“The giants’ feast”: predation of the large introduced European catfish on spawning migrating allis shads Stéphanie Boulêtreau, Thomas Fauvel, Marion Laventure, Rémi Delacour, William Bouyssonnié, Frédéric Azémar & Frédéric Santoul Aquatic Ecology A Multidisciplinary Journal Relating to Processes and Structures at Different Organizational Levels ISSN 1386-2588 Aquat Ecol DOI 10.1007/s10452-020-09811-8 1 23 Your article is protected by copyright and all rights are held exclusively by Springer Nature B.V.. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Aquat Ecol https://doi.org/10.1007/s10452-020-09811-8 (0123456789().,-volV)( 0123456789().,-volV) ‘‘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 act was studied, at night, during spring months, using non-native opportunistic predator able to develop both auditory and video survey. Simultaneously, hunting strategy in response to newly available prey catfish individuals were fishing to analyze their where it has been introduced. Migrating spawning stomach content. Catfish disturbed 12% of the 1024 anadromous prey such as allis shad Alosa alosa could nocturnal spawning acts we heard, and this proportion represent this available and energy-rich food resource. increased to 37% among the 129 spawning acts when Here, we report an impressive catfish hunting behavior estimated with low-light camera recording. Stomach on shad spawning act in one of the main spawning content analyses on 251 large catfish individuals (body grounds in Europe (Garonne River, Southwest length [ 128 cm) caught in the same river stretch France). Shad spawning act consists of at least one revealed shad represented 88.5% of identified prey male and one female swimming side by side, trashing items in catfish diet. This work demonstrates that the water surface with their tail which, therefore, European catfish predation must be considered as a produces a splashing noise audible from the river significant factor of mortality of allis shad. In a context bank. The catfish hunting behavior on shad spawning 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 Handling Editor: Te´lesphore Sime-Ngando. European conservation plans of anadromous species. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10452-020-09811-8) con- Keywords Anadromous fish Á Diet Á Endangered tains supplementary material, which is available to authorized users. species Á Large non-native apex predator Á Mating S. Bouleˆtreau Á F. Aze´mar Á F. Santoul (&) Laboratoire Ecologie Fonctionnelle et Environnement, ´ Universite de Toulouse, CNRS, Toulouse, France Introduction e-mail: [email protected] T. Fauvel Migratory animals in search of food, new habitats or IMA, 1 rue de Donzac, 64101 Bayonne, France mates, concentrate in time and space, strongly expos- ing them to predators. The well-known annual migra- M. Laventure Á R. Delacour Á W. Bouyssonnie´ MIGADO, 18 Ter rue de la Garonne, 47520 Le Passage, tion of wildebeest (Connochaetes taurinus) through France 123 Author's personal copy Aquat Ecol the Serengeti triggers high densities of adult croco- recently in Brazil (Cunico and Vitule 2014; Cucher- diles (Crocodylus niloticus) when crossing the Mara ousset et al. 2018). In Southwestern France, the first River (Subalusky et al. 2017). The shoals of migrating introduction likely occurred during the 1980s (Sch- sardines (Sardinops sagax) along the east coast of lumberger et al. 2001). South Africa also known as ‘sardine runs’ concentrate Stable isotope analysis revealed that the diet of many associated predators such as the common some specialized European catfish individuals could dolphin (Delphinus capensis), the cape gannet (Morus reach up to 50% of marine prey in the Garonne River capensis) or the bottlenose dolphin (Tursiops adun- in Southwestern France (Syva¨ranta et al. 2009). More cus) (O’Donoghue et al. 2010). In freshwater ecosys- specifically, anadromous fish such as twait shad (Alosa tems, brown bears (Ursus arctos) and black bears fallax), thinlip grey mullet (Chelon ramada), sea (Ursus americanus) kill at least half of the returning lamprey (Petromyzon marinus) and Atlantic salmon adult Pacific salmons (Oncorhynchus spp.) that spawn (Salmo salar) have been detected by DNA metabar- in small streams in Alaska (Quinn et al. 2003). In coding techniques in European catfish feces or stom- South-Central Connecticut, double-crested cormorant ach contents (Libois et al. 2016; Guillerault et al. (Phalacrocorax auritus) are