Previous studies conducted at the Cle Elum Spring Chinook Salmon Supplementation Hatchery in Washington State demonstrated that 37-49% of the male Chinook salmon Oncorhynchus tshawytscha released from this facility in its first years of operation precociously matured at age 2 rather than the more typical age 4. We examined the effects of altering seasonal growth rate on the incidence of age-2 male maturation in an experimental subset of that population and compared their physiological development (size, growth rate, condition factor, whole-body lipid, gill Na þ ,K þ -ATPase activity, and plasma insulin-like growth factor-I [IGF-I]) with that of both hatchery (production) and wild fish. Altering summer and autumn rations resulted in four growth trajectories with the following size and precocious male maturation rates: the high summerÀhigh autumn growth trajectory produced fish averaging 25 g and 69% precocious maturation; the high summerÀlow autumn trajectory yielded fish that averaged 18 g and exhibited 58% precocious maturation; the low summerÀhigh autumn trajectory produced 18-g fish with 51% precocious maturation; and the low summerÀlow autumn trajectory yielded fish averaging 16 g and 42% precocious maturation. Production fish averaged 22 g and exhibited a 53% precocious maturation rate. The high summer growth treatments and production fish were largest among all groups and had higher plasma IGF-I, adiposity levels, and precocious male maturation rates than did the low summer growth treatments. Wild fish were significantly smaller and leaner and had much lower plasma IGF-I levels than all other groups. Gill Na þ ,K þ -ATPase activity was not different between groups, suggesting that there was no differential effect on smoltification. Growth modulation reduced the precocious male maturation rate by 39% among experimental treatments and by 21% between production fish and the lowÀlow treatment. However, the maturation rate and adiposity of hatchery fish differed markedly from those of wild fish, suggesting that more dramatic alterations of rearing regime may be required to further reduce the prevalence of this phenotype in cultured fish.

In male Chinook Salmon Oncorhynchus tshawytscha, age of maturation is phenotypically plastic, occurring at age 1 (referred to as precocious parr or microjack), age 2 (minijack), age 3 (jack), age 4, or age 5. Microjacks and minijacks are thought to forego migration to the ocean as smolts, instead remaining in headwaters and employing a “sneaking” strategy to fertilize eggs. We compared the prevalence of minijacks (minijack rate) among hatchery‐ and natural‐origin spring Chinook Salmon from the Yakima River, Washington, over seven brood years (2001–2007). We quantified minijack rates and sex ratios in the hatchery population prior to release and during out‐migration at a trap located 230 km downstream. Within this time period, we also monitored minijack rates in a 3‐year (brood years 2002–2004) growth study designed to reduce minijack production at the hatchery. Minijacks made up an average of 41% of the male population in the hatchery, but annual minijack rates varied in response to the growth rate or fish size at release. Average minijack rate was approximately 20% among out‐migrating hatchery fish, about half the rate found prior to release. Among out‐migrants, minijack rates of hatchery fish were approximately 10 times those of natural‐origin fish, but sex ratios were significantly skewed toward females in both hatchery‐ and natural‐origin groups. Data from this study and related studies suggest that the predominant age of early male maturation in the Yakima River and similar rivers is age 2 (minijack) in hatchery fish and age 1 (microjack) in natural‐origin fish. Based on this and other studies, we now recognize three minijack life history types in spring Chinook Salmon: resident, fluvial, and anadromous, depending on the migration pattern exhibited in the spring and summer. Finally, we discuss the broader impacts that high minijack production may have on the establishment of size‐at‐release targets for salmon supplementation programs in the future.

