Sensory complementation and antipredator behavioural compensation in acid-impacted juvenile Atlantic salmon
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Prey incorporate multiple forms of publicly available information on predation risk into threat-sensitive antipredator behaviours. Changes in information availability have previously been demonstrated to elicit transient alterations in behavioural patterns, while the effects of long-term deprivation of particular forms of information remain largely unexplored. Damage-released chemical alarm cues from the epidermis of fishes are rendered non-functional under weakly acidic conditions (pH < 6.6), depriving fish of an important source of information on predation risk in acidified waterbodies. We addressed the effects of long-term deprivation on the antipredator responses to different combinations of chemical and visual threat cues via in situ observations of wild, free-swimming 0+ Atlantic salmon (Salmo salar) fry in four neutral and four weakly acidic nursery streams. In addition, a cross-population transplant experiment and natural interannual variation in acidity enabled the examination of provenance and environment as causes of the observed differences in response. Fish living under weakly acidic conditions demonstrate significantly greater or hypersensitive antipredator responses to visual cues compared to fish under neutral conditions. Under neutral conditions, fish demonstrate complementary (additive or synergistic) effects of paired visual and chemical cues consistent with threat-sensitive responses. Cross-population transplants and interannual comparisons of responses strongly support the conclusion that differences in antipredator responses between neutral and weakly acidic streams result from the loss of chemical information on predation risk, as opposed to population-derived differences in behaviours.
KeywordsPredator–prey interactions Threat-sensitivity Public information Damage-released chemical cues Risk assessment
The authors thank R. Cunjak (University of New Brunswick) and M. Hambrook (Miramichi Salmon Association) for logistic and technical support. C.D. Jackson, K. Paquin, M. Romano, T.I. Laakkonen, P.H. Malka, M. Tresidder, J. Dumont, A. Schaffer, A. Fraser, L.J. Mancini, J. Beam and D. Thibodeau provided assistance in the field. This work was supported by grants from le Fonds québécois de la récherche sur la nature et les technologies (FQRNT) to C.K. Elvidge and the Natural Sciences and Engineering Research Council of Canada (NSERC) and Concordia University to G.E. Brown. All work was conducted with the approval of Fisheries & Oceans Canada (scientific licence # SG-NBT-09-050) and in accordance with Concordia University Animal Research Ethics protocol AREC-2008-BROW. This manuscript is contribution no. 122 to the Catamaran Brook Habitat Research Project.
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