Diet segregation between introduced bullhead (Cottus gobio L.) and Atlantic salmon parr (Salmo salar L.) in a sub-Arctic river

Abstract

The diets of accidentally introduced bullhead and native salmon parr were studied in River Utsjoki, a tributary to the watercourse River Tana, one of the most important river habitats in Europe for the declining Atlantic salmon. Food resource partitioning was studied in sympatry during the summer and autumn seasons and compared with allopatric situations. We found a consistent segregation in food niche between the two species. Both salmon parr and bullhead predominantly utilised the benthic feeding habitat, but the bullhead mostly ate interstitial prey whereas salmon parr mainly consumed prey associated with the substrate surface. Furthermore, the salmon parr fed more on drift than the obligate benthivore bullhead. This study documents a selective segregation in food niche between a benthic and a drift-feeding fish in running water. At present there is little evidence of competition between the species, but potential competition for food is discussed.