A specialised cannibalistic Arctic charr morph in the piscivore guild of a subarctic lake
Arctic charr (Salvelinus alpinus) is generally considered an inferior piscivore compared to brown trout (Salmo trutta). However, we demonstrate that a recently described profundal spawning piscivore PP-morph of Arctic charr in a subarctic lake has evolved typical piscivore traits (i.e. large jaws, robust skulls), similar to the co-occurring brown trout but different from the sympatric littoral spawning omnivore LO-morph of Arctic charr. A few large-sized LO-morph, most large-sized PP-morph and trout constitute the piscivore guild, but they differed in prey fish selection. Of the fish-eating deep-water PP-morph, 52% had consumed charr, with a peak during the polar night period (68–80% in November–January). In contrast, the LO-morph and trout were mainly (~90%) inter-specific piscivores eating stickleback. Consequently, the PP-morph was the main charr predator and started to feed on fish at a smaller size and took larger prey relative to their body length than the trout. Stable isotope (δ13C, δ15N) ratios reflect the dietary specialisations in the upper-water (LO-morph, trout) and the deep-water (PP-morph) environments, besides the piscivorous behaviour of the PP-morph and trout. The existence of a shallow-water piscivore (trout) may explain the origin of this PP-morph, taking benefit of underutilised resources of small-sized Arctic charr in the deep-water habitat.
KeywordsProfundal Tri-morphism Salvelinus alpinus Brown trout Salmo trutta Prey fish
We acknowledge the fieldwork assistance from our Department Engineers: Cesilie Bye, Laina Dalsbø and Karin S. Johannessen, and former Master-students: Kristin Johansen, Sigrid Skoglund, Aslak Smalås and John F. Strøm. Marianne Simonsen has placed landmarks on the photographs for the analyses of the morphological traits. Sigrid Skoglund made the drawing of the head of Arctic charr. We also thank the Guest Editor and the Assistant Editor for their support, and R.N. Sinnatamby and one anonymous referee for very constructive and helpful reviews.
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