Prey Selection of Subyearling Atlantic Salmon and Rainbow Trout Coexisting in a Natural Stream

Abstract

Atlantic salmon (Salmo salar) and rainbow trout (OncovCiynchus mykiss) are similar ecologically but share no coevolutionary histoly favoring the evolution of niche-partitioning mechanisms. Therefore, interspecifi c competition may occur as each species becomes naturalized throughout the other's native range. As a first step towards investigating competitive interactions, we tested hypotheses regarding prey selection in allopatric and sympatric populations of Atlantic salmon and rainbow trout in a natural stream. Diet samples from 184 fish and contemporary drift samples were collected during a 24-hour period in mid-summer. Diet overlap was low between salmon and trout in allopatry, but high in sympatry. Salmon consumed more prey and a greater proportion of baetid mayflies than did trout, which fed more frequently on chironomid larvae and aerial-terrestrial invertebrates. Both species consumed larger prey when allopatric than when sympatric. Salinon in allopatry fed as generalists and trout in allopatry fed as specialists, but diets converged when in syinpatry. Feeding habits of both salmonines seemed to be affected by the other's presence, although more notably for trout. Results were more consistent with predictions based on optimal foraging theory than on niche-partitioning theory.

Prey trait analysis shows differences in summer feeding habitat use between wild YOY Atlantic salmon and brown trout

“…On the other hand, Pedley and Jones (1978) stated that interspecific competition between S. salar and S. trutta was only significant during the summer months when food was abundant. Our results, using the Schoener's index, suggest a remarkable similarity in prey utilization patterns between species as previously stated by other researchers (Gibson & Cunjak 1986;Coghlan et al 2007). However, the high overlap values found in the present study might not indicate competition, for two reasons.…”

“…Several authors have found that diet overlap is high between Atlantic salmon and other salmonids species in sympatry (Gibson & Cunjak 1986;Coghlan et al 2007). In a previous study in Spain, Suárez et al (1988) found significant interspecific differences in the diet between S. salar and S. trutta in May and November, although they did not find differences in April and July.…”

Feeding habits of the alien brook trout Salvelinus fontinalis and the native brown trout Salmo trutta in Czech mountain streams

“…for interspecific competition (Coghlan et al, 2007). Our results show that in the season with a high feeding intensity (reflected in high stomach fullness), there was a lower dietary overlap in comparison with the periods when feeding intensity declined.…”

“…Diets containing more terrestrial invertebrates in one of the two coexisting species have been reported by several studies on related species of salmonids (Coghlan et al, 2007;McHugh et al, 2008;Wilson et al, 2014). Such shifts may be caused by differences in prey utilization, as well as by changes in habitat use when the dominant species outcompetes subordinates from favourable feeding positions (Blanchet et al, 2007).…”

“…McHugh et al (2008) reported percent diet overlaps between brown and cutthroat trout of 87.5% and 89.5%, which are higher values in comparison to those found in our study, where the diet overlap attained a maximum of 81.5%. Low diet overlap between Atlantic salmon and rainbow trout in allopatry, but high in sympatry were found by Coghlan et al (2007).…”