Dynamics of residency for brook charr (Salvelinus fontinalis) in Lake Superior tributaries
I investigated stream residency for brook charr ('Salvelinus fontinalis ') inhabiting six Lake Superior tributaries. Emerging evidence suggests Lake Superior brook charr exhibit partial migration, with a small type of brook charr that purportedly remains in its natal stream habitat for its lifetime and a large type residing in the lake that purportedly migrates from the stream to the lake as a juvenile and returns to the stream to spawn. The hypothesis that small stream fish remain resident has never been tested critically. Electro-fishing surveys, passive integrated transponder tags, and stable isotopes were used to test whether the movement and habitat use of 320 brook chary captured and tagged in streams was most consistent with six alternative hypotheses: stream residency, emigration from the stream to lake, movement to adjacent streams, diel migration, crepuscular migration, or haphazard habitat switching. 90% of tagged brook charr were consistent with the stream residency, 2% were consistent with emigration from a stream, none (0%) were consistent with movement to adjacent stream, and 8% were most consistent with diel migration. My findings support the hypothesis of partial migration and demonstrate how rigorous tests of residency can contribute to research programs delineating the nature of complex migratory systems.