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‘‘The giants’ feast’’: predation of the large introduced European catfish on spawning migrating allis shads Ste´phanie Bouleˆtreau . Thomas Fauvel . Marion Laventure . Re´mi Delacour . William Bouyssonnie´ . Fre´de´ric Aze´mar . Fre´de´ric Santoul

Received: 29 July 2020 / Accepted: 3 November 2020 Ó Springer Nature B.V. 2020

Abstract European catfish Silurus glanis is a large non-native opportunistic predator able to develop hunting strategy in response to newly available prey where it has been introduced. Migrating spawning anadromous prey such as allis shad Alosa alosa could represent this available and energy-rich food resource. Here, we report an impressive catfish hunting behavior on shad spawning act in one of the main spawning grounds in Europe (Garonne River, Southwest France). Shad spawning act consists of at least one male and one female swimming side by side, trashing the water surface with their tail which, therefore, produces a splashing noise audible from the river bank. The catfish hunting behavior on shad spawning

Handling Editor: Te´lesphore Sime-Ngando.

Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10452-020-09811-8) contains supplementary material, which is available to authorized users. S. Bouleˆtreau  F. Aze´mar  F. Santoul (&) Laboratoire Ecologie Fonctionnelle et Environnement, Universite´ de Toulouse, CNRS, Toulouse, France e-mail: [email protected] T. Fauvel IMA, 1 rue de Donzac, 64101 Bayonne, France M. Laventure  R. Delacour  W. Bouyssonnie´ MIGADO, 18 Ter rue de la Garonne, 47520 Le Passage, France

act was studied, at night, during spring months, using both auditory and video survey. Simultaneously, catfish individuals were fishing to analyze their stomach content. Catfish disturbed 12% of the 1024 nocturnal spawning acts we heard, and this proportion increased to 37% among the 129 spawning acts when estimated with low-light camera recording. Stomach content analyses on 251 large catfish individuals (body length [ 128 cm) caught in the same river stretch revealed shad represented 88.5% of identified prey items in catfish diet. This work demonstrates that European catfish predation must be considered as a significant factor of mortality of allis shad. In a context of the extension of the European catfish range area in western and southern European freshwaters, this new trophic impact, with other ones previously described for salmon or lamprey, has to be considered in European conservation plans of anadromous species. Keywords Anadromous fish  Diet  Endangered species  Large non-native apex predator  Mating

Introduction Migratory animals in search of food, new habitats or mates, concentrate in time and space, strongly exposing them to predators. The well-known annual migration of wildebeest (Connochaetes taurinus) through

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Aquat Ecol

the Serengeti triggers high densities of adult crocodiles (Crocodylus niloticus) when crossing the Mara River (Subalusky et al. 20