Geology topics

Vanessa R. von Biela

Publications and source records attributed to Vanessa R. von Biela.

At least 19 recordsLinked to original sources

USGS2026

Transcriptional changes in wild Yukon River Chinook Salmon associated with Ichthyophonus infections

Objective We compared differentially expressed genes in Chinook Salmon Oncorhynchus tshawytscha with three divergent Ichthyophonus statuses (undetected, subclinical infections, or clinical disease; n = 100) to investigate associated transcriptomic responses. Disease associated with the fish parasite Ichthyophonus sp. was first diagnosed in adult Chinook Salmon from the Yukon River in the late 1980s and has subsequently been implicated in premature host mortality. Methods Chinook Salmon tissue sample collections and Ichthyophonus infection data were leveraged from a multi-agency collaboration during summer 2022 at three locations along the main-stem Yukon River that spanned nearly 2,000 km of freshwater migration (lower, middle, and upper river). We sequenced the transcriptome and compared this to infection status based on routine diagnostic procedures. Results Among the 17,569 genes for which messenger RNA was detected, we identified a transcription signature in the skeletal muscle that was associated with Ichthyophonus infections and included 53 differentially expressed genes. The differentially expressed genes and their pathways included those known for involvement in immune functions, energy synthesis, cellular breakdown, and reproduction—all processes that are known to be influenced by senescence during spawning migrations. Conclusions Results demonstrate a clear transcriptional difference between diseased fish (clinical disease group) and those in which Ichthyophonus was undetected, including identifying candidate markers for infection in this population. These results provide a foundation for development of nonlethal biomarkers to evaluate potential Ichthyophonus infections in Chinook Salmon based on gene transcription, protein products, or gene variants (e.g., polymorphisms).

Journal of Aquatic Animal Health↗

USGS2026

Indicators of mercury concentration in Lake Trout: Can fish location and appearance provide information to anglers to reduce their exposure?

Objective People are exposed to mercury (Hg) through the consumption of fish. State and federal governments provide broad, often-generalized food safety guidance to reduce exposure; however, numerous rural fishing areas lack testing and location- or species-specific guidance. The aim of this study was to provide tangible, visible, or easily measured characteristics of Lake Trout Salvelinus namaycush that could convey information on Hg exposure to people harvesting and consuming fish where no location-specific guidance exists. Methods We investigated potential indicators of Lake Trout total Hg (THg) concentrations in muscle across 10 lakes in Alaska's national parks. Potential indicators, including lake, lake zone (i.e., littoral, pelagic, profundal), fish length, head size, body condition, and general appearance, were evaluated by competing linear mixed-effects models. Results Lake Trout THg concentrations ranged widely from 22 to 1,306 ng/g wet weight. Much of the variation (48%) in THg concentrations was attributed to differences among individual lakes, but the interaction of the fish's lake zone, body length, and head size accounted for an additional 21%. Predicted THg concentrations increased with Lake Trout length and head : body proportion, but the rate of THg concentration increase with length varied by head : body proportion and lake zone. Conclusions Given the overwhelming evidence of high lake-to-lake variability in Lake Trout THg concentrations, we find support for use of lake-specific guidance when data are available. When lake-specific THg concentrations are not available, the best potential way to reduce exposure is to harvest and consume Lake Trout with mean predicted THg concentrations that are within state and federal safe consumption guidelines. This included Lake Trout from surface waters (i.e., pelagic or littoral zone) that are ≤70 cm in length; if harvesting fish from deep waters (i.e., profundal zone), lower THg concentrations were found in Lake Trout with heads ≤25% of their body length. The indicators—lake zone, length, and head size—of Lake Trout THg concentrations can provide harvesters with additional information in the absence of data for specific lakes.

