Fine-scale habitat use and behaviour of Arctic charr (Salvelinus alpinus) morphs in a remote Arctic lake

Abstract

The Arctic charr (Salvelinus alpinus) is the most northerly distributed species of freshwater fish and is biologically and culturally important throughout the Arctic region. Lacustrine populations of high-latitude Arctic charr exhibit considerable phenotypic variability, specifically adapted to occupy multiple niches in order to maximise the limited resources available. The inhospitable environment, in which this species can reside, creates difficulties in studying this species in all seasons, with research under ice severely limited. The objectives of this study were to determine whether phenotypic variation influences the spatial behaviour of Arctic charr and to investigate the year-round strategies of this species.
An autonomous acoustic telemetry positioning system was deployed to record the near complete, 3-dimensional spatial distribution of 28 acoustically tagged Arctic charr, from an Arctic lake, Lake Ellasjøen (surface area; 0.72 km2, max depth; 34 m) on Bear Island (74° N) over a 12 month period (September 2009–2010). Discriminant analysis of meristic data identified sympatric morphotypes within the study sample.
Spatial distribution (lake zone habitat, fish depth and fish distance from lake bed) space use (core and excursive home range area) and activity were compared for two morphs; a robust littoral form and a delicate limnetic form. Each morph exhibited discrete habitat use over almost the entire study period and divergence in space use and activity reflected different behavioural patterns. Both phenotypes exhibited similar behavioural responses to the Arctic annual cycle, with fish less active under ice, however diel patterns of fish activity were observed during polar night, autumn and spring which were absent during the months of polar day (May – July).
These findings likely manifest as a result of resource-driven divergence of morphs in a harsh, Arctic environment. Seasonal behavioural adaptations reveal dynamic responses to the Arctic year, warranting further attention, particularly in light of predicted climate change in this region.