Furthermore, the European catfish is known to display individual trophic specialisation through foraging on terrestrial birds by intentional beaching [11]. Predators also consist of humans for hunting/fishing.

EcoLab, Université de Toulouse, CNRS, Toulouse, France, Roles The aim of this study is to assess the risk for the Atlantic salmon to be predated by the European catfish inside an anthropized system. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. This diversion-type hydropower facility is the first barrier for upstream migration of anadromous species in the Garonne River. By contrast, catfish preferentially passed nightly between 11pm and 9am (median value at 4am). Methodology, First European catfish passages at the video fish-counting station occurred in 1995, with three individuals. The Atlantic salmon, considered as an endangered species in Western Europe, was eliminated in the mid 1900s from many large, heavily anthropized and fragmented rivers [12,13], such as the River Garonne (Southwest France).

In this context, human activities that affect fish movement may increase the exposure of Atlantic salmon to predators. Large adult salmon (mean 80 cm total length), compare to generally smaller freshwater fish prey, could be preferentially selected by large catfish. From 2004 to 2008, the frequency downstream passages by catfish was low. on salmon inside the fishway during the 2016 spawning period migration. Over-fishing is a great problem for the Atlantic Salmon. This number progressively increased until 2004 to reach an average of 590 (±232 SD) individuals per year during subsequent years.

Our understanding of the rates of Atlantic salmon (Salmo salar L.) predation and survival throughout the Miramichi River, estuary and bay has increased through recent studies. Data curation,

broad scope, and wide readership – a perfect fit for your research every time. Supervision, In 2014, 2015 and 2016, a higher proportion of European catfish were observed at the end of the day, between 5pm and 10pm (Fig 4B). Multiple stressors are known to interact synergistically to amplify the individual effects of global change drivers on species and ecosystems [23,24,25].

This invulnerability has disappeared in Western Europe with the introduction of a new freshwater predator, the European catfish (Silurus glanis). Methodology, Affiliation Yes No, Is the Subject Area "Europe" applicable to this article?

Here, the anthropization of the river provides a local opportunity for European catfish to exploit migrating Atlantic salmon. Moreover, intraspecific variation in trophic specialization might explain the ability of introduced species to establish populations.

At regular intervals (depending on fish passage frequency), fish are trapped and concentrated into a 3.3-m3 tank. A total of 35 European catfish were captured in the transfer canal in April 2015 (n = 10) and in April 2016 (n = 25) to be tagged in order to monitor their presence inside the fishway. Located in southwestern France, the Garonne River runs over 580 km from its source in the Pyrenees to the Atlantic Ocean. The Golfech–Malause hydroelectric complex was built in 1971 on the Garonne River (southwestern France) about 270 km from the river mouth (0°55’22.3”E; 44°06’37.6”N), downstream from the confluence with the Tarn River (Fig 1; see [15] for more details). Data curation, Introductions of large-bodied predator fish that forage at the apex of food webs are known to impact native fish populations and modify prey assemblages as well as food web structure [3,4]. Copyright © 2005 Elsevier B.V. All rights reserved. To this end, we hypothesized that some specialized catfish individuals could adapt their foraging behaviour to this restricted and anthropized spatial environment leading to Atlantic salmon predation in the fishway.

Acoustic camera records performed from April 4th to May 26th 2016 (51 days) at the exit of the fishway showed that there were often between one and six European catfish individuals waiting at the exit of the transfer canal. When adult, the easiest way of identifying them is by the black spots predominantly above the, Fry and parr have been said to be territorial, but evidence showing that they guard territories is inconclusive.

While they may occasionally be aggressive towards each other, the, Young salmon begin a feeding response within a few days. The remaining 14 salmon—unobserved with the acoustic camera (35%)—were predated by European catfish inside the transfer canal between the video station and the exit. For more information about PLOS Subject Areas, click Create your own unique website with customizable templates. Writing – original draft, Egg and juvenile survival is dependent on habitat quality as Atlantic salmon are sensitive to ecological change. The number of incursions they performed, the time of their incursions and the cumulative time they spent inside during the year of their release differed between individuals, with annual incursion number ranging from one to 21 (Fig 5B), annual number of detections ranging from 179 to 2012 (Fig 5C) and cumulative annual time inside ranging from 10 hours to 10 days (Fig 5D). The continuous occurrence of several catfish individuals at the exit of the fishway suggests that predators occupy this strategic location to capture other fish prey. Large individuals can measure over 2.7 m total length and weigh 130 kg [7]. Funding acquisition,

Data Availability: All relevant data are within the paper and its Supporting Information files. No, Is the Subject Area "Animal migration" applicable to this article? Detections occurred from April 20th to July 14th, 2015 and from April 29th to August 16th, 2016.

