exception to this procedure: a group from the 1976 BY was marked with both a left and right ventral fin clip, and not CWTed. Portions of the annual production from the 1976 through 1978 BYs were used to determine if survival to adulthood is affected by size-at- release. Portions of the annual production from the 1979 through 1982 BYs were used to determine if the new moon nearest the vernal equinox is the optimum time to release coho salmon reared at TRH.
Our analyses of survival as related to size-at-release and lunar-phase-when-released were based on recoveries of CWTed adult fish from ocean fisheries and TRH. CWTed fish, released as juveniles into the Trinity River near TRH, were recovered as two-, three-, and occasionally as four-year-old fish. Adults were defined as three- and four-year-old fish, although over 99% of the adult coho salmon population were three-year-olds. The number of CWTed fish of each group recovered in ocean fisheries was added to the number for that CWT group returning to TRH. This sum was then divided by the number stocked to calculate the recovery rate. Relative survival within each BY was then inferred from these calculated recovery rates.
We used the following steps to determine if the new moon nearest the vernal equinox was the optimum time to release coho salmon:
1. We tested the hypotheses that there were no differences among the adult (ages three- and four-year-old) recovery rates of five groups released at various lunar phases. We tested for differences with a contingency table analysis at the 0.05 level of significance using the following formula (Zar 1984, p. 400-401):
2. We carried out a Tukey-type multiple comparison test (Zar 1984, p. 401-402) at the 0.05 level of significance to make one-on-one comparisons between the adult recovery rate of the OLPG and each of the groups representing other lunar phases.
There were not enough samples to apply tests of significance to size-at-release results; therefore, only subjective comparisons were made. Ocean catch results of only two BYs (1977 and 1978) were available for analysis due to use of different marks on the 1976 BY groups, which would not have been equally identifiable in ocean fisheries. Hatchery return results were compared for all three BYs, as all fish entering TRH were carefully examined for any marks. The larger juvenile fish used in this portion of the study ranged from 56-123 g/fish (8.1-3.7 fish/lb) when released and the smaller juvenile fish ranged from 32-41 g/fish (13.9-11.1 fish/lb).
Based on contingency table analysis of the groups representing various moon phase releases, we concluded there were significant differences among survival to ages three years and older for all BYs (P2 = p<0.05).
Results using the Tukey-type comparison test to find differences between the OLPG and groups released during other lunar phases were as follows (Figure 1):
1. 1979 BY - The survival of the OLPG was significantly greater than those of all other groups.
2. 1980 BY - The survival of the OLPG was less than those of the two groups released later, but the differences were not statistically significant. The OLPG survival was significantly greater than the earlier released groups.
3. 1981 BY - The survival of the OLPG was less than those of all other groups, and there was a statistically significant difference between it and the latest group released.
4. 1982 BY - The survival of the OLPG was greater than those for all other groups, but the differences between it and the groups released later were not statistically significant. The differences in survival were statistically significant between the OLPG and the earlier released groups.
FIGURE 1. Recovery rates for coded-wire-tagged coho salmon releaed on various moon phases.
The ocean recovery rate of adults was greater for smaller juvenile coho salmon released from the 1977 BY, and for larger juveniles released from the 1978 BY. No comparisons of ocean catch rates were made for the 1976 BY due to the use of different fin clips. Total recovery rates (ocean plus TRH recoveries) of adults were greater for the smaller fish released from the 1977 and 1978 BYs.
Adult hatchery return rates were greater for the smaller juvenile fish released in all three BYs. The grilse hatchery returns of larger released juveniles were several times greater in all BYs. These results suggest that smaller fish survived better to adulthood due the tendency of juveniles released at a larger size to return primarily as two-year-olds (Figures 2 and 3).
