Does tagging transparent fish increase predation risk? A laboratory study with glass eel (Anguilla anguilla) and sea bass (Dicentrarchus labrax)

Abstract

Barriers in the estuaries of the rivers prevent the immigration of glass eels (Anguilla anguilla) arriving on the European coast every spring. This leads to an unnatural accumulation of migrating glass eels below the barriers, and this may lead to additional losses in glass eels by piscivorous fish. The proportion of predation losses can be estimated using mark-recapture techniques and abundance estimates in combination with stomach content analysis of piscivorous fish. Nonetheless, whether tagging transparent glass eels increases predation risk and what the digestion rate of glass eel is in piscivorous fish are unknown. This study aimed to determine whether there is an increased predation risk for tagged glass eel; it also studies glass eel digestion status in piscivorous fish after appointed time frames. A laboratory experiment with 48 trials was conducted. Tagged (visible implanted elastomer, VIE) and untagged glass eels were exposed to small (19.1-24.4 cm) and large (31.9-43.5 cm) sea bass (Dicentrarchus labrax) during a 2 h trial. In 48% of the trials, successful predation was present and 13% showed clear predation attempts in which bass did not capture glass eels. No significant difference was found in predation rate between tagged and untagged glass eels and between red and blue tagged glass eels. Large sea bass predated more, but all sizes consumed glass eel under laboratory conditions. Stomach content analysis showed intact glass eel bodies 4-6 h after ending the 2 h trial and parts of glass eel bodies up to 16-18 h. This study showed that tagging does not increase predation in mark-recapture studies using VIE-tags in transparent glass eel.It also shows that the proportion of predation in relation to local glass eel abundance can be estimated if stomach content analysis is conducted within 4-6 h after predation.

Glass eel migration in an urbanized catchment: an integral bottleneck assessment using mark-recapture

“…Inland barriers without efficient fish passage could result in prolonged glass eel accumulations. Although limited information is available, predation and loss of condition, due to multiple unsuccessful attempts, might occur at these sites [ 58 – 60 ]. If glass eels fail to migrate to suitable habitats in the hinterland, glass eel might settle in the NSC.…”

Research and Monitoring plan Fish Migration River (FMR)

“…Mark-recapture techniques are present in various forms and differences among these methods include group (mass) or individual marking, tag retention and the necessity to kill glass eels to identify recaptures. Examples are methods such as alizarin red S (Kullmann et al 2017, Kullmann et al 2018, Diekmann et al 2019, oxytetracycline (Simon and Dörner 2005), vital dyes (Briand et al 2005), coded wire tags (Simon and Dörner 2005), PIT tags ) and visible implant elastomer (VIE) tags (Imbert et al 2007, Griffioen et al 2022a) are all used in the field for various purposes. To answer the research questions of passage success (Q2) and bottleneck analysis (Q3), marking method that can discriminate between groups, affecting neither behaviour nor survival, are preferred.…”

Survival, growth and tag retention of juvenile European eel (Anguilla anguilla L.) with implanted 12 mm passive integrated transponder tags and acoustic tags

“…Small eels have been successfully tagged with visible implant elastomers (VIE) (Simon & Dörner, 2011) and coded wire tags (CWTs) (Thomassen et al, 2000;Jepsen et al 2010). Griffioen et al (2022) found that marking glass eels with VIE did not lead to increased predation.…”

“…Griffioen et al . ( 2022 ) found that marking glass eels with VIE did not lead to increased predation. Although these methods work well, their use is limited to situations where the eels are recaptured.…”