Testing Three Methods to Reinforce Eel Population in a Southern European River (Oria, Spain), 2011-2013

The presence of obstacles restricts the eel distribution to the lower part of the Oria river (NE Spain). Thus, three different ways of moving eels upstream within the same basin were tested to encourage  the entire eel habitat colonization in the river. Firstly, in June 2011, the migration of 5.1 kgs of elvers from a trap located in the tidal limit to a tributary upstream was assisted. Secondly, in January 2012, 3.2 kg of wild glass eel fished in the estuary were transported directly to the upper part of the Oria´s main course. Finally, 1.7 kg of glass eels cultured for 45 days were released in an upper tributary in March 2012

All the release points had good water and habitat quality and released eels will be able to migrate downstream during flooding in autumn once they mature. Electrofishing surveys have been made at the beginning of the first summer after the release and then, yearly in September. The recapture rate has remained constant in the elvers from the trap, and has decreased with the other two methods. All the released eels were able to grow, although grow rate and condition factor of cultured glass eels were the lowest.