Spawning interactions between sympatric brown and brook trout may contribute to species replacement

The behavior of sexually active brook trout Salvelinus fontinalis and brown trout Salmo trutta was observed on spawning redds in a small Minnesota stream to characterize the nature and frequency of interactions between the two species. Twelve redds were continuously monitored for 24 h with underwater video cameras; a total of 270 h of videotape was analyzed. Fifteen spawning events were observed, four of which involved individuals of different species. Male brown trout and brook trout attended females of both species. Female reproductive behavior was similar whether attended by conspecific or heterospecific males. No diel rhythms that would temporally isolate species during spawning were evident. Our results suggest that brook trout and brown trout spawning behaviors do not contribute to reproductive isolation of the two species and that disruptive interactions between them may be common. These interspecific sexual interactions may play a role in species replacement.