The increasing availability of high-resolution digital elevation data is enhancing the mapping of hydrography across Earth’s surface. As pressures on fluvial ecosystems grow, digital maps of river networks should include a data structure necessary to assess aquatic habitats and the environmental threats to them from resource development and climate change. Using examples from across Alaska, USA, we demonstrate how newly available radar and laser digital elevation products are being used to discover thousands of kilometers of previously unmapped channels, ranging from headwater to valley bottom streams. This comprehensive and attributed high-resolution hydrography that connects lentic, lotic, and terrestrial systems—a virtual watershed—has resulted in tens to hundreds of percent increases in potential salmonid habitats across landscapes ranging from the Arctic tundra to southeast rainforests. Our findings show how virtual watersheds enhance understanding of freshwater and diadromous fish habitats and serve as a model for supporting conservation efforts and environmental problem-solving in other regions globally.

Arctic freshwater ecosystems and fish populations are largely shaped by seasonal and long‐term watershed hydrology. In this paper, we hypothesize how changing air temperature and precipitation will alter freeze and thaw processes, hydrology, and instream habitat to assess potential indirect effects, such as the change to the foraging and behavioral ecology, on Arctic fishes, using Broad Whitefish Coregonus nasus as an indicator species. Climate change is expected to continue to alter hydrologic pathways, flow regimes, and, therefore, habitat suitability, connectivity, and availability for fishes. Warming and lengthening of the growing season will likely increase fish growth rates; however, the exceedance of threshold stream temperatures will likely increase physiological stress and alter life histories. We expect these changes to have mixed effects on Arctic subsistence fishes and fisheries. Management and conservation approaches focused on preserving the processes that create heterogeneity in aquatic habitats, genes, and communities will help maintain the resilience of Broad Whitefish and other important subsistence fisheries. Long‐term effects are uncertain, so filling scientific knowledge gaps, such as identifying important habitats or increasing knowledge of abiotic variables in priority watersheds, is key to understanding and potentially mitigating likely impacts to Arctic fishes in a rapidly changing landscape.

Conservation of Arctic fish species is challenging partly due to our limited ability to track fish through time and space, which constrains our understanding of life history diversity and lifelong habitat use. Broad Whitefish ( Coregonus nasus ) is an important subsistence species for Alaska’s Arctic Indigenous communities, yet little is known about life history diversity, migration patterns, and freshwater habitat use. Using laser ablation Sr isotope otolith microchemistry, we analyzed Colville River Broad Whitefish 87 Sr/ 86 Sr chronologies (n = 61) to reconstruct movements and habitat use across the lives of individual fish. We found evidence of at least six life history types, including three anadromous types, one semi-anadromous type, and two nonanadromous types. Anadromous life history types comprised a large proportion of individuals sampled (collectively, 59%) and most of these (59%) migrated to sea between ages 0–2 and spent varying durations at sea. The semi-anadromous life history type comprised 28% of samples and entered marine habitat as larvae. Nonanadromous life history types comprised the remainder (collectively, 13%). Otolith 87 Sr/ 86 Sr data from juvenile and adult freshwater stages suggest that habitat use changed in association with age, seasons, and life history strategies. This information on Broad Whitefish life histories and habitat use across time and space will help managers and conservation planners better understand the risks of anthropogenic impacts and help conserve this vital subsistence resource.

Landscape-level geomorphic processes influence the spatial and temporal arrangement of fish habitats in freshwater ecosystems and fishes move across riverscapes, selecting a suite of habitats to maximise fitness. Here, we explore the influence of geomorphology on stream channel attributes and assess Broad Whitefish (Coregonus nasus) spawning habitat potential in the Colville River in Arctic Alaska. Using high-resolution digital surface models (5 m(2)), we quantified the stream network extent and summarised channel habitat attributes continuously across the drainage network. Next, we developed an intrinsic potential (IP) model for Broad Whitefish by using geomorphic channel parameters previously understood to be associated with spawning habitats (channel width, median substrate size and channel braiding) to estimate the potential of streams across the Colville River watershed to provide spawning habitat. Our model results show the majority of habitat with high IP (>= 0.6) was located within the braided sections of the main channel, which encompass >1548 km, but only 2% of the total channel network. The IP model was tested by tracking radio-tagged Broad Whitefish using aerial surveys. Prespawn fish moved into the watershed starting mid-July and mostly used habitat with moderate to very high IP in the middle and lower watershed. Several individuals were relocated in smaller multichannels with vegetated bars that contained very low IP (<= 0.2), suggesting that other factors, such as hyporheic flow, may also influence spawning habitat selection. Our study demonstrates that IP modelling offers a useful method to quantify spawning habitat potential in data-poor riverscapes, providing useful information for managers to assess potential anthropogenic impacts and develop conservation plans to protect essential Broad Whitefish habitat.