important predators for 2018; Ferreira et al. 2019). Fishermen have also alewife (Alosa pseudoharengus) (Dalton et al. 2009). reported some allis shad (Alosa alosa) individuals in Many fish species migrate between seawater and European catfish stomach contents. The allis shad freshwater to spawn. Most of these anadromous (Alosa alosa) is a member of the herring family, species are protected from fish predation during their Clupeidae. This anadromous fish can be historically upstream migration by their large adult body size. found along the northeastern Atlantic coast from Biological invasions have disrupted this rule, given Morocco to Norway (Baglinie`re et al. 2003). Adult that introduced predatory fish species are globally allis shad occurs mainly in shallow coastal water and larger than native fish species (Blanchet et al. 2010). estuaries, but, during the spawning migration, adults For instance, the introduced piscivorous blue catfish enter well upstream in some of the largest European (Ictalurus furcatus) mainly consume Alosa sp. during rivers, mainly in France, Spain and Portugal (Maitland their spawning run in the upper tidal freshwater and Hatton-Ellis 2003). The allis shad is now critically reaches of the Rappahannock River in Virginia, USA endangered over most of its range due to pollution, (MacAvoy et al. 2000). In western and southern overfishing and river fragmentation (Aprahamian et al. European freshwaters, the establishment of the large 2003). Further, its spawning migration is often limited non-native European catfish Silurus glanis also by obstacles to migration, such as waterfalls and man- exposes adult anadromous fish species to predation made dams and weirs. Moreover, predation-induced by increasing the threshold body size at which prey are mortality in rivers, though to be important, has never invulnerable to predation. The European catfish is been quantified. Here, we report the occurrence of a among the 20 largest freshwater fish in the world and is hunting behavior in the non-native European catfish the largest in Europe (Stone 2007; Bouleˆtreau and on spawning allis shad. Additionally, we quantify the Santoul 2016). The species can measure up to 2.7 m impact of European catfish predation on migrating total length (Bouleˆtreau and Santoul 2016), with adults allis shad in one of the main European spawning being at least twice larger than native predators (e.g., grounds in Southwestern France. Northern pike Esox lucius). The species is native from Eastern Europe. Its native distribution extends from Germany eastward through to Poland, up to Southern Methods Sweden, and down to Southern Turkey and Northern Iran through the Baltic States to Russia and to the Aral Study site Sea of Kazakhstan and Uzbekistan (Copp et al. 2009). Their extremely body size has resulted in making them The Garonne basin (Southwestern France) hosted the an increasingly popular target species for recreational largest allis shad population in Europe at the end of the anglers in Europe, resulting in their intentional twentieth century (Rougier et al. 2012). The 1400 m introductions into some Western and Southern Euro- long studied stretch is located in the tailrace of the pean countries, but also in China, Tunisia and more Golfech-Malause large-scale hydroelectric complex at 123 Author's personal copy Aquat Ecol about 270 km from the river mouth (Fig. 1b). The Shad spawning acts stretch is ended upstream by a dam equipped with a fish lift as fishway (44° 60 34.1700 N, 0° 510 12.5800 E) Allis shad spawning occurs at night during spring and a permanent video fish-counting to monitor fish months (from April to June with a peak at the end of upstream passages (Fig. 1a). The fishway is fit with a May). The typical spawning act consists of at least one fish trap that allows fish collection. In this stretch, the male and one female swimming side by side in circle river is channelized and approximately 100 m wide and thrashing the water surface with their tail (Acolas with a mean depth of 6 m. The stretch belongs to the et al. 2006). The splashing noise (35 dB at one meter) industrial area where passing and angling are prohib- can be heard from the riverbank (Chanseau et al. 2005; ited. The studied spawning ground (80 by 100 m Diep et al. 2016). Counting the number of splashes around) is located at the downstream part from the (auditory survey), i.e., the number of spawning acts stretch (44° 60 53.7500 N, 0° 500 19.7300 E).