Elemental composition of otoliths as a discriminator of life stage and growth habitat of the European eel, Anguilla anguilla

Abstract

The hypothesis that elemental composition of otoliths of the eel (Anguilla spp.) changes with life stage and growth habitat was