New research shows that salmon can identify and avoid otters that have been eating other salmon.
Researchers at the University of Swansea tested salmon behaviour in relation to the predators' scent using diluted faeces. The fish were placed in a specially constructed 'Y' shaped tank where the predatory pong could be released into one arm while the other was either left clear, or scented with the faeces of an otter than had not eaten salmon.
The avoidance behaviour of the fish was monitored and it was shown that the fish stayed clear of the salmon eater's smell 85% of the time choosing the clear arm instead, but were not scared off by the salmon-friendly otters' aroma showing that the otters' diet is the key factor.
Frightened fish also displayed behaviours such as increased breathing rates and 'freezing' motionless at the tank's bottom in the presence of the salmon-loving otters smell; both behaviours associated with stress and predator avoidance.
Interestingly even young fish which had never encountered the predator before displayed the same behaviour, suggesting the ability is hardwired in the species rather than learned through experience.
This newly discovered sensory ability gives the fish a 'heads-up' of any potential predators in the area before they see them and allows them to better balance vital activities such as feeding against the risk of being eaten.
Earlier studies had shown that some fish species can detect the presence of predatory fish in their environment, but this is the first evidence that the mechanisms involved can work with mammalian predators too.
For more information see the paper: Laura Jayne Roberts and Carlos Garcia de Leaniz. Something smells fishy: predator-naive salmon use diet cues, not kairomones, to recognise a sympatric mammalian predator. Animal Behaviour, 2011, doi: 10.1016/j.anbehav.2011.06.019
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