Sniffing the trade-off: Effects of eel odours on nocturnal foraging activity of native and introduced crayfish juveniles

Abstract

Efficient predator avoidance has to be balanced with other fitness-related behaviours such as foraging. Many aquatic animals coexisting with predators can recognise them through chemical cues and respond adaptively. Invasive or introduced species may lack this ability which may result in competitive disadvantage in the presence of predation risk. We investigated behavioural responses of predator-naïve juveniles of two co-occurring crayfish species to chemical cues of European eel (Anguilla anguilla). The native noble crayfish (Astacus astacus) has a long coevolutionary history with eel in Finland and the introduced signal crayfish (Pacifastacus leniusculus) a short one. We found that in the presence of odours from food deprived eels, noble crayfish increased shelter use and reduced nocturnal foraging activity. In contrast, signal crayfish reduced shelter use and increased their foraging activity when exposed to eel odours. These results indicate that signal crayfish would face a stronger risk of predation in waters with eel but the risk is reduced by their overall higher tendency to stay in shelter at night.

Keywords:

• Crayfish
• eel
• Astacus
• Pacifastacus
• Anguilla
• antipredator behaviour
• chemical cues
• risk assessment

Acknowledgements

We thank the Lammi Biological Station and its personnel, especially Ilpo Hakala and Jussi Vilén, for various help and Riitta Savolainen for information on the background of the signal crayfish. Evo Game and Fisheries Research is acknowledged for the eels and crayfish and smooth co-operation. Members of the Crayfish Team gave great support.