Seasonal and ontogenetic variations in resource use by two sympatric Arctic charr morphs

Abstract

The study compares the resource utilization of two sympatric Arctic charr morphs over an annual period in a subarctic lake. The two morphs are reproductively isolated in time and place of spawning, and are referred to as the littoral and profundal morphs (L-morph and P-morph) according to their spawning habitats. Fish were sampled monthly (icefree season) or bimonthly (winter) using gillnets in the main lake habitats. The spatial range of the P-morph was restricted to the profundal zone throughout the whole annual period. The L-morph in contrast utilized all main habitats, exhibiting distinct seasonal and ontogenetic variations in habitat distribution. In the spring, the whole L-morph population was located along the bottom profile of the lake, in profundal and littoral habitats. During summer and autumn, habitat segregation occurred between different life-stages, juveniles mainly utilizing the profundal, pre-adults the pelagic and adult fishes the littoral zone. During winter the whole population was assembled in the littoral habitat. The L-morph also had large seasonal and ontogenetic variations in their feeding ecology, with littoral zoobenthos, zooplankton and surface insects being important prey. The P-morph had a narrower diet niche mainly consisting of chironomid larvae and other profundal zoobenthos. Hence, the two Arctic charr morphs exhibited a consistent resource differentiation during all annual seasons and throughout their life cycles, except for a dietary overlap between P-morph and juvenile L-morph charr in the profundal during summer. The findings are discussed in relation to resource polymorphism and incipient speciation.

Winter ecology of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in a subarctic lake, Norway

“…This may be related to the observation that small charr are likely to starve to death during winter if they are unable to feed , and the availability of food resources is therefore a critical factor for their survival during this period. Zooplankton, which is an important food resource for juvenile charr during the ice-free period (Klemetsen et al 1992(Klemetsen et al , 2003aAmundsen et al 2008), is generally low in abundance during winter.…”

“…Arctic charr is known as a species that is more adopted to coldwater than brown trout (Klemetsen et al 2003a) and able to feed during wintertime (e.g., Parker and Johnson 1991;Hammar 1998;Klemetsen et al 2003b;Svenning et al 2007;Amundsen et al 2008). The feeding of brown trout in winter is more surprising as the brown trout is known as a typical visual predator requiring good light conditions for efficient feeding (Langeland et al 1991;Mazur and Beauchamp 2003).…”

“…The study lake harbours two different morphs of Arctic charr, one littoral spawning morph (L-morph) and one profundal spawning, dwarf-like morph (P-morph) that differ distinctly in their ecology, morphology and genetics (Klemetsen et al 1997(Klemetsen et al , 2002Westgaard et al 2004;Knudsen et al 2006Knudsen et al , 2007Amundsen et al 2008). The L-morph charr resemble the Arctic charr populations found in other lakes in the region (Klemetsen et al 1997;Knudsen et al 2006), whereas the dwarfed P-morph charr appear to be confined to a rare and untypical ecological niche for the species, residing their whole life in the profundal zone and feeding on typical profundal prey from the soft-bottom sediments (Klemetsen et al 1997(Klemetsen et al , 2002(Klemetsen et al , 2003aKnudsen et al 2006;Amundsen et al 2008). The P-morph charr have therefore not been included in our interspecific comparison of Arctic charr and brown trout.…”

Morphological, ecological and behavioural differentiation of sympatric profundal and pelagic Arctic charr (Salvelinus alpinus) in Loch Dughaill Scotland

“…This is particularly true for fishes in postglacial lakes (Taylor & McPhail, 1999;Jonsson & Jonsson, 2001;Østbye et al, 2006) and results in alternative phenotypes living in sympatry within a single lake . This is seen in Arctic charr, Salvelinus alpinus (Linnaeus 1758) in which the structuring is based on the adaptation of foraging specialisms to alternative food resources (Malmquist et al, 1992;Adams et al, 1998;Amundsen et al, 2008;Garduño-Paz et al, 2010). Referred to as resource polymorphisms, they are frequently identified by the expression of different morphological phenotypes, foraging ecology and differences in diet (Smith & Skúlason, 1996).…”

“…Loch Tay (Scotland) (Adams et al, 2003;Garduño-Paz et al, 2010). The most commonly reported foraging divergence seen in sympatric populations of Arctic charr is that of a divergence into planktonic and littoral-zoobenthos feeding (Malmquist et al, 1992;Adams et al, 1998Adams et al, , 2003Adams & Huntingford, 2002;Amundsen et al, 2008, Corrigan et al, 2011Garduño-Paz et al, 2012).…”