Brown trout (Salmo trutta L. 1758) and Arctic charr [Salvelinus alpinus (L. 1758)] display different marine behaviour and feeding strategies in sympatry.

Brown trout (Salmo trutta L. 1758) and Arctic charr [Salvelinus alpinus (L. 1758)] tagged with acoustic transmitters migrated from fresh water to the sea mainly in May and June, but with large individual variation in migration timing. For S. trutta, large individuals (42-86 cm total length) migrated earlier in the season than small individuals (18-27 cm). For S. alpinus, no such pattern was found, likely because of the small size range of tagged fish (28-41 cm). S. trutta stayed longer at sea than S. alpinus (average 2 vs. 1 month). Early migrants of S. trutta stayed for a shorter period at sea than late migrants, whereas no such pattern was observed for S. alpinus. Large S. trutta moved quickly away from the river and spent average 3 days to reach a receiver line 20 km from the river mouth, whereas small S. trutta and S. alpinus migrating that far spent 2-3 weeks on the same distance. S. trutta utilized the entire fjord system and had a greater proportion of long-distance migrants (>20 km, 78% and 59% of large and small S. trutta, respectively) than S. alpinus (29%). S. alpinus mostly stayed in the inner fjord areas, and none were recorded in the outermost part of the fjord. The difference in the use of marine areas may be caused by variation in prey choice and spatial distribution of the preferred prey groups. Stable isotope analysis showed that S. trutta had been feeding at a higher trophic level than S. alpinus. S. trutta had mainly fed on marine fish and shrimps, whereas S. alpinus had large proportions of freshwater invertebrates in the diet, suggesting that the estuary with benthos and amphipods drifting from the river was an important feeding habitat for S. alpinus. In conclusion, major differences in habitat use, migration patterns and feeding strategies were found between sympatric anadromous S. trutta and S. alpinus while at sea.

Marine habitat use and feeding ecology of introduced anadromous brown trout at the colonization front of the sub-Antarctic Kerguelen archipelago.

In 1954, brown trout were introduced to the Kerguelen archipelago (49°S, 70°E), a pristine, sub-Antarctic environment previously devoid of native freshwater fishes. Trout began spreading rapidly via coastal waters to colonize adjacent watersheds, however, recent and unexpectedly the spread has slowed. To better understand the ecology of the brown trout here, and why their expansion has slowed, we documented the marine habitat use, foraging ecology, and environmental conditions experienced over one year by 50 acoustically tagged individuals at the colonization front. Trout mainly utilized the marine habitat proximate to their tagging site, ranging no further than 7 km and not entering any uncolonized watersheds. Nutritional indicators showed that trout were in good condition at the time of tagging. Stomach contents and isotope signatures in muscle of additional trout revealed a diet of amphipods (68%), fish (23%), isopods (6%), and zooplankton (6%). The small migration distances observed, presence of suitable habitat, and rich local foraging opportunities suggest that trout can achieve their resource needs close to their home rivers. This may explain why the expansion of brown trout at Kerguelen has slowed.

Genetic versus rearing-environment effects on phenotype: hatchery and natural rearing effects on hatchery- and wild-born coho salmon.

With the current trends in climate and fisheries, well-designed mitigative strategies for conserving fish stocks may become increasingly necessary. The poor post-release survival of hatchery-reared Pacific salmon indicates that salmon enhancement programs require assessment. The objective of this study was to determine the relative roles that genotype and rearing environment play in the phenotypic expression of young salmon, including their survival, growth, physiology, swimming endurance, predator avoidance and migratory behaviour. Wild- and hatchery-born coho salmon adults (Oncorhynchus kisutch) returning to the Chehalis River in British Columbia, Canada, were crossed to create pure hatchery, pure wild, and hybrid offspring. A proportion of the progeny from each cross was reared in a traditional hatchery environment, whereas the remaining fry were reared naturally in a contained side channel. The resulting phenotypic differences between replicates, between rearing environments, and between cross types were compared. While there were few phenotypic differences noted between genetic groups reared in the same habitat, rearing environment played a significant role in smolt size, survival, swimming endurance, predator avoidance and migratory behaviour. The lack of any observed genetic differences between wild- and hatchery-born salmon may be due to the long-term mixing of these genotypes from hatchery introgression into wild populations, or conversely, due to strong selection in nature--capable of maintaining highly fit genotypes whether or not fish have experienced part of their life history under cultured conditions.