Alaska↗

USGS2026

Migration water temperature and heat stress assessments in western Alaska Chinook salmon overlapping the 2019 heatwave

Chinook salmon population declines span their geographic range with climate hypothesized as a major driver. Concerns of warming freshwater temperatures in their northern range gained urgency during 2019 when a heatwave coincided with premature mortality. This study examined heat stress during the 2019 heatwave compared to subsequent years and described water temperatures in western Alaska to understand the degree to which freshwater temperatures may be a stressor. Heat stress was prevalent among Chinook salmon captured in the 2019 heatwave (Kuskokwim tributaries: 90% in Kwethluk and 63% Takotna river), and variable in subsequent years (∼8% to 60% across Kuskokwim tributaries and Norton Sound rivers). A review of water temperature data indicated that potentially stressful temperatures (≥18 °C) were most common and prolonged in the Yukon River, moderately common and prolonged in the Kuskokwim River, and relatively rare in the Norton Sound region. Water temperatures in 2019 broke several records for overall maximum and frequency of temperatures ≥ 18 °C. Migration water temperatures and heat stress in northern Pacific salmon habitats vary more widely than previously recognized (up to 25 °C).

Alaska↗

USGS2026

Integrating climate data and river modeling to reveal Chinook salmon habitat conditions in subarctic river basins

Climatic extremes can impact the productivity of aquatic species, affecting ecosystems and fishery-dependent communities. Advances in climate products, such as gridded datasets and downscaled projections, may be useful for quantifying freshwater habitat conditions and predicting climate change effects on fish. However, limited guidance exists for selecting climate products to develop indicators of freshwater habitat conditions that influence fish population dynamics. Here, we develop an approach for identifying streamflow and stream temperature models to address this need. We evaluated skill in predicted versus observed streamflow and stream temperature, with predictions depending on different models and gridded climate data as inputs. The best performing models were used in a case study exploring habitat conditions influencing Chinook salmon in the Yukon and Kuskokwim River basins, two remote high-latitude watersheds with few in situ habitat observations and recent salmon declines. Three modeled streamflow datasets had variable performance (median Nash–Sutcliffe efficiencies from 0.39 to 0.70). Three gridded temperature products differed in their ability to explain variation in weekly stream temperatures (median r 2 from 0.42 to 0.76). We selected a single gridded air temperature dataset to compare two novel predictive stream temperature models, both of which had good accuracy (root mean squared error [RMSE] of 1.19 and 0.95°C). Stream temperature indicators calculated from modeled daily data, maximum temperatures during adult migration and cumulative temperatures during juvenile rearing, had high spatial correlation across tributaries within the Yukon and Kuskokwim River basins and showed significant warming over the past 40 years. Streamflow indicators calculated from modeled daily data, maximum flow during spawning and median flow during rearing, had few trends and were largely uncorrelated within the Yukon River basin and moderately correlated within the Kuskokwim River basin. Overall, we found that generic measures of model performance varied considerably, and it was important to consider the models best suited to our case study. For both streamflow and stream temperature, multiple high-performing models allowed estimation of ecologically relevant conditions affecting Chinook salmon. The approach we used to estimate local-scale habitat conditions has value to identify synchronous conditions that may influence multiple salmon populations under a changing subarctic climate.

Alaska↗

USGS2026

Biomarkers of mortality risks in Yukon Chinook salmon

Premature mortality of spawning adult Pacific salmon ( Oncorhynchus species) can strongly influence population dynamics and complicate escapement-based management. Heat stress and Ichthyophonus infections have been identified as probable drivers of premature mortality in Yukon River Chinook salmon ( Oncorhynchus tshawytscha ) and likely contributors to low spawning abundance. We leveraged a multiagency study focused on Ichthyophonus using lethally collected heart tissue as a rare opportunity to investigate these two stressors jointly in the same individuals to accomplish two tasks: (1) provide a more comprehensive premature mortality risk index that combines heat stress and Ichthyophonus detection and (2) investigate the feasibility of using skeletal muscle tissue gene transcription (mRNA of select genes) as a non-lethal biomarker of Ichthyophonus . Water temperatures ranged from ~12–22°C across four sites and two years. In both 2023 and 2024, effects were identified in ~30% of salmon at Pilot Station, Alaska, and ~70% of salmon by the time they reached mid river (Rapids, Fort Yukon). Mortality risk is presumably highest among fish with multiple stressors, which were detected in ~25% of Chinook salmon in the middle river sites in 2023 when it was warmer and 9—18% in 2024 when it was cooler. We explored Chinook salmon genes that respond to Ichthyophonus with a full transcriptome analysis that measured mRNA of 17,569 genes and identified 53 that were related to Ichthyophonus infection. The differentially expressed genes and their pathways included those known for involvement in immune functions, energy synthesis, cellular breakdown, and reproduction– all processes known to be influenced by senescence during spawning migrations and imply accelerated senescence of infected fish. Primers were developed for 21 of the differentially expressed Chinook salmon genes for qPCR measurements of their mRNA that could be used in classification models. Attempts to statistically deduce Ichthyophonus infection from Chinook salmon gene transcription at the individual and group levels included some potential for separating fish where Ichthyophonus was not detected compared to those with high infection intensities (as judged by qPCR that directly detects Ichthyophonus DNA). Fish with relatively low infection intensities did not have a separate gene transcription signature and grouped with the undetected Ichthyophonus fish in two-thirds of the cases and high infection in onethird of cases. Among the genes with the most utility to predict Ichthyophonus infection were retinoic acid receptor beta (regulates cellular states) and lysozyme CII (immune system gene). Interannual variation in the gene transcription of fish with undetected Ichthyophonus was a complicating factor that demonstrated a need for additional refinement and testing. Overall, this study identified two broad findings: (1) The proportion of migrating fish with one or both of the assessed stressors ( Ichthyophonus infections and/or elevated levels of heat shock protein) can be very high (~70%) and (2) we recommend measuring interannual variation of gene transcription in any study that seeks to develop gene transcription as a biomarker.

