Anti-predator behaviour of juvenile Atlantic cod: the role of wild experience and effect of multiple predators

Whitehead, Megan Angharad (2005) Anti-predator behaviour of juvenile Atlantic cod: the role of wild experience and effect of multiple predators. Masters thesis, Memorial University of Newfoundland.

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Abstract

Community structure is largely influenced by predator-prey interactions; however, the complex nature of anti-predator behaviours, especially when more than one predator is present, remains unclear. The work outlined in this thesis investigated the effect of experience with multiple predators on the anti-predator behaviour of juvenile Atlantic cod (Gadus morhua). Hatchery-reared ("naive") individuals lacking the experience of their wild counterparts may be unable to recognize or evade predators effectively. The anti-predator behaviour of naive juvenile cod and two wild cod species, Atlantic cod and rock cod (Gadus ogac) in the presence of either one or two shorthorn sculpin, was examined. Both wild species demonstrated schooling behaviour in the presence of a predator, and no predation was observed over the course of the trials. However, effective schooling behaviour, as determined by relative mortality, was not observed with the naive Atlantic cod as predation was observed in 50% of the trials. -- The effect of multiple predators on schooling behaviour and mortality was also investigated in naive juvenile Atlantic cod exposed to both adult cod and sculpin in a substitutive design. Non-additive effects on the relative mortality of juvenile Atlantic cod under multiple predator threat were observed, while the effects on schooling behaviour were less clear. This study was the first to investigate multiple predator effects in Atlantic cod, and one of the first marine studies in the multiple predator effects literature. The results demonstrate the plasticity of prey responses and the importance of experience in the development of efficient anti-predator behaviours.

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