The effect of habitat complexity on Atlantic salmon behaviour

• Main Author: Bilhete, Caroline
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: Atlantic salmon
• Online Access: https://spectrum.library.concordia.ca/id/eprint/979753/; https://spectrum.library.concordia.ca/id/eprint/979753/3/Bilhete_MSc_S2015_.pdf

An increase in habitat complexity is thought to decrease visibility and the territory size of visually-oriented animals. Hence, the addition of physical structure has been viewed as a restoration technique, particularly in streams, to increase the density of target species. However, a decrease in territory size may have a negative effect on the fitness of individual organisms. This project is a first attempt to evaluate the effects of habitat structure on the behaviour and growth rate of wild young-of-the-year (YOY) Atlantic salmon. Fish were exposed to one of two habitat treatments in mesh enclosures in Catamaran Brook, New Brunswick: a fine gravel substrate (low complexity) or a fine gravel substrate with boulders added (high complexity). Wild-caught individuals were tagged, weighed and measured before being stocked at densities of ~ 1m2 for seven day trials. Fish from high complexity environments exhibited a decrease in foraging rate, frequency of aggression, territory size compared to their counterparts from low complexity environments. Specific growth rate, however, did not differ significantly between treatments. While the addition of structure to a habitat may be beneficial at the population level in terms of an increase in population density, our results suggest that individual fish may pay a cost in terms of a decrease in foraging rate and territory size in these environments. Further research is needed to evaluate the costs and benefits of adding structure to improve the habitat quality for stream salmonids.