Glass eel (Anguilla anguilla) predation risk by European sea bass (Dicentrarchus labrax) in the lab: Have VIE-tagged glass eels an increased predation risk? : how long can glass eels be detected in the stomach of a Sea bass?

A.B. Griffioen, T. Wilkes, W. Janssen, T. Menke

Research output: Book/ReportReportProfessional

Abstract

The European eel (Anguilla anguilla L.) is an economic important species and is listed on the IUCN red list as critically endangered. Nonetheless, each year between late winter (February) and late spring (May) glass eels arrive at the various coastal areas attempting to migrate to freshwater habitat. As part of the statutory tasks (WOT) a yearly index of glass eels arriving at the sluices at Den Oever was created since 1938. The program consists of a monitoring with liftnets and traps and is commissioned by Wageningen Marine Research (WMR). In addition, WMR also equips glass eels with a Visible Implant Elastomer tag to determine abundance and differences in retention time between years since 2019 using (batch) mark- and recapture methods. However, effects of tagging in relation to predation risk are unknown. Tagged glass eels might have an increased risk for predation, which in turn would influence abundance and retention time estimates. This study aims to determine differences in predation risk when glass eels are equipped with a VIE tag and exposed to European sea bass (Dicentrarchus labrax). Also, this study aims to determine the feasibility of stomach content analysis of predatory fish for future field studies on predation of glass eels near barriers. To answer both questions a laboratory experiment was conducted using marked (red and blue) and unmarked glass eels which were exposed to sea bass for a 2-hour trial. If at least one glass eel was eaten, stomach content was analyzed by a hand pump. 48% of the trials showed successful predation and 13% showed clear attempts of predation but failed to eat glass eels. The other sea bass (39%) waited significantly longer to show some activity, and they moved significantly less. The study showed that no differences in predation risk for marked glass eels by European sea bass. Also, no difference was found in predation between red and blue marked glass eels. Stomach content analysis showed intact glass eel bodies after ending the 2-hour trial and glass eels could be clearly identified after 4 hours and parts of glass eels were found after 16 hours. This study shows that mark-recapture studies are not influenced by an increased predation risk of marked glass eels. Also, if European sea bass predates on glass eels in the field, it can be detected using a hand pump in field studies if conducted within 4-6 hours after predation.
Original languageEnglish
Place of PublicationIJmuiden
PublisherStichting Wageningen Research, Centre for Fisheries Research (CVO)
Number of pages32
DOIs
Publication statusPublished - 2 Dec 2020

Publication series

NameCVO report
No.20.027

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