From autochthonous to allochthonous resources: seasonal shifts in food use by stream‐dwellingYOYArctic charrSalvelinus alpinusthrough the ice‐free season

Abstract

Substantial seasonal changes in resource use associated with enhanced water-column use were revealed in stream-living YOY Arctic charr Salvelinus alpinus during the ice-free season. In July, YOY individuals showed a diet dominated by aquatic invertebrates (mainly Chironomidae larvae), but despite the small size of the fish, the abundance of terrestrial insects in their diet increased markedly from July to September (from 1·9 to 62·8%). Similarly, the frequency of surface drifting foragers, i.e. individuals feeding on allochthonous resources, increased from July to September (from 20·6 to 80%); allochthonous resources thus constituting an important energy subsidy for YOY S. alpinus during the late sub-Arctic summer.

Food resource partitioning between stream-dwelling Arctic charr Salvelinus alpinus (L.), Atlantic salmon Salmo salar L. and alpine bullhead Cottus poecilopus Heckel, 1836: an example of water column segregation

“…A previous study has pointed out that surface feeding appears to be rare (\10%) for YOY Arctic charr (Tunney & Steingrímsson, 2012). However, our findings prove that the contribution of surface prey to the diet of Arctic charr may be high (also see Sánchez-Hernández et al, 2016), especially during August and September when some individuals fed almost exclusively on this resource (C70%). In fact, Arctic charr also showed a high capacity to forage on surface-drifting organisms relative to the other two studied species.…”

“…The present study exemplifies how the differences in the use of surface prey (terrestrial prey and emerged aquatic insects) among sympatric species can constitute an important adaptive feature to reduce interspecific competition in riverine fish communities during the summer. Thus, our findings suggest that Studies describing the trophic ecology of Arctic charr in running waters are scarce (but see Moore & Moore, 1974;Stenzel, 1987;Sinnatamby et al, 2012;Sánchez-Hernández et al, 2016). Moore & Moore (1974) observed that small Arctic charr (\100 mm) fed mostly on Chironomidae larvae.…”

“…The diet of stream-dwelling species usually changes seasonally (e.g. Elliott, 1967;Kelly-Quinn & Bracken, 1990;Hubert et al, 1993;Sánchez-Hernández et al, 2016), and our study shows that Arctic charr undergo distinct seasonal shifts in feeding. Diptera was especially important in May and July, Trichoptera in August and Ellipses represent the inertia of each group (here species).…”

“…Young-of-the-year (YOY) Arctic charr have been shown mainly to forage near midwater, but occasionally also utilizing surface and benthic prey (Tunney & Steingrímsson, 2012). However, strong seasonal changes in resource use of YOY Arctic charr, especially in the use of surface prey, have also been documented (Sánchez-Hernández et al, 2016). Based on similar findings from other closely related fish species (see Johnson & Johnson, 1982;Nakano et al, 1999;Mookerji et al, 2004), it is very likely that Arctic charr adopt different foraging modes (benthic or drift) depending upon the available prey to overcome competition with co-occurring species.…”

“…Johnson & McKenna, 2015), whereas few studies have included a seasonal approach (but see e.g. Dineen et al, 2007;Gabler & Amundsen, 2010;Sánchez-Hernández et al, 2016). Noteworthy, it should be kept in mind that seasonal studies may be highly beneficial as ecological processes such as food resource partitioning usually have a marked seasonality.…”