Habitat segregation by sympatric juvenile Arctic charr and brown trout in shallow lake areas: a consequence of interspecifc diferences in predator avoidance?

In sympatry, juvenile brown trout (Salmo trutta) usually occupy the shallow and most productive areas (littoral zone) of lakes, while juveniles of Arctic charr (Salvelinus alpinus) are found in deeper, less productive parts. In contrast, when Arctic charr juveniles occur in allopatry, they often occupy shallow littoral areas as well. Habitat segregation has traditionally been interpreted as a trade-of between predation risk and energy gain, while the segregation of these two species has been explained by brown trout being more aggressive and competitively superior to Arctic charr. We hypothesize, however, that the marked habitat segregation between the two species may also be due to diferences in predator avoidance. Accordingly, we conducted several laboratory tests, using Arctic charr and brown trout as potential predators. Live fsh of the same species were ofered as prey, either as small charr only, small trout only, or both small charr and small trout together. Artifcial shelters were then introduced to examine the avoidance ability of prey fsh against predatory fsh. Our results showed that under these circumstances, access to shelters strongly decreased mortality in juvenile brown trout, but had no efect on juvenile Arctic charr mortality. Thus, the habitat segregation shown by sympatric juvenile Arctic charr and brown trout in lakes may be a consequence of interspecifc diferences in predator avoidance. Juvenile salmonids · Habitat use · Competition · Shelter · Predator avoidance