Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 +/- 1.09 parts per thousand,) than for those from the lake (0.71 +/- 0.89 parts per thousand,). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase.