Understanding age and growth of fishes is critical for making meaningful management decisions. Obtaining useful information is dependent on using the best structure (e.g., scale, otolith). The objective of this study was to evaluate precision and reader confidence in age estimates from sagittal otoliths (i.e., whole, sectioned) and scales for Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri collected from Henrys Lake, Idaho. We also sought to compare growth estimates among structures sampled during annual gill net surveys in May 2019 and 2020. We removed sagittal otoliths and scales from 416 Yellowstone Cutthroat Trout. Two readers without prior knowledge of fish length independently aged scales, whole otoliths, and sectioned otoliths. Each reader also provided a confidence rating of 0 (not confident) to 3 (completely confident). Percent exact agreement between readers was highest for sectioned otoliths (85.3%), followed by scales (68.5%) and whole otoliths (66.1%). Average confidence rating was highest for sectioned (mean ± SD = 2.2 ± 0.6) and whole (1.4 ± 0.5) otoliths and lowest for scales (1.0 ± 0.2). Among structures, percent exact agreement (i.e., consensus age) was highest between whole and sectioned otoliths (66.7%), followed by scales and sectioned otoliths (58.9%). Exact agreement was lowest between scales and whole otoliths (51.2%). Differences in back-calculated length at age estimates between sectioned otoliths and scales were minimal, particularly for ages 1–4. Although sectioned otoliths required more time to prepare than scales or whole otoliths, sectioned otoliths produced the most precise age estimates for Yellowstone Cutthroat Trout, with the highest reader confidence.

We evaluated the effects of air exposure on Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri caught and released in a cold-water stream with elevated water temperatures (i.e., > 14°C) in southeastern Idaho. Anglers caught fish in a 2.3-km section of Fall Creek, Idaho, during August 2018. Sampled fish remained underwater while we measured and then tagged them with T-bar anchor tags. We exposed fish to air for 0, 30, or 60 s and then released them at the point of capture. We continuously monitored temperature during the study period. Water temperatures during the study varied from 10.0 to 19.7°C and averaged 14.9°C (SE = 0.08). In total, anglers caught 161 Yellowstone Cutthroat Trout over 10 d. Of those fish, we did not expose 54 to air; we exposed 54 to air for 30 s, and 53 for 60 s. We used electrofishing to recapture tagged fish and estimate relative survival. Relative survival was highest for fish exposed to air for 60 s (0.40 [SE = 0.25]) followed by 0 s (0.35 [SE = 0.25]) and 30 s (0.30 [SE = 0.27]), but differences were not statistically significant. Results from this study are consistent with other air-exposure studies suggesting that air exposure of 60 s or less is not likely a concern in Yellowstone Cutthroat Trout fisheries. Releasing fish as quickly as possible is always encouraged, but management regulations restricting air exposure seem unnecessary given the collective body of field-based research on air exposure. Nevertheless, similar studies on other systems and species are warranted.

Yellowstone Cutthroat Trout (YCT) Oncorhynchus clarkii bouvieri is a species with significant ecological and recreational value.  In many YCT fisheries, managers are tasked with balancing angler expectations and fish conservation.  Henrys Lake supports a popular trophy trout fishery, but the increase of nonnative Utah Chub Gila atraria has caused concern for YCT.  Long-term trends in abundance, length structure, body condition, and growth of YCT were summarized to evaluate the effect of Utah Chub.  Additionally, we investigated abiotic and biotic factors influencing YCT.  Archived hard structures were examined to provide a comprehensive evaluation of changes in age and growth of YCT in the system.  Stocking records and catch rates of Utah Chub and trout in Henrys Lake were used as covariates to explain changes in YCT catch rates and growth.  Catch rates varied from 1.5 – 15.4 YCT per net night during the 2002 – 2020 sampling period, but no consistent patterns were identified.  Length structure was consistently dominated by stock- to quality-length fish and few fish > 600 mm TL were captured.  Relative weight of YCT has decreased from a mean ( SD) of 115.916.5 in 2004 to 93.2 8.2 in 2020.  Age of YCT varied between 1 and 11 years; fish captured during 2010 to 2020 were the oldest.  The majority of fish sampled were age-4 and younger.  Total annual mortality of age-2 and older YCT was higher than other Cutthroat Trout populations (i.e., 0.70 during 2002 to 2010 and 0.60 during 2011 to 2020).  Based on regression models, we identified positive relationships between catch rates of YCT, Brook Trout Salvelinus fontinalis, and Rainbow Trout Oncorhynchus mykiss × YCT hybrid trout.  Negative relationships were observed between growth of YCT and abundance of Utah Chub and Brook Trout.  Although negative relationships were identified, YCT growth in recent decades is as fast as or faster than earlier time periods.  Results from this research suggest that major changes in YCT population dynamics are not evident over the last 20 years.  This study provides insight into the factors influencing an adfluvial trout population.  In particular, results from this research may be useful for managers of systems where Utah Chub have been introduced.

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Henrys Lake, Idaho, supports a popular fishery for Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri and Yellowstone Cutthroat Trout × Rainbow Trout O. mykiss hybrids. A majority of the adult population of fish in Henrys Lake are of hatchery origin that were stocked as fingerlings. The fishery is closed to angling during the late winter and spring months, but fisheries managers are considering opening the fishery year-round with catch-and-release-only regulations or with a two-fish bag limit during the extended season. However, there is concern that the proposed management actions may negatively affect the current fishery. Therefore, we developed an integrated catch-atage model to estimate population parameters for trout in Henrys Lake and used a simulation model to evaluate alternative management actions. Results of this study suggest that catch and release of both Yellowstone Cutthroat Trout and hybrids would increase and that abundance of trout in the spring (i.e., the start of the traditional season) would decrease under both proposed bag limits. Losses in abundance can be mitigated by stocking additional fish as long as no more than approximately 1,520,000 Yellowstone Cutthroat Trout are stocked annually. If catch-and-release-only regulations are implemented during the newly proposed season, total harvest is expected to decrease compared to the current fishery due to additional catch-and-release mortality. Ultimately, managers will need to prioritize harvest or catch-and-release opportunity, both of which provide additional utility to anglers, when choosing how to proceed with bag limit regulations.Realized outcomes of recreational fisheries management actions at the population level are a result of their effect on population dynamic rates, including recruitment, growth, natural mortality, and fishing mortality (Hilborn and Walters 1992). Each dynamic rate can be affected by biotic or abiotic factors that may or may not be under the