Understanding the ecological niche of some fishes is complicated by their frequent use of a broad range of food resources and habitats across space and time. Little is known about Broad Whitefish ( Coregonus nasus ) ecological niches in Arctic landscapes even though they are an important subsistence species for Alaska’s Indigenous communities. We investigated the foraging ecology and habitat use of Broad Whitefish via stable isotope analyses of muscle and liver tissue and otoliths from mature fish migrating in the Colville River within Arctic Alaska. The range of δ 13 C (-31.8– -21.9‰) and δ 15 N (6.6–13.1‰) across tissue types and among individuals overlapped with isotope values previously observed in Arctic lakes and rivers, estuaries, and nearshore marine habitat. The large range of δ 18 O (4.5–10.9‰) and δD (-237.6– -158.9‰) suggests fish utilized a broad spectrum of habitats across elevational and latitudinal gradients. Cluster analysis of muscle δ 13 Cˈ, δ 15 N, δ 18 O, and δD indicated that Broad Whitefish occupied four different foraging niches that relied on marine and land-based (i.e., freshwater and terrestrial) food sources to varying degrees. Most individuals had isotopic signatures representative of coastal freshwater habitat (Group 3; 25%) or coastal lagoon and delta habitat (Group 1; 57%), while individuals that mainly utilized inland freshwater (Group 4; 4%) and nearshore marine habitats (Group 2; 14%) represented smaller proportions. Otolith microchemistry confirmed that individuals with more enriched muscle tissue δ 13 Cˈ, δD, and δ 18 O tended to use marine habitats, while individuals that mainly used freshwater habitats had values that were less enriched. The isotopic niches identified here represent important foraging habitats utilized by Broad Whitefish. To preserve access to these diverse habitats it will be important to limit barriers along nearshore areas and reduce impacts like roads and climate change on natural flow regimes. Maintaining these diverse connected habitats will facilitate long-term population stability, buffering populations from future environmental and anthropogenic perturbations.

Current systems of conservation reserves may be insufficient to sustain biodiversity in the face of climate change and habitat losses. Consequently, calls have been made to protect Earth's remaining wildlands and complete the system of protected areas by establishing conservation reserves that (1) better represent ecosystems, (2) increase connectivity to facilitate biota movement in response to stressors including climate change, and (3) promote species persistence within intact landscapes. Using geospatial data, we conducted an assessment for expanding protected areas within the contiguous United States to include the least human-modified wildlands, establish a connected network, and better represent ecosystem diversity and hotspots of biodiversity. Our composite map highlights areas of high value to achieve these goals in the western United States, where existing protected areas and lands with high ecological integrity are concentrated. We also identified important areas in the East rich in species and containing ecosystems that are poorly represented in the existing protected area system. Expanding protection to these priority areas is ultimately expected to create a more resilient system for protecting the nation's biological heritage. This expectation should be subject to rigorous testing prior to implementation, and regional monitoring will ensure areas and actions are adjusted over time.