Alaska↗

USGS2025

Energetic value of Arctic forage-sized fish with implications for a nearshore seabird predator

Arctic cod ( Boreogadus saida , also called polar cod) are considered the single most important Arctic forage fish due to their high abundance and nutritional quality. Because Arctic cod are strongly ice associated and prefer colder waters, their frequency in coastal waters has declined with warming, decreasing availability to nearshore predators. To consider the nutritional quality of alternative prey, we measured energy density and estimated whole-body energy of forage-size (39–200 mm) fishes collected during summers 2021–2023 ( n = 274). The fishes sampled included 16 potential prey species from Foggy Island Bay (70.3°N, 147.5°W, near Prudhoe Bay) and Lion Bay (70.2°N, 146.4°W, near Flaxman Island), northern Alaska. Dry weight energy densities ranged from 16.2 to 27.5 kJ g -1 (mean ± SD = 22.0 ± 1.73 kJ g -1 , n = 274) across individuals. Of common species, Arctic cod had the highest mean energy density (24.3 ± 1.1 kJ g -1 , n = 25) and fourhorn sculpin ( Myoxocephalus quadricornis ) had the lowest (19.7 ± 0.8 kJ g -1 , n = 20). To account for size differences among prey species, whole-body energy of typical fish sizes available to predators were modeled using whole-body energy to length relationships and length distributions. Juvenile salmonids (e.g., ciscoes and whitefishes) provided the most energy per individual and were four-fold greater than smaller-bodied Arctic cod. Predators that consume juvenile ciscoes and whitefishes may be more resilient to declines in Arctic cod availability than predators with smaller gapes.

Alaska↗

USGS2024

Body size and early marine conditions drive changes in Chinook salmon productivity across northern latitude ecosystems

Disentangling the influences of climate change from other stressors affecting the population dynamics of aquatic species is particularly pressing for northern latitude ecosystems, where climate-driven warming is occurring faster than the global average. Chinook salmon ( Oncorhynchus tshawytscha ) in the Yukon-Kuskokwim (YK) region occupy the northern extent of their species' range and are experiencing prolonged declines in abundance resulting in fisheries closures and impacts to the well-being of Indigenous people and local communities. These declines have been associated with physical (e.g., temperature, streamflow) and biological (e.g., body size, competition) conditions, but uncertainty remains about the relative influence of these drivers on productivity across populations and how salmon–environment relationships vary across watersheds. To fill these knowledge gaps, we estimated the effects of marine and freshwater environmental indicators, body size, and indices of competition, on the productivity (adult returns-per-spawner) of 26 Chinook salmon populations in the YK region using a Bayesian hierarchical stock-recruitment model. Across most populations, productivity declined with smaller spawner body size and sea surface temperatures that were colder in the winter and warmer in the summer during the first year at sea. Decreased productivity was also associated with above average fall maximum daily streamflow, increased sea ice cover prior to juvenile outmigration, and abundance of marine competitors, but the strength of these effects varied among populations. Maximum daily stream temperature during spawning migration had a nonlinear relationship with productivity, with reduced productivity in years when temperatures exceeded thresholds in main stem rivers. These results demonstrate for the first time that well-documented declines in body size of YK Chinook salmon were associated with declining population productivity, while taking climate into account.

