Search for: All records

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 m²), 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.

Lakes can be important to stream dwelling fishes, yet how individuals exploit habitat heterogeneity across complex stream‐lake networks is poorly understood. Furthermore, despite growing awareness that intermittent streams are widely used by fish, studies documenting the use of seasonally accessible lakes remain scarce. We studied Arctic grayling (Thymallus arcticus) in a small seasonally flowing (June–October) stream‐lake network in Alaska using PIT telemetry. Overall, 70% of fish visited two lakes, 8% used a single lake, and 22% used only stream reaches. We identified five distinct behavioural patterns that differed in dominant macrohabitat used (deep lake, shallow lake or stream reaches), entry day into the network and mobility. Some juvenile fish spent the entire summer in a shallow seasonally frozen lake (average 71 days), whereas others demonstrated prospecting behaviour and only entered the stream channel briefly in September. Another group included adult and juvenile fish that were highly mobile, moving up to 27 km while in the 3‐km stream‐lake network, and used stream reaches extensively (average 59 days). Lentic and lotic habitats served differing roles for individuals, some fish occupied stream reaches as summer foraging habitat, and other individuals used them as migration corridors to access lakes. Our study emphasises the importance of considering stream‐lake connectivity in stream fish assessments, even to shallow seasonally frozen habitats not widely recognised as important. Furthermore, we demonstrate that individuals may use temporary aquatic habitats in complex and changing ways across ontogeny that are not captured by typical classifications of fish movement behaviour.

Arctic lakes located in permafrost regions are susceptible to catastrophic drainage. In this study, we reconstructed historical lake drainage events on the western Arctic Coastal Plain of Alaska between 1955 and 2017 using USGS topographic maps, historical aerial photography (1955), and Landsat Imagery (ca. 1975, ca. 2000, and annually since 2000). We identified 98 lakes larger than 10 ha that partially (>25% of area) or completely drained during the 62‐year period. Decadal‐scale lake drainage rates progressively declined from 2.0 lakes/yr (1955–1975), to 1.6 lakes/yr (1975–2000), and to 1.2 lakes/yr (2000–2017) in the ~30,000‐km²study area. Detailed Landsat trend analysis between 2000 and 2017 identified two years, 2004 and 2006, with a cluster (five or more) of lake drainages probably associated with bank overtopping or headward erosion. To identify future potential lake drainages, we combined the historical lake drainage observations with a geospatial dataset describing lake elevation, hydrologic connectivity, and adjacent lake margin topographic gradients developed with a 5‐m‐resolution digital surface model. We identified ~1900 lakes likely to be prone to drainage in the future. Of the 20 lakes that drained in the most recent study period, 85% were identified in this future lake drainage potential dataset. Our assessment of historical lake drainage magnitude, mechanisms and pathways, and identification of potential future lake drainages provides insights into how arctic lowland landscapes may change and evolve in the coming decades to centuries.