ABSTRACT: Environmental history of the European eel Anguilla anguilla (L.) collected from Swedish brackish waters and lakes was studied by examining strontium (Sr) and calcium (Ca) in their otoliths with wavelength dispersive X-ray spectrometry on an electron microprobe. The Sr/Ca ratios in the otoliths changed with both ontogenetic development and salinity of the habitat. A peak Sr/Ca ratio of approximately 2 x 10^-2 was observed in the marine phase of the otoliths, corresponding to the period when a leptocephalus metamorphosed into a glass eel. The ratios decreased to 5.72 (± 0.32) x 10^-3 at yellow eel stage when the fish lived in brackish water and to 3.7 (± 0.20) x 10^-4 in fresh water. The ratios were significantly different between brackish and fresh water (p < 0.00001). Several relatively higher Sr bands were found in otoliths of eel from brackish waters but not in the eels from fresh water. Salinity probably influences Sr deposition more than does temperature or somatic growth rates.

KEY WORDS: European eel · Otolith · Strontium/calcium ratios · Elemental X-ray map · Environmental factor · Migratory history · Electron microprobe

Published in MEPS Vol. 149 (1997) on April 10
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997