Global Change Biology↗

USGS2024

Arctic fishes reveal patterns in radiocarbon age across habitats and with recent climate change

Climate change alters the sources and age of carbon in Arctic food webs by fostering the release of older carbon from degrading permafrost. Radiocarbon ( 14 C) traces carbon sources and age, but data before rapid warming are rare and limit assessments over time. We capitalized on 14 C data collected ~ 40 years ago that used fish as natural samplers by resampling the same species today. Among resampled fish, those using freshwater food webs had the oldest 14 C ages (> 1000 yr BP), while those using marine food webs had the youngest 14 C ages (near modern). One migratory species encompassed the entire range of 14 C ages because juveniles fed in freshwater streams and adults fed in offshore marine habitats. Over ~ 40 yr, average 14 C ages of freshwater and marine feeding fish shifted closer to atmospheric values, suggesting a potential influence from “greening of the Arctic.”

Alaska↗

USGS2024

Relative importance of macroalgae and phytoplankton to nearshore consumers and growth across climatic conditions in the northern Gulf of Alaska

Macroalgae and phytoplankton support the base of highly productive nearshore ecosystems in cold-temperate regions. To better understand their relative importance to nearshore food webs, this study considered four regions in the northern Gulf of Alaska where three indicator consumers were collected, filter-feeding mussels ( Mytilus trossulus ), pelagic-feeding Black Rockfish ( Sebastes melanops ), and benthic-feeding Kelp Greenling ( Hexagrammos decagrammus ). The study objectives were to (1) estimate the proportional contributions of macroalgal and phytoplankton organic matter using carbon and nitrogen stable isotopes, (2) determine if macroalgal use affected consumer growth using annual growth rings in shells or otoliths, and (3) describe changes in organic matter use and growth during the Pacific Marine Heatwave (PMH; 2014–2016) in one consumer, mussels. Macroalgae were the major organic matter source (> 60%) to the diet for all three consumers. The relationships between macroalgal contribution and growth were neutral for both fish species and significantly positive for mussels. During the PMH, mussels had a drop (> 10%) in macroalgal contributions and grew 45% less than in other time periods. Simultaneously, the relationship between macroalgal contribution and mussel growth was strongest during the PMH, explaining 48% variation compared to 3–12% before or after the PMH. Collectively, the results suggest that macroalgae is likely more important to cold-temperate nearshore food webs than phytoplankton. Management actions aimed at conserving and expanding macroalgae are likely to benefit nearshore food webs under all climate scenarios and especially during marine heatwaves.

Alaska↗

USGS2024

Reduction in overwinter body condition and size of Pacific sand lance has implications for piscivorous predators during marine heatwaves

Acute anomalous ocean warming events, including marine heatwaves (MHWs), have significant effects on reproduction and survival of piscivorous seabirds. Additionally, MHWs have negative effects on seabird fish prey, exacerbating these consequences and resulting in population implications for seabirds. We evaluated the relative body condition of Pacific sand lance Ammodytes personatus , an important seabird forage species, in Haro Strait, a highly productive region of southern British Columbia, Canada. We compared body condition and length of fish cohorts that experienced the 2016 MHW year (MHW cohorts) with fish hatched during 3 subsequent post MHW years (2017-2019). Age-0 MHW cohorts had a seasonal decline in body condition in age-0 fish from 100% in the summer to 81% in the winter, while age-1 fish showed a decline from summer-fall highs of 93.5% to wintertime low of 79.5%. In comparison, post MHW cohorts had a winter body condition that was 2-4 times higher than their MHW cohorts. Similar to previous studies in Alaska during the MHW, age-1 fish failed to grow and reach the typical size that distinguishes them from age-0 fish. Poor sand lance condition and growth in winter may explain the ramifications of a warming ocean for top predators, including seabirds and Pacific salmon, which depend on these prey fish in Haro Strait. Our results support the idea that Haro Strait, which is influenced by estuarine circulation resulting in cooler temperatures than surrounding areas, serves as a climate refugium for sand lance populations in summer and provides buffering capacity to ocean climate warming events.

