Seasonal Habitat Use of Brook Trout and Juvenile Atlantic Salmon in a Tributary of Lake Ontario

Weak levels of acidification (pH < 6.6) inhibit the ability of fishes to assess predation risk via interference with damage-released chemical alarm cues. While survival benefits associated with behavioural responses to alarm cues have been demonstrated under laboratory conditions, it remains largely unknown whether fishes under natural conditions experience similar benefits. Using hatchery-reared juvenile Atlantic salmon (Salmo salar) as a model organism, we conducted a tethering experiment in reaches of neutral (pH ≥ 6.6) and acidic (pH < 6.6) salmon nursery streams, plus one additional stream that varied between pH classes. Despite exposure to fewer predatory fish species, similar availability of physical refugia, and similar threat from terrestrial predators, tethered fish in acidic streams were significantly more likely to be predated over the course of a trial than their counterparts in neutral streams. These results suggest that (i) in the absence of compensatory mechanisms, juvenile Atlantic salmon under acidic conditions may experience greater rates of predation as a result of impaired chemosensory risk assessment, and (ii) brook trout (Salvelinus fontinalis) appear to play the greatest role in limiting the survival of young-of-the-year (0+) salmon.

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Density-dependent habitat selection by juvenile Atlantic salmon (Salmo salar) in experimental riverine habitats

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f99-074 ◽

1999 ◽

Vol 56 (7) ◽

pp. 1298-1306 ◽

Cited By ~ 25

Author(s):

Tammo P Bult ◽

Stephen C Riley ◽

Richard L Haedrich ◽

R John Gibson ◽

Jan Heggenes

Keyword(s):

Habitat Selection ◽

Population Density ◽

Atlantic Salmon ◽

Habitat Use ◽

Salmo Salar ◽

Implicit Assumption ◽

Experimental Conditions ◽

Density Dependent ◽

Atlantic Salmon Salmo Salar ◽

Juvenile Atlantic Salmon

We investigated habitat use of Atlantic salmon (Salmo salar) parr in experimental riverine enclosures made up of pool, riffle, and run habitats over a range of densities (0.1-1.25 fish·m-2) to test the implicit assumption in habitat modelling that habitat selection does not change with population density. Results indicated that habitat use changed with population density, with relatively more parr in pools and fewer in runs at higher population densities. Temperature influenced parr distribution, with relatively more parr in runs and fewer in riffles and pools at higher temperatures. Parr distribution was primarily affected by hydromorphological differences among pool, riffle, and run habitats. Effects of population density and temperature on use of pool, riffle, and run habitats were often as large as effects of hydromorphological differences among pool, riffle, and run habitats on fish distributions over the range of temperatures and densities observed. Results varied considerably, despite controlled experimental conditions. We concluded that habitat selection by juvenile Atlantic salmon parr may be density dependent and potentially quite variable.

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