Friday 3 January 2014

Terrestrial hunting in European Catfish.

Catfish (Siluriformes) are a large, diverse group of freshwater and shallow marine Fish, found on every continent except Antarctica. They are primarily benthic detrivores, but show a very wide rage of trophic adaptations. They show the widest range of sizes of any group of Boney Fishes, with the smallest species reaching sexual maturity before they grow to 1 cm in length and the largest growing to several meters in length. The European Catfish (or Wels Catfish, Silurus glanis) is the world’s third largest freshwater Fish, and the largest freshwater Fish in Europe reaching up to 4 m long.The Fish is native to Europe east of the Rhine, but has been introduced to a number of waterways in western Europe and further afield, where it appears to be thriving.

In a paper published in the journal PLoS One on 5 December 2012, Julien Cucherousset of the Laboratoire Évolution & DiversitéBiologique at the Université Paul Sabatier and  Stéphanie Boulêtreau, FrédéricAzémar, Arthur Compin, Mathieu Guillaume and Frédéric Santoul of the Laboratoired’Ecologie Fonctionnelle et Environnement, describe a novel hunting method used by European Catfish on the River Tarn in southwestern France.

Large Catfish were observed to deliberately beach themselves on a gravel island beneath a bridge in the city of Albi, in order to catch Feral Pigeons (Columbia livia). A number of Catfish ranging from 90-150 cm in length were observed to engage in this behaviour between June and October 2011. Fifty four separate attacks were observed, with a 28% success rate (i.e the Pigeons were returned to the river and swallowed). The attacks usually lasted less than a second, and always less than four, and more than half of the Fish was out of the water in 40% of attacks (only one, unsuccessful, hunt was observed in which the Fish completely left the water). Only moving Birds were targeted, stationary Pigeons were apparently invisible to the Fish, even when standing at the water’s edge. An isotope study of tissue samples collected from Catfish in the River Tarn revealed varying levels of Pigeon in their diets, with many not consuming any.

European catfish displaying beaching behavior to capture land birds. Cucherousset et al. (2012).

This behaviour has not previously been observed in European Catfish, either inside or out of their native range, suggesting that it is a novel innovation used by Fish on the River Tarn. The fact that only some of the Catfish utilize this strategy supports this, and suggests that this is a learned behaviour. Such behaviour has only previously been observed in Dolphins and Killer Whales (indeed Cucherousset et al. compare the Catfish observed in this study to freshwater Killer Whales), where similar behaviour, along with other hunting or gathering techniques found only in some groups of the animals and apparently learned from one another, are considered to be cultural.

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