FisheriesVolume 42, Issue 6 p. 315-319 Column: Cool Fish In Search of Arctic Bonefish Jason Leppi, Jason Leppi jcleppi@alaska.edu Alaska Cooperative Fish and Wildlife Research Unit, College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK The Wilderness Society, Anchorage, AKSearch for more papers by this authorMichael Lunde, Michael Lunde Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AKSearch for more papers by this authorMark Wipfli, Mark Wipfli U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AKSearch for more papers by this authorDan Rinella, Dan Rinella U.S. Fish and Wildlife Service, Anchorage Fish and Wildlife Conservation Office, Anchorage, AKSearch for more papers by this author Jason Leppi, Jason Leppi jcleppi@alaska.edu Alaska Cooperative Fish and Wildlife Research Unit, College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK The Wilderness Society, Anchorage, AKSearch for more papers by this authorMichael Lunde, Michael Lunde Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AKSearch for more papers by this authorMark Wipfli, Mark Wipfli U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AKSearch for more papers by this authorDan Rinella, Dan Rinella U.S. Fish and Wildlife Service, Anchorage Fish and Wildlife Conservation Office, Anchorage, AKSearch for more papers by this author First published: 30 May 2017 https://doi.org/10.1080/03632415.2017.1323525Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume42, Issue6June 2017Pages 315-319 RelatedInformation

Climate is changing fastest in high-latitude regions, focusing our research on understanding rates and drivers of changing temperature regimes in southcentral Alaska streams and implications for salmon populations. We collected continuous water and air temperature data during open-water periods from 2008 to 2012 in 48 nonglacial salmon streams across the Cook Inlet basin spanning a range of watershed characteristics. The most important predictors of maximum temperatures, expressed as mean July temperature, maximum weekly average temperature, and maximum weekly maximum temperature (MWMT), were mean elevation and wetland cover, while thermal sensitivity (slope of the stream–air temperature relationship) was best explained by mean elevation and area. Although maximum stream temperatures varied widely between years and across sites (8.4 to 23.7 °C), MWMT at most sites exceeded established criterion for spawning and incubation (13 °C), above which chronic and sublethal effects become likely, every year of the study, which suggests salmon are already experiencing thermal stress. Projections of MWMT over the next ∼50 years suggest these criteria will be exceeded at more sites and by increasing margins.

We report the first confirmed cases (2013–2016) of saprolegniosis caused by water mold from the genus Saprolegnia in Aanaakłiq, broad whitefish (Coregonus nasus), from the Colville River near Nuiqsut, Alaska. While this mold is known to be worldwide, these instances represent the first cases in Nuiqsut and only the second instance on a single fish on the North Slope, occurring in 1980. We describe the collaborative work on monitoring this emerging disease. Because fish constitute a critical component of the diet in Nuiqsut and fishing is an integral part of Inupiaq nutritional and cultural subsistence activities overall, individual subsistence fishers, local governmental entities, and Alaska Native organizations representing Nuiqsut requested an examination of affected fish and information on possible drivers of this emerging disease. The collaborative work described here ranges from recording fishermen observations, acquiring fish and mold specimens, histopathology, and molecular identification of the mold. This work, not currently grant-funded, begins with Native observation that incorporates western scientific methods and involves local, state, and federal departments as well as for-profit and non-profit organizations. Additionally, we report the more recent (2016) observation of this disease in a second species of whitefish, Pikuktuuq, humpback whitefish (Coregonus pidschain).

Overwintering habitat for Arctic freshwater fish is essential, such that understanding the distribution of winter habitat quality at the landscape-scale is warranted. Adequate dissolved oxygen (DO) is a major factor limiting habitat quality in the Arctic region where ice cover can persist for 8 months each year. Here we use a mixed-effect model developed from 20 lakes across northern Alaska to assess which morphology and landscape attributes can be used to predict regional overwintering habitat quality. Across all lakes, we found that the majority of the variations in late winter DO can be explained by lake depth and littoral area. In shallow lakes (<4 m), we found evidence that additional variables such as elevation, lake area, ice cover duration, and snow depth were associated with DO regimes. Low DO regimes were most typical of shallow lakes with large littoral areas and lakes that had high DO regimes often were lakes with limited littoral areas and deeper water. Our analysis identifies metrics that relate to late winter DO regimes in Arctic lakes that can aid managers in understanding which lakes will likely provide optimum DO for overwintering habitat. Conversely, lakes which predicted to have marginal winter DO levels may be vulnerable to disturbances that could lower DO below critical thresholds to support sensitive fish. In regions where lakes are also used by humans for industrial winter water supply, such as ice-road construction for oil and gas development, these findings will be vital for the management of resources and protection of Arctic fish.