The Cle Elum Supplementation and Research Facility in the Yakima River basin, Washington, is an integrated spring Chinook Salmon Oncorhynchus tshawytscha hatchery program designed to test whether artificial propagation can increase natural production and harvest opportunities while keeping ecological and genetic impacts within acceptable limits. Only natural‐origin (naturally spawned) fish are used for hatchery broodstock. Spawning, incubation, and early rearing occur at a central facility; presmolts are transferred for final rearing, acclimation, and volitional release at sites adjacent to natural spawning areas, where returning adults can spawn with natural‐origin fish. The first wild broodstock were collected in 1997, and age‐4 adults have returned to the Yakima River since 2001. An unsupplemented population in the adjacent Naches River watershed provides a reference for evaluating environmental influences. The program has been comprehensively monitored from its inception. A synthesis of findings, many already published, is as follows: supplementation increased the harvest, redd counts, and spatial distribution of spawners; natural‐origin returns were maintained; straying to nontarget systems was negligible; natural‐origin females had slightly higher breeding success (production of surviving fry) in an artificial spawning channel, while the behavior and breeding success of natural‐ and hatchery‐origin males were similar; hatchery‐origin fish showed differences in morphometric and life history traits; high rates of hatchery age‐2 (minijack) production were reported, but the observed proportions of out‐migrating juvenile and adult (ages 4 and 5) returning males were comparable for hatchery‐ and natural‐origin fish; hatchery smolts did not affect the levels of pathogens in natural smolts; and the ecological interactions attributed to the program were within adopted guidelines. Continued study is required to assess the long‐term impacts on natural production and productivity.

Abstract.-We tagged juvenile upper Yakima River hatchery spring Chinook salmon Oncorhynchus tshawytscha with passive integrated transponder (PIT) and coded wire snout tags in a double-tag study to test the assumptions that tags are not lost and do not affect postrelease survival, behavior, or growth. The average loss of PIT tags was 2.0% (95% confidence interval [CI] ¼ 0.7-3.2%) in juveniles before release and 18.4% in recaptures returning 6 months to 4 years after release (95% CI ¼ 17.2-19.5%). Adult tag losses were not significantly correlated with age of return (analysis of covariance, P ¼ 0.40), indicating that the majority of PIT tag loss had occurred within the first 6 months after release. Smolt-to-adult recruit survival (SARS) of PIT-tagged fish was significantly lower (P , 0.05) than that of non-PIT-tagged (NPT) fish because of tag loss and reduced survival, resulting in an average underestimate of SARS of 25.0%. After correcting for tag loss, we estimated PIT tag-induced mortality to be as great as 33.3% with a mean of 10.3% over all brood years (P , 0.05). Mean lengths and weights of PIT-tagged adults were less than those of NPT adults in all age comparisons. However, only age-4 PIT-tagged adults were significantly smaller than NPT fish of the same age (mean length difference ¼ 1.1 cm; mean body weight difference ¼ 0.1 kg; analysis of variance, P , 0.05). There was no significant difference between migration timing of PIT-tagged and NPT adults within the upper Yakima River (MannWhitney test, P . 0.09). Given the widespread and increasing use of PIT tags, and their use in calculating critical estimators related to salmonid life history of Endangered Species Act populations, the effects of using PIT tags must be quantitatively considered under actual study conditions and, if necessary, be accounted for.

We found insufficient evidence to conclude that seminatural treatment (SNT; i.e., rearing in camouflage-painted raceways with surface and underwater structures and underwater feeders) of juvenile Chinook salmon Oncorhynchus tshawytscha resulted in higher survival indices than did optimum conventional treatment (OCT; i.e., rearing in concrete raceways with surface feeding) for the specific treatments and environmental conditions tested. We reared spring Chinook salmon from fry to smolt in paired raceways under the SNT and OCT rearing treatments for five consecutive years. For four to nine SNT and OCT raceway pairs annually, we used passive integrated transponder, coded wire, and visual implant elastomer tags to compare survival indices for juvenile fish from release at three different acclimation sites 340-400 km downstream to passage at McNary Dam on the Columbia River, and for adults from release to adult return to Roza Dam in the upper Yakima basin. The observed differences in juvenile and adult survival between the SNT and OCT fish were either statistically insignificant, conflicting in their statistical significance, or explained by significant differences in the presence of the causative agents of bacterial kidney disease in juvenile fish at release.