Wels Catfish
(Silurus glanis)
is an introduced species, found in many areas of Europe including southwestern
France, Italy and Spain. It is the largest freshwater fish in Europe, and the
third largest fish in the world (Copp et al. 2009). Preying usually on small
crustaceans, other fish, the occasional human remains and even cannibalism, the
opportunistic catfish have found a new and more unusual idea of a meal: pigeons.
The catfish
have evolved to hunt in low visibility waters, which has significantly reduced
the size of their eyes and their eyesight capabilities. Instead, they have
taste organs on their barbels, lips, fins and skin of their head and body. In
addition to this, their barbels have an electroreceptive system to pick up
movement in the water, and highly sensitive hearing, which is specialized for
the water. Their hearing organ is attached to their swim bladder, which
amplifies any sounds in the water (Copp et al. 2009).
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| Image: Brian Coad - www.briancoad.com |
In
an area of the Tarn River, a study was conducted on the behavior and hunting of
Wels Catfish. This particular area is protected, and angling is prohibited. A
gravel island was observed, a popular place where pigeons land to clean
themselves and drink from the river. The catfish were observed waiting by the edge
of the water, supposedly attracted by the sound of movement in the water
produced by the birds.
Similar to marine mammals such as dolphins and killer
whales, the catfish were seen beaching themselves and successfully capturing
pigeons from the waters edge.
This is considered highly unusual, even for an
opportunistic animal such as the catfish. The strategy involves the hunting of
prey that is outside the predator’s ecosystem boundaries (Cucherousset
et. al, 2012).
This risky behavior may be associated with a lack of prey abundance, as
a study conducted in 2005 found that prey abundance is influenced by water
temperature. Stomach contents of Wels Catfish were analyzed, and it was found
that areas with higher water temperatures had catfish with fuller stomachs
(Wysujack & Mehner, 2005). This may suggest a more desperate hunting tactic
in areas with less prey availability, or simply the surprising ability of the
catfish to adapt to its new surroundings and a wider range of prey.
See the video below, thanks to Animal Wire!
References
Copp, G. H., Robert Britton, J., Cucherousset, J., García-Berthou, E.,
Kirk, R., Peeler, E. and Stakėnas, S. (2009), Voracious invader or benign
feline? A review of the environmental biology of European catfish Silurus
glanis in its native and introduced ranges. Fish and Fisheries,
10: 252–282. doi: 10.1111/j.1467-2979.2008.00321.x
Julien Cucherousset, Stéphanie Boulêtreau, Frédéric Azémar, Arthur
Compin, Mathieu Guillaume, Frédéric Santoul (2012)
“Freshwater Killer Whales”: Beaching Behavior of an Alien Fish to Hunt Land
Birds. PLoS ONE 7(12): e50840. doi:10.1371/journal.pone.0050840
Wysujack, K., Mehner, T. (2005) Can feeding of European
catfish prevent cyprinids from reaching a size refuge? Ecology of Freshwater
Fish. 14; 87 - 95
Yet another very cool and very odd hunting strategy! Where does this fish originate from? Have there been examples of novel hunting strategies evolving in original populations? I was also wondering if there has been a corresponding shift in vigilance or anti-predator behaviour in the pigeons in this region? Very interesting.
ReplyDeleteHi Tasmin!
DeleteWels catfish is native to areas of central, eastern and southern Europe, but they have been introduced to wider areas like Greece, the UK and even Kazhakstan. This paper seemed to say that the behaviour was specific to this population, who used a particular gravel island that was popular to pigeons. No word on the pigeons reaction though, but I wouldn't be surprised if they stopped going to that part of the river soon..