Marine Ecology Progress Series↗

USGS2024

Local environmental conditions structured discrete fish assemblages in Arctic lagoons

Rapid changes in sea ice extent and changes in freshwater inputs from land are rapidly changing the nature of Arctic estuarine ecosystems. In the Beaufort Sea, these nearshore habitats are known for their high productivity and mix of marine resident and diadromous fishes that have great subsistence value for Indigenous communities. There is, however, a lack of information on the spatial variation among Arctic nearshore fish communities as related to environmental drivers. In summers of 2017–2019, we sampled fishes in four estuarine ecosystems to assess community composition and relate fish abundance to temperature, salinity, and wind conditions. We found fish communities were heterogeneous over larger spatial extents with rivers forming fresh estuarine plumes that supported diadromous species (e.g., broad whitefish Coregonus nasus ), while lagoons with reduced freshwater input and higher salinities were associated with marine species (e.g., saffron cod Eleginus gracilis ). West–East directional winds accounted for up to 66% of the community variation, indicating importance of the wind-driven balance between fresh and marine water masses. Salinity and temperature accounted for up to 54% and 37% of the variation among lagoon communities, respectively. Recent sea ice declines provide more opportunity for wind to influence oceanographic conditions and biological communities. Current subsistence practices, future commercial fishing opportunities, and on-going oil and gas activities benefit from a better understanding of current fish community distributions. This work provides important data on fish spatial distributions and community composition, providing a basis for fish community response to changing climatic conditions and anthropogenic use.

Polar Biology↗

USGS2024

Does the extent of glacial cover across watersheds and discharge periods affect dietary resource use of nearshore fishes in the Northern Gulf of Alaska?

Northern high-latitude glaciers impact nearshore marine ecosystems through the discharge of cold and fresh waters, including nutrients and organic matter. Fishes are important integrators of ecosystem processes and hold key positions in the transfer of energy to higher trophic positions in such systems. This study used a natural gradient in space and time, including watershed glacial cover (0–60%) of five adjacent estuaries and three sequential discharge periods (pre-peak, peak, post-peak) in the northern Gulf of Alaska (Kachemak Bay) to test whether differences in glacial cover of watersheds upstream of estuaries affect dietary resource use of nearshore fishes. Dietary resource use was assessed using stomach content and stable carbon and nitrogen isotope analyses to determine fish diet composition and trophic niche width. Crescent gunnel ( Pholis laeta ), a mostly sedentary species, was our focal species for comparisons across estuaries and discharge periods. Discharge period had a greater influence on diet composition and trophic niche width of crescent gunnels than watershed glacial coverage. Niche width of crescent gunnel was larger during the post-peak discharge period compared to pre-peak and peak periods, coincident with a shift in prey spectrum. However, watershed glacial cover was not a suitable predictor of niche width of crescent gunnel. Trophic resource use was also considered along this glacial cover gradient for two other fish species, Pacific staghorn sculpin ( Leptocottus armatus ) and starry flounder ( Platichthys stellatus ), but within the post-peak discharge period only. These species exploited a larger prey base compared to crescent gunnel, likely due to their greater mobility. Similar to crescent gunnel, there were no relationships in trophic niche width associated with watershed glacial coverage for these other species during the post-peak discharge period. Instead, trophic resource use of these three nearshore fish species was influenced by a more complex set of dynamic environmental variables (salinity, temperature, turbidity, and discharge), as well as static watershed characteristics, especially vegetation cover. Such drivers can act through changes in metabolic rates, modulating foraging strategies and trophic connectivity, as well as terrestrial nutrient delivery to support estuarine production. The environmental conditions associated with the glacially influenced estuaries during our study period (2020−2021) seemed within a range that allowed nearshore fishes to maintain energy pathways and prey bases across these estuaries, but it is unknown how these estuarine food webs may be influenced in years of extreme conditions such as during heat waves, droughts, or floods.