Climate change is predicted to dramatically change hydrologic processes across Alaska, but estimates of how these impacts will influence specific watersheds and aquatic species are lacking. Here, we linked climate, hydrology, and habitat models within a coho salmon (Oncorhynchus kisutch) population model to assess how projected climate change could affect survival at each freshwater life stage and, in turn, production of coho salmon smolts in three subwatersheds of the Chuitna (Chuit) River watershed, Alaska. Based on future climate scenarios and projections from a three-dimensional hydrology model, we simulated coho smolt production over a 20-year span at the end of the century (2080-2100). The direction (i.e., positive vs. negative) and magnitude of changes in smolt production varied substantially by climate scenario and subwatershed. Projected smolt production decreased in all three subwatersheds under the minimum air temperature and maximum precipitation scenario due to elevated peak flows and a resulting 98% reduction in egg-to-fry survival. In contrast, the maximum air temperature and minimum precipitation scenario led to an increase in smolt production in all three subwatersheds through an increase in fry survival. Other climate change scenarios led to mixed responses, with projected smolt production increasing and decreasing in different subwatersheds. Our analysis highlights the complexity inherent in predicting climate-change-related impacts to salmon populations and demonstrates that population effects may depend on interactions between the relative magnitude of hydrologic and thermal changes and their interactions with features of the local habitat.

In the snowmelt dominated hydrology of arid western US landscapes, late summer low streamflow is the most vulnerable period for aquatic ecosystem habitats and trout populations. This study analyzes mean August discharge at 153 streams throughout the Central Rocky Mountains of North America (CRMs) for changes in discharge from 1950–2008. The purpose of this study was to determine if: (1) Mean August stream discharge values have decreased over the last half-century; (2) Low discharge values are occurring more frequently; (3) Climatic variables are influencing August discharge trends. Here we use a strict selection process to characterize gauging stations based on amount of anthropogenic impact in order to identify heavily impacted rivers and understand the relationship between climatic variables and discharge trends. Using historic United States Geologic Survey discharge data, we analyzed data for trends of 40–59 years. Combining of these records along with aerial photos and water rights records we selected gauging stations based on the length and continuity of discharge records and categorized each based on the amount of diversion. Variables that could potentially influence discharge such as change in vegetation and Pacific Decadal Oscillation (PDO) were examined, but we found that that both did not significantly influence August discharge patterns. Our analyses indicate that non-regulated watersheds are experiencing substantial declines in stream discharge and we have found that 89% of all non-regulated stations exhibit a declining slope. Additionally our results here indicate a significant (α ≤ 0.10) decline in discharge from 1951–2008 for the CRMs. Correlations results at our pristine sites show a negative relationship between air temperatures and discharge and these results coupled with increasing air temperature trends pose serious concern for aquatic ecosystems in CRMs.

August is a critical time for aquatic ecosystems in the Northern Rockies (NR) region due to the characteristics of the snowmelt dominated watersheds and the regional climate. To date there has been limited effort to evaluate August stream discharge trends in the NR. Discharge rates directly affect in-stream temperature, health and function of aquatic ecosystems during summer months. The purpose of this study was to determine if mean August stream discharge values have decreased over the last half-century and if low discharge values are occurring more frequently. Using historic discharge data from United States Geologic Survey’s national water information system web interface, we analyzed data for trends of 40-59 years. Combining of these records along with aerial photos (with <10m resolution) and water rights records we selected gauging sites based on the length and continuity of discharge records and categorized each site based on the amount of diversion and location of water storage devices. Local significance was examined using the Mann-Kendall non-parametric test and regional significance was obtained using a bootstrap procedure in combination with the Mann-Kendall test. Our analyses indicate that watersheds throughout the NR are experiencing substantial declines in stream discharge and we have found that 75% of all stations exhibit a declining slope. The bootstrap analysis explored here indicates a significant (α ≤ 0.10) decline in discharge from 1951-2008. This regional assessment of stream discharge trends will provide invaluable information for local, county and state conservation plans and help to understand the severity of action needed to address decreasing discharge in the future.