The following two assumptions were the basis for the hypothesis that the new moon nearest the vernal equinox is the optimum time to release coho salmon: (i) prominent peak levels of plasma thyroxin (T4) occur on the new moon nearest the vernal equinox, and (ii) survival is directly related to seawater adaptability. However, Nishioka et al. (1989) did not observe a single prominent peak of new-moon-associated T4 rise in either the 1979 or 1982 BYs as had been observed earlier by Grau et al. (1981).
Other studies have also indicated these assumptions may not be valid. After examining the relationship between coho salmon survival to adulthood and T4 concentration or gill (Na+K)-ATPase activity at two Oregon hatcheries, Ewing et al. (1985) concluded these relationships were poor predictors of future survival. They suggested other factors, such as ocean upwelling, may have greater effects on survival. Based on their study results, they concluded the most reliable index for predicting optimum-time-of release was a photoperiod-dependent index that does not vary with hatchery conditions (i.e., calendar dates).
Morley et al. (1988) reached a similar conclusion. Based on observation of coho salmon reared at Quinsam Hatchery, British Columbia, they concluded differences among returns of groups released at four dates (April 20, May 10, May 30, and June 19) were not due to changes in seawater adaptability.
The results from the size-at-release portion of our study suggests that survival to adulthood is greater for smaller juvenile coho salmon (32-41 g/fish [13.9-11.0 fish/lb]) than for larger juveniles (56-123 g/fish [8.1-3.7 fish/lb]). Larger juveniles returned as grilse at rates three to eight times greater than smaller fish, thereby reducing the potential adult population. These results are consistent with observations of Morley et al. (1988). From their study of fish ranging from 20 to 31 g/fish (22.6-14.6 fish/lb) at release, they concluded that the returning percentages of grilse increased as size-at-release of fish increased.
Both Ewing et al. (1985), and Morley et al. (1988), in their respective studies, concluded that June was the optimum time to release coho salmon from the hatcheries. Unlike hatcheries in the Pacific northwest, June is not the most favorable time to release coho salmon reared at TRH. Due to warmer available water temperatures, coho salmon reared at TRH are likely to grow faster than coho salmon reared at hatcheries in the Pacific northwest. As a result, coho salmon held to June at TRH would probably be larger than the optimum release size.
We concluded that the new moon nearest the vernal equinox may not be the optimum time to release coho salmon. The relationship between seawater adaptability at the time of release and survival to adulthood is presently unclear. There may be factors of equal or greater importance affecting survival other than physiological readiness. Physiological changes measured in the hatchery may not be good predictors of what may begin to occur after fish are released from the hatchery and start to actively emigrate to the ocean.
Ewing, R. D., A. R. Hemmingsen, M. D. Evenson, and R. L. Lindsey. 1985. Gill (Na+K)- ATPase activity and plasma thyroxine concentrations do not predict time of release of hatchery coho (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha) for maximum adult returns. Aquaculture, 45:359-373.
Grau, E. G., W. W. Dickoff, R. S. Nishioka, H. A. Bern, and L. E. Folmar. 1981. Lunar phasing of the thyroxine surge preparatory to seaward migration of salmonid fish. Science, 211:607-609.
Morley, R. B., H. T. Bilton, A. S. Coburn, D. Brouwer, J. Van Tine, and W. C. Clarke. 1988. The influence of time and size at release of juvenile coho salmon (Oncorhynchus kisutch) on returns at maturity: Results of three brood years at Quinsam Hatchery, B. C. Can. Tech. Rep. Fish. Aquat. Sci. No. 1620. 120 p.
Nishioka, R. S., E. G. Grau, H. A. Bern, R. J. Lin, P. M. Hubbell, A. C. Knutson, C. Hiser, D. Maria, M. Rightmier, and W. Jochimsem. 1989. Effect of lunar-phased releases on adult recovery of coho salmon from Trinity River and Iron Gate hatcheries in California. Aquaculture, 82:355-365.
Zar, J. H. 1984. Biostatistical Analysis. (2nd ed.), Prentice Hall, Englewood Cliffs, New Jersey. 718 p.