Alaska↗

USGS2023

Differential heat shock protein responses in two species of Pacific salmon and their utility in identifying heat stress

Rapid and accelerating warming of salmon habitat has the potential to lower productivity of Pacific salmon ( Oncorhynchus species) populations. Heat stress biomarkers can indicate where warming is most likely affecting fish populations; however, we often lack clear classifications that separate individuals with and without heat stress needed to make these tools operational. We conducted a heat exposure experiment with trials lasting 12 or 36 h using juvenile Chinook salmon ( Oncorhynchus tshawytscha ) and coho salmon ( Oncorhynchus kisutch ) to validate heat stress biomarkers in white muscle. Following habituation to 13°C, individuals were exposed to water temperatures that increased to 15°C, 17°C, 19°C, 21°C or 23°C. Heat shock protein 70 abundance (HSP70 measured by ELISA) and transcription of 13 genes (mRNA measured by qPCR) including three heat shock protein genes ( hsp70, hsp90, hsp27 ) were measured. A distinct heat stress response was apparent by 21°C in juvenile Chinook salmon and 23°C in juvenile coho salmon using HSP70. A threshold for heat stress classification in Chinook salmon of > 2 ng HSP70 mg .1 total protein identified heat stress in 100% of 21 and 23°C treated individuals compared to 4% in cooler treatments. For coho salmon, > 3 ng HSP70 mg .1 total protein identified heat stress in 100% of 23°C treated individuals compared to 4% in cooler treatments. Transcription from a panel of genes separated individuals between cooler and stressful temperature experiences (≥21°C for Chinook salmon and ≥23°C for coho salmon) with ~ 85% correct classification. Our findings indicate that juvenile Chinook salmon were more temperature-sensitive than juvenile coho salmon and support the use of a HSP70 threshold sampled from muscle for assessing heat stress in individual wild Pacific salmon with an option for non-lethal biopsies for spawning adults.

Conservation Physiology↗

USGS2023

Kings of the North: Bridging disciplines to understand the effects of changing climate on Chinook salmon in the Arctic-Yukon-Kuskokwim Region

Understanding how species are responding to environmental change is a central challenge for stewards and managers of fish and wildlife who seek to maintain harvest opportunities for communities and Indigenous peoples. This is a particularly daunting but increasingly important task in remote, high-latitude regions where environmental conditions are changing rapidly and data collection is logistically difficult. The Arctic-Yukon-Kuskokwim (AYK) region encompasses the northern extent of the Chinook Salmon Oncorhynchus tshawytscha range where populations are experiencing rapid rates of environmental change across both freshwater and marine habitats due to global climate change. Climate–salmon interactions in the AYK region are a particularly pressing issue as many local communities have a deep reliance on a subsistence way of life. Here, we synthesize perspectives shared at a recent workshop on Chinook Salmon declines in the AYK region. The objectives were to discuss current understandings of climate-Chinook Salmon interactions, develop a set of outstanding questions, review available data and its limitations in addressing these questions, and describe the perspectives expressed by participants in this workshop from diverse backgrounds. We conclude by suggesting pathways forward to integrate different types of information and build relationships among communities, academic partners, and fishery management agencies.

Alaska, British Columbia, Yukon↗

USGS2023

Adult spawners: A critical period for subarctic Chinook salmon in a changing climate

Concurrent, distribution-wide abundance declines of some Pacific salmon species, including Chinook salmon ( Oncorhynchus tshawytscha ), highlights the need to understand how vulnerability at different life stages to climate stressors affects population dynamics and fisheries sustainability. Yukon River Chinook salmon stocks are among the largest subarctic populations, near the northernmost extent of the species range. Existing research suggests that Yukon River Chinook salmon population dynamics are largely driven by factors occurring between the adult spawner life stage and their offspring's first summer at sea (second year post-hatching). However, specific mechanisms sustaining chronic poor productivity are unknown, and there is a tremendous sense of urgency to understand causes, as declines of these stocks have taken a serious toll on commercial, recreational, and indigenous subsistence fisheries. Therefore, we leveraged multiple existing datasets spanning parent and juvenile stages of life history in freshwater and marine habitats. We analyzed environmental data in association with the production of offspring that survive to the marine juvenile stage (juveniles per spawner). These analyses suggest more than 45% of the variability in the production of juvenile Chinook salmon is associated with river temperatures or water discharge levels during the parent spawning migration. Over the past two decades, parents that experienced warmer water temperatures and lower discharge in the mainstem Yukon River produced fewer juveniles per spawning adult. We propose the adult spawner life stage as a critical period regulating population dynamics. We also propose a conceptual model that can explain associations between population dynamics and climate stressors using independent data focused on marine nutrition and freshwater heat stress. It is sobering to consider that some of the northernmost Pacific salmon habitats may already be unfavorable to these cold-water species. Our findings have immediate implications, given the common assumption that northern ranges of Pacific salmon offer refugia from climate stressors.

