Declining body size is believed to be a universal response to climate warming and has been documented in numerous studies of marine and anadromous fishes. The Salmonidae are a family of coldwater fishes considered to be among the most sensitive species to climate warming; however, whether the shrinking body size response

Land-use disturbances and associated losses in habitat quantity and quality negatively affected the Bonneville Cutthroat Trout (BCT) Oncorhynchus clarkii utah population in Bear Lake, Idaho-Utah, in the early 1900s. Bear Lake BCT follow an adfluvial life history strategy, and without access to suitable spawning habitat, the population of wild BCT was nearly extirpated by the early 1950s. In response to this decline, supplementation of the population with hatchery BCT began in 1973. Production of wild BCT was minimal until conservation efforts shifted towards improving fish habitat and access to spawning tributaries. In 2002, only 5% of the population consisted of wild fish; by 2017, nearly 70% of BCT in annual population surveys were wild. As a result, rule changes have been proposed to allow for regulated harvest of wild BCT. However, gaining a comprehensive understanding of the population dynamics of BCT in Bear Lake is critical before changes are made to management of the fishery. The objectives of this study were to describe the population dynamics of wild and hatchery BCT in Bear Lake and evaluate different management options. We evaluated population demographics of hatchery and wild BCT in Bear Lake and used age-structured population models to assess a variety of management scenarios associated with wild fish harvest regulations (e.g., bag limits). Bonneville Cutthroat Trout grew at relatively fast rates, and females began to mature at age 5. We observed considerable differences in the length and age structure of the hatchery population (i.e., exploited) versus the wild population (i.e., unexploited) of BCT. In general, BCT in Bear Lake were larger and older than Cutthroat Trout O. clarkii in other systems. The current rate of exploitation for hatchery BCT was estimated as 0.27 (i.e., two-fish daily limit). If

We used bomb calorimetry to quantify the energy density of three fish species endemic to Bear Lake, Utah-Idaho that were collected in 2020 – 2021. We collected Bear Lake Whitefish Prosopium abyssicola , Bonneville Whitefish P. spilonotus , and Bonneville Cisco P. gemmifer . We found that mean (± standard deviation) wet weight energy densities were 6,312 (± 760) joules per gram for Bear Lake Whitefish, 5,301 (± 778) joules per gram for Bonneville Whitefish, and 4,743 (± 443) joules per gram for Bonneville Cisco. We built linear mixed models and found relationships between energy density and dry matter ratio (i.e., ratio of dried weight to wet weight of a fish) for all three species, suggesting that the energy density of future samples collected in Bear Lake could potentially be determined from comparisons between the dried and wet weight of fishes belonging to these species. Our results will be useful for future bioenergetics modeling with these three Bear Lake endemic species, and potentially with others species in related genera that share similar feeding, behavior, and life history traits.