Intra- and inter-specific competition for winter concealment habitat in juvenile salmonids

The availability of streambed refuges has previously been shown to be of critical importance to the survival of overwintering juvenile salmonids. We used semi-natural stream channels to quantify intra- and inter-specific competition for daytime refuges and the willingness of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) to share available shelter. Refuge use was frequently associated with aggressive behaviour when two fish were provided with only one shelter, with intra- and inter-specific competition being similar in intensity. Resident individuals were less likely to leave the refuge than were intruders, and sharing of refuges was uncommon, both when competing for one shelter (experiment I) and when these were provided in excess (experiment II). Fish showed greater preferences for foraging habitat during the night than for the location of daytime shelters and were therefore willing to shift habitats to find adequate shelter. Overall, these results suggest that winter competition for refuges, both within and between species of salmonid, is likely to be intense if refuge availability is limited in the wild.

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Maintenance of asymmetric hybridization between Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) via postzygotic barriers and paternal effects

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f2011-004 ◽

2011 ◽

Vol 68 (4) ◽

pp. 593-602 ◽

Cited By ~ 17

Author(s):

David Álvarez ◽

Eva Garcia-Vazquez

Keyword(s):

Atlantic Salmon ◽

Salmo Salar ◽

Brown Trout ◽

Salmo Trutta ◽

Developmental Rate ◽

Paternal Effects ◽

Atlantic Salmon Salmo Salar ◽

Postzygotic Barriers ◽

Brown Trout Salmo Trutta ◽

In The Wild

At the southern European edge of Atlantic salmon ( Salmo salar ) distribution, all the hybrids found in nature are the product of crosses between female salmon and male brown trout ( Salmo trutta ). By artificially producing reciprocal crosses between salmon and trout, we demonstrate that unidirectional hybridization observed in nature is the result of postzygotic barriers that produce very high mortality rates (95%) in female trout × male salmon hybrids and not the consequence of prezygotic isolation or behavioural differences between the two species. Mortality of female trout × male salmon hybrids mainly occurs during the last phases of development, and a high percentage of these surviving hybrids showed external deformities that could compromise survival in the wild. Another important finding is the existence of paternal factor in embryo development. Using time to midhatch as an indicator of developmental rate, female salmon × male trout hybrids hatched faster than female trout × male salmon hybrids, with both developing at a rate intermediate to the pure crosses. The early emergence of female salmon × male trout hybrids, which have similar survival to pure salmons, could have fitness repercussions, since early emerging fry have a competitive advantage over later emerging fry.

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Spatial and temporal effects of interspecific competition between Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in winter

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f01-061 ◽

2001 ◽

Vol 58 (6) ◽

pp. 1133-1140 ◽

Cited By ~ 32

Author(s):

A J Harwood ◽

N B Metcalfe ◽

J D Armstrong ◽

S W Griffiths

Keyword(s):

Atlantic Salmon ◽

Salmo Salar ◽

Brown Trout ◽

Salmo Trutta ◽

Habitat Preferences ◽

Flowing Water ◽

Stream Channels ◽

Growth And Survival ◽

Atlantic Salmon Salmo Salar ◽

Brown Trout Salmo Trutta

Previous work has shown that juvenile stream-dwelling salmonids become predominantly nocturnal during winter by emerging from daytime refuges to feed, with several species having been shown to prefer slow-flowing water while active at night. We used seminatural stream channels, landscaped to provide a choice of water depths, and hence velocities, to test whether Atlantic salmon, Salmo salar, and brown trout, Salmo trutta, show similar habitat preferences during winter. We also tested whether there was any spatial or temporal displacement of Atlantic salmon when in sympatry with brown trout. Nighttime observations revealed that Atlantic salmon did have a preference for slow-flowing water. However, when in direct competition with trout, salmon either remained predominantly nocturnal but occupied shallower water, or became significantly less nocturnal, spending more time active during the day than when in allopatry. These results, which were especially marked in relatively larger fish, indicate that competition between the two species for food and resources is not restricted to the summer months and may affect both the short- and long-term growth and survival of overwintering wild Atlantic salmon.

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