Alaska↗

USGS2023

Borealization of nearshore fishes on an interior Arctic shelf over multiple decades

Borealization is a type of community reorganization where Arctic specialists are replaced by species with more boreal distributions in response to climatic warming. The process of borealization is often exemplified by the northward range expansions and subsequent proliferation of boreal species on the Pacific and Atlantic inflow Arctic shelves (i.e., Bering/Chukchi and Barents seas, respectively). But the circumpolar nearshore distribution of Arctic-boreal fishes that predates recent warming suggests borealization is possible beyond inflow shelves. To examine this question, we revisited two nearshore lagoons in the eastern Alaska Beaufort Sea (Kaktovik and Jago lagoons, Arctic National Wildlife Refuge, Alaska, USA), a High Arctic interior shelf. We compared summer fish species assemblage, catch rate, and size distribution among three periods that spanned a 30-year record (baseline conditions, 1988–1991; moderate sea ice decline, 2003–2005; rapid sea ice decline, 2017–2019). Fish assemblages differed among periods in both lagoons, consistent with borealization. Among Arctic specialists, a clear decline in fourhorn sculpin ( Myoxocephalus quadricornis , Kanayuq in Iñupiaq) occurred in both lagoons with 86%–90% lower catch rates compared with the baseline period. Among the Arctic-boreal species, a dramatic 18- to 19-fold increase in saffron cod ( Eleginus gracilis , Uugaq) occurred in both lagoons. Fish size (length) distributions demonstrated increases in the proportion of larger fish for most species examined, consistent with increasing survival and addition of age-classes. These field data illustrate borealization of an Arctic nearshore fish community during a period of rapid warming. Our results agree with predictions that Arctic-boreal fishes (e.g., saffron cod) are well positioned to exploit the changing Arctic ecosystem. Another Arctic-boreal species, Dolly Varden ( Salvelinus malma , Iqalukpik), appear to have already responded to warming by shifting from Arctic nearshore to shelf waters. More broadly, our findings suggest that areas of borealization could be widespread in the circumpolar nearshore.

Alaska↗

USGS2023

Divergent responses of western Alaska salmon to a changing climate

Headlines Western Alaska salmon abundance reached historic extremes during 2021-22, with record lows for Chinook and chum salmon (81% and 92% below the 30-year mean, respectively) and record highs for sockeye salmon (98% above the 30-year mean). Salmon are maturing at smaller sizes. Since the 1970s, for example, Yukon River Chinook salmon have decreased an estimated 6% in mean adult body length and 15% in fecundity, likely exacerbating population declines. Salmon population declines have led to fishery closures, worsened user conflicts, and had profound cultural and food security impacts in Indigenous communities that have been tied to salmon for millennia. Changes in abundance and size are associated with climatic changes in freshwater and marine ecosystems and competition in the ocean. Changes in predators, food supply, and disease are also likely important drivers.

Alaska↗

USGS2022

Fish ear stones offer climate change clues in Alaska's lakes

Otoliths, also known as ear stones, are small body parts that help fish with hearing and balance. Like tree rings, otoliths form one light and one dark band per year, creating rings. These rings can be measured to understand fish growth. The wider the ring, the greater the growth. In our study, we used otoliths to understand how one fish species—lake trout—responds to rising temperature in the state of Alaska. We found that warmer spring air temperature and earlier lake ice melt were related to faster lake trout growth. This finding is consistent with other studies that link warmer water temperature and earlier lake ice melt to increased plankton in Alaska’s lakes. Together, these findings suggest that climate-driven increases at the bottom of the food web might benefit top predators like lake trout. However, the relationship between warmer temperature and faster growth may not last.

Alaska↗