Elver (Anguilla anguilla L.) stockings in a Swedish thermal effluent-recaptures, growth and body condition

Stockings of elvers (Anguilla anguilla L.) were made in 1982 and 1984 in a Swedish cooling water effluent area at the coast of the Baltic proper. The elvers were tagged using radioactive europium isotopes; recaptures were made by yearly samplings from 1983–1989. Détéction of eels tagged by this technique was found to be possible for at least 7 years after stocking. At the end of the study, 3.5 % and 1.3 %, respectively, of the stockings were recaptured in our own sampling programme. Growth of the introduced eels was faster than reported in studies on comparable populations. As high temperatures have a potential to change vital physiological functions, body condition, fat content and size distribution were studied in the stocking area, in two additional cooling water effluents, and in two reference areas along a salinity gradient from the Baltic to the northern Kattegat! where Atlantic waters have a major influence. Although there were indications of early sexual maturation in warm waters, the high survival of introduced eels, their tendency to stay in the stocking area, the fast growth and the positive effect on quality paramétérs such as fat content speaks in favour of an allocation of eel management to thermal discharge areas.