Stable isotopes from individual glass eels (Trueman 2019)

OPLS-DA scores plots showing clustering of glass eels obtained by (A) positive and (B) negative ionization mode (ZITEK 2019)

Glass eel otolith before grinding (ZITEK 2019)

Juvenile eel head (ZITEK 2019)

Glass eel otolith after grinding (ZITEK 2019)

Glass eel otoliths (ZITEK 2019)

Determining the potential of otolith and tissue microchemistry for the traceability of glass eels

Project duration: 07/2017 – 05/2019
Project partners: BOKU Vienna, University of Southampton
Contact: Florian Stein, Director of Scientific Operations, f.stein@SustainableEelGroup.org

Download project report here!

Export of European eel from and into the EU is suspended since December 2010 and EU regulations set a clear framework and therefore demands the identification of origin and traceability of all live eels. Two major factors impede the traceability of live traded European glass eels across Europe and beyond: (1) The species range of A. anguilla exceeds the borders of European Union and consequently eels of different origin cannot be distinguished by genetics. (2) Illegal trade of glass eel from Europe to Asia has recently been identified as one of the potential major threats for the species survival and is estimated to account for 30-50% of the declared European glass eel catches. In addition, countries neighboring the EU, increasingly export European eels since 2010. It is uncertain if these exports from non-EU countries originate from their territories, or if shipments include eels of EU origin.

Conclusions

The project provides the following conclusions:

• Sr/Ca, Rb/Ca, S/Ca, Mg/Ca and Sr/Ba ⁸⁷Sr/⁸⁶Sr isotope ratio in eel bodies proved to be good geographical discriminators between UK, French and Spanish samples, as they directly reflect the habitat conditions.

• Otolith data could not contribute to a differentiation, as the habitat information was obviously not sufficiently incorporated in the otoliths to be detectable by LA-ICP-MS with the chosen setup.

• Non-targeted molecular screening could be a valuable complementary method, when a stable relation to the geographic location can be established.

• Stable isotope compositions (d13C, d15N, d34S) of eel muscle tissues were able to differentiate among sample origins, with d34S values in particular discriminating among sites.

Recommendations

It is recommended that:

• Elemental and stable isotopic patterns (d13C, d15N, d34S, ⁸⁷Sr/⁸⁶Sr) of eel bodies together with metabolomic fingerprints need to be further explored for the geographic differentiation of glass eels.

• Reference data specific to the year and estuary in question are likely to be required for any applied assignment