Climate warming has yielded earlier ice break‐up dates in recent decades for lakes leading to water temperature increases, altered habitat, and both increases and decreases to ecosystem productivity. Within lakes, the effect of climate warming on secondary production in littoral and pelagic habitats remains unclear. The intersection of changing habitat productivity and warming water temperatures on salmonids is important for understanding how climate warming will impact mountain ecosystems. We develop and test a conceptual model that expresses how earlier ice break‐up dates influence within lake habitat production, water temperatures and the habitat utilized by, resources obtained and behavior of salmonids in a mountain lake. We measured zoobenthic and zooplankton production from the littoral and pelagic habitats, thermal conditions, and the habitat use, resource use, and fitness of Brook Trout (Salvelinus fontinalis). We show that earlier ice break‐up conditions created a "resource‐rich" littoral–benthic habitat with increases in zoobenthic production compared to the pelagic habitat which decreased in zooplankton production. Despite the increases in littoral–benthic food resources, trout did not utilize littoral habitat or zoobenthic resources due to longer durations of warm water temperatures in the littoral zone. In addition, 87% of their resources were supported by the pelagic habitat during periods with earlier ice break‐up when pelagic resources were least abundant. The decreased reliance on littoral–benthic resources during earlier ice break‐up caused reduced fitness (mean reduction of 12 g) to trout. Our data show that changes to ice break‐up drive multi‐directional results for resource production within lake habitats and increase the duration of warmer water temperatures in food‐rich littoral habitats. The increased duration of warmer littoral water temperatures reduces the use of energetically efficient habitats culminating in decreased trout fitness.

Population connectivity between resident and migratory cutthroat trout (Oncorhynchus clarkii ssp.) is understudied, but has implications for population viability and management. We examined evidence for stream residency, studied the spatial patterns of stream use by adfluvial and stream-resident trout, and measured migration rates with changing stream depth for Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) in the Summit Lake Basin, Nevada (USA). Passive integrated transponder technology and a fry trap were used to track fish movements and identify the distribution of resident and adfluvial trout. Stream residents were distributed throughout the network. Adfluvial spawners concentrated in lower reaches, but also migrated up to 12.9 km. Adfluvial juveniles migrated to the lake from lower reaches and from upstream of adfluvial spawners. High stream depths coincided with more adfluvial juveniles migrating to the lake and more adfluvial spawners moving into the stream, which led to more accessing the upper watershed. This work shows that connectivity is central to adfluvial–resident Lahontan cutthrout trout population dynamics and may lead to increased probability of persistence — a characteristic of these isolated, threatened trout populations.

This work provides an overview of the use of small unmanned aircraft systems for freshwater fisheries survey and fish identification. As an example, a series of river reaches in Mongolia was surveyed for identification and sizing of the endangered Taimen Hucho taimen, the world's largest salmonid. Using polarized video imagery, Taimen were positively identified in depths of over 2 m. River reaches were chosen for survey to include likely Taimen holding grounds as well as areas that were unlikely Taimen habitat. Large areas of river reaches were quickly surveyed with video imagery stored for analysis. Using land‐based targets for sizing and flying autonomous search patterns, we found that Taimen were easily identifiable based on their swimming patterns and could be remotely sized; furthermore, the fish did not appear to be disturbed by the presence of overhead aircraft. Lessons learned from the experiments and recommendations for future advances are provided. The use of small unmanned aircraft systems for fisheries is shown to be a novel and inexpensive alternative to traditional fisheries survey methods.

Summit Lake, nevada (USA) is the last high-desert terminal lake to have a native self-sustaining population of threatened Lahontan cutthroat trout (Oncorhynchus clarkii henshawi). from spring 2015 to fall 2017, we quantified adult abundance and survival and the total annual spawning run. Abundance and survival were estimated with mark-recapture using pit tags, and the annual spawning run was estimated with PIT tag detections and counts of spawners. Adult abundance fluctuated from 830 (95% CI 559-1248) to 1085 (95% CI 747-1614), with no overall temporal trend, as a decrease in male abundance was generally offset by an equal increase in female abundance. Estimated mean adult survival was 0.51 (95% CI 0.44-0.58). The spawning run increased from 645 (2015) to 868 (2016), but then decreased slightly to 824 (2017, mean = 789 ± 118). Female spawners increased in 2016 but decreased slightly in 2017, whereas male spawners decreased each year. In addition, the proportion of adults that spawned each year increased overall. our study suggests that the adult population remained stable although most of the study period included the recent, severe regional drought in the western United States (2012-2016). Amid the backdrop of global biodiversity decline, North American freshwater fauna is declining five times faster than terrestrial fauna, including current extinction rates of freshwater fish 877 times greater than background rates 1-3. Since the mid-1800s, habitat loss, overfishing and invasive species have severely altered western United States (US) freshwater fish communities 4. Today climate change predictions for the large expanse of mountain ranges in the western US (increased climatic variability that will increase drought frequency, duration, and severity, and shift precipitation to more rain and less snow) threaten to compound the above disturbances 5-8. These legacy, current and future disturbances combine into a formidable challenge for conserving western US freshwater fish biodiversity, often necessitating active management of fisheries that are susceptible to further decline and localized extinctions 9. Cutthroat trout (Oncorhynchus clarkii spp.) are salmonids native to the coastal and inland waters of western North America 10. Consisting originally of approximately 14 subspecies, the historic distribution of cutthroat species ranged from Alaska to southern Texas and the Pacific coast to the Rocky Mountains 10,11. Distribution and abundance of many subspecies have declined over the past century. Two subspecies are extinct and three subspecies are on the US endangered species list 10,12. Cutthroat trout population dynamics research has been concentrated in the rivers and streams of the Rocky Mountains, the eastern side of the Intermountain Region (area between the Sierra Nevada/Cascade Mountains and the Rocky Mountains), and the Sierra Nevada Mountains 13-24. Little is known about the population dynamics of cutthroat trout in lakes across the western US, especially the desert terminal mountain lakes of the Great Bas...

Lakes integrate the signals of changing hydroclimate in their surrounding basin, which substantially influence gross primary production (GPP), respiration (R), and net ecosystem production (NEP). Most research focuses only on the changes to the open water habitat despite the littoral habitat's importance to lakes and its sensitivity to hydroclimatic variability. We analyze how years with different ice‐out dates and snow water equivalent (SWE) triggered different metabolism responses in the open water and littoral habitats of a subalpine lake. The dry (early ice‐out date and low SWE) and wet (late ice‐out date and high SWE) years had lower GPP and R rates in both habitats compared to the average hydroclimatic year. Furthermore, consumer biomass decreased during dry and wet years. GPP and R reduced the most in the littoral habitat. Consequently, the relative contribution to total lake GPP and R of the littoral habitat decreased, and the contribution of the open water habitat increased during the dry and wet years. We demonstrate that hydroclimatic conditions affect productivity and consumer biomass and show that within‐lake habitats do not experience equivalent responses to climate forcing. Our study has implications for how ecosystem scientists and managers quantify the absolute and relative contributions of the littoral habitat to whole lake production in the context of climate variation.