Selective segregation in intraspecific competition between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Abstract

Interactive segregation has been suggested as the ruling competition mechanism determining niche and niche segregation between juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Results from allopatry-sympatry observations of habitat use in both nature and in experiments were contrary to predictions derived from the interactive segregation hypothesis. Habitat use parameters under natural conditions such as distance to shore for Atlantic salmon parr were nearly identical in allopatric (mean AE SD; 3.2 AE 1.4 m) and sympatric (3.3 AE 1.4 m) situations. Occupied water depths largely reflected available water, but water depths <15 cm were avoided by salmon parr. Under experimental conditions, habitat use of allopatric salmon was density independent and salmon size had only minor effects, with smaller fish being more likely to occur in the shallow. Habitat use of salmon in sympatry with trout did not differ from allopatric salmon habitat use, and only salmon size had minor effects on depth choice -occurrence of trout or fish density had no effect. Allopatric trout was in general more frequent in the shallow habitat than salmon. Habitat use of sympatric trout was affected by the occurrence of salmon and trout size, resulting in a higher use of the shallow habitats for small trout. To conclude, selective segregation has a dominant role in salmon habitat use (not affected by trout occurrence), whereas a mixed situation occurs in trout habitat use with elements of interactive segregation when competing with Atlantic salmon (affected by salmon occurrence).

Mitigation of acidified salmon rivers – effects of liming on young brown troutSalmo trutta

“…Thus, the recovery of S. salar may have influenced the density of sympatric S. trutta negatively. These two species are among the most abundant freshwater fishes in Scandinavian rivers, where they compete for space and food (Kalleberg, ; Stradmeyer et al ., ; Berg et al ., ). Salmo salar and S. trutta are often spatially segregated with juveniles of the former typically occurring further offshore and in deeper habitats than S. trutta , presumably due to strong interference interactions (Heggenes et al ., ).…”

Hydraulic classification of hydropeaking stages in a river reach

“…Likewise, dewatering of shallows is associated with stranding, and hence suffocation, of juveniles (Saltveit, Brabrand, Juárez, Stickler, & Dønnum, 2020; Saltveit, Halleraker, Arnekleiv, & Harby, 2001) as well as entrapment of salmonids (Halleraker et al, 2003). Moreover, in rivers where both Atlantic salmon ( Salmo salar ) and brown trout ( Salmo trutta ) coexist, Atlantic salmon tend to inhabit the deeper areas, displacing the brown trout to the shallows (Berg, Bremset, Puffer, & Hanssen, 2014; Bremset & Berg, 1999; Bremset & Heggenes, 2001). As a result, brown trout are at increased stranding and entrapment risk.…”

Dry season survival of juvenile salmonids in an intermittent coastal stream

“…For example, body size plays a critical role in survival of 69 stream fishes. Territoriality and aggressive behavior are well-documented in many stream fishes 70 (Gerking 1953;Titus 1990;Young 2004), with smaller fish often displaced from optimal habitat 71 by larger conspecifics (Bohlin 1977;Berg et al 2014) or the presence of large piscivores (Power 72 D r a f t 4 In this study, we tracked the fates of imperiled salmonid fishes in an intermittent coastal 80 stream in California across four dry seasons that differed in antecedent precipitation. Our goal 81 was to estimate over-summer survival of juvenile salmonids and explore among-and within-year 82 variation in survival.…”