Fish are attracted into a 9-m long, 2.5-m wide and 1.5–4.5-m deep holding pool. Largely introduced in the 1970s’ the European catfish Silurus glanis is now widespread in western and southern European freshwaters where it has established self-sustaining populations in most large rivers [6]. Click through the PLOS taxonomy to find articles in your field. Timings of passages of Atlantic salmon (dark grey) and European catfish (light grey) at the fishway in the River Garonne: (a) annual net number of fish counted at the video fish-counting station since its installation in 1993; (b) month distribution (in %) of over the period 1993–2016.
During this period, a total of 187 European catfish were observed exiting from the transfer canal and 86 coming back into the fishway. Nearly all Atlantic salmon sold in the United States is farm raised, as catching and selling wild Atlantic salmon is prohibited under U.S. regulations. Investigation, For more information about PLOS Subject Areas, click No, Is the Subject Area "Marine fish" applicable to this article?

The same authors demonstrated, from electromyogram biotelemetry records, that there is considerable individual variability in diel activity depending on different individual behaviour and ability to use energy reserves [21]. With its large gape size, the European catfish is a potential predator to many if not all native fishes, including anadromous species so that native species would no longer benefit from the size-refuge that protected them against native top-predators (e.g., pike; [8]). Conceptualization, 23 catfish (66%) have performed only one annual incursion inside the transfer canal staying inside from less than 1 minute to 17.6 hours (Fig 5A). Rivers of the coast of Maine, plus southern New Brunswick and much of mainland Nova Scotia saw runs drop precipitously, and even disappear.

Investigation, Despite conservation and rehabilitation plans, populations of this species are dramatically declining due to human impacts such as habitat fragmentation, overfishing and water pollution. PLOS ONE promises fair, rigorous peer review, here.

This does not alter our adherence to PLOS ONE policies on sharing data and materials. While they mature, they take on a silver blue sheen. Diet plasticity is a common phenomenon in top predators with high-energy requirements and the ability to learn to utilize new resources. https://doi.org/10.1016/j.fishres.2005.06.015. Conceptualization, The migration period of salmon is only slightly earlier with 78% of salmon passing between March and July. The main causes of global Salmonid decline are well identified. Discover a faster, simpler path to publishing in a high-quality journal. Investigation, A well-known example is given by the introduction of the Nile perch in African lakes that negatively impacted cichlid populations and the food web through top-down effects [5]. Years 2007 and 2012 exhibited the highest annual numbers of European catfish with 1134 and 956 individuals respectively (Fig 2A). Some of the most common predators that eat salmon include bears, otters, eagles, osprey, sharks and humans.

https://doi.org/10.1371/journal.pone.0196046.g001. Fish were transferred to a tank of clean water to recover from anaesthesia and released just outside the upstream exit of the transfer canal.

Funding acquisition, The annual number of returning adult Atlantic salmon averaged 166 (±131 SD), ranging from a minimum of 45 individuals in 2005 to a maximum of 599 individuals in 2001 (Fig 2A). Yes

Moreover, specific morphological characteristics of Atlantic salmon and European catfish (body size and form, catfish head shape and salmon dorsal fin) can allow easily and undoubtedly distinguishing these two species from others. The Golfech power plant structure was equipped in 1987 with a fish lift on the right bank of the tailrace. MIGADO, Saint-Orens-de-Gameville, France, Roles Habitat fragmentation, habitat alteration, acidification and overexploitation seriously threaten populations of species such as the Atlantic salmon [1,2]. The colouration of young Atlantic salmon does not resemble their adult stage. Here we report how adults of Atlantic salmon are predated in the fishway of a large river of SW France, where the delayed and narrow passage created by the structure increases the probability of predator-prey encounter. Conceptualization, This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Yes Based on analyses of the fish stomach contents, lesser sandeel (Ammodytes marinus) was found to be the dominant prey, while no remains of Atlantic salmon, including otoliths, were found.



This number of Atlantic salmon exhibited a slight peak between 1999 and 2002. During these times, the Atlantic salmon are very susceptible to predation. Our results suggest that a few specialized catfish individuals adapted their hunting behaviour to such prey, including their presence synchronized with that of salmon (i.e, more occurrences by the end of the day).