Depth-specific benthic specialization of Arctic char in an oligotrophic subarctic lake

Abstract

Fishes consume prey from across both benthic and pelagic habitats, thereby stabilizing the food webs of freshwater lakes. How fish exploit vertical and horizontal heterogeneity within the benthic environment, however, remains unclear. We characterized spatial variation in the C and N stable isotopes of a dominant benthic grazer (snails) along a water depth gradient in an oligotrophic, western Alaska lake to assess the effects of water depth on isotope characteristics in the benthic food web. Importantly, carbon stable isotopes in snails become substantially more depleted in 13 C with increasing water depth. We compared this distribution of snail isotope values to those found in Arctic char (Salvelinus alpinus) diets to estimate the vertical location of char foraging on benthic resources. We found that Arctic char tended to prey on snails at greater than 10 m depth; however, individual fish specialized at a narrower range of water depths spanning from 5 to > 20 m. We used an isotope mixing model to assess the validity of using only shallow-water benthic invertebrates to represent all benthic resources in food web reconstructions and found that mixing models that only used shallow benthic prey underestimated the importance of benthic resources by about 50%. These results can help refine our understanding of how benthic prey contribute to the stability of aquatic food webs and highlight the need to account for spatial variation in the isotope composition of benthic resources in models of lake food webs.

A systematic review of the trophic ecology of eight ecologically and culturally important fish species in the North American Arctic

“…Smaller individuals feed more on invertebrates, such as chironomids and other aquatic and emergent insects (Online Resource 1, Table 2). Resident Arctic Char in southwest Alaska are more frequently piscivorous, perhaps due to a greater diversity of forage fishes being present in these lower-latitude systems (Woods et al 2013;Fournier and Schindler 2021). Feeding on salmon eggs and juveniles by Arctic Char occasionally occurs in these areas but to a lesser extent than do Dolly Varden, which may feed extensively on salmon eggs and juveniles found in the streams of this region.…”

“…Feeding on salmon eggs and juveniles by Arctic Char occasionally occurs in these areas but to a lesser extent than do Dolly Varden, which may feed extensively on salmon eggs and juveniles found in the streams of this region. Arctic Char tend to occupy lakes and are therefore restricted to preying on Sockeye Salmon (Oncorhynchus nerka) populations which have runs connected to such lakes (Morton 1982;Stewart et al 2009;Dennert et al 2016;Fournier and Schindler 2021). Arctic Char in this region have also been recorded to consume small mammals such as shrews (Woods et al 2013).…”

The Importance of Habitat and Lake Morphometry for the Summer Diet Choice of Landlocked Arctic Char in Two West Greenland Lakes

“…Arctic char (Salvelinus alpinus) is the most widespread freshwater fish in Greenland [9] and is a valued species both commercially and culturally [10]. Furthermore, Arctic char play a fundamental role in the trophic coupling between the pelagic and benthic pathways in such lakes [7,11,12]. Char populations vary substantially in both their morphology and ecology, depending on the environment [13,14].…”

“…Char populations vary substantially in both their morphology and ecology, depending on the environment [13,14]. Several previous studies have examined the dietary niche of char, but have mainly focused on the role of char morphs/ecotypes [11,[14][15][16][17][18] or on the diet of char compared to other fish species [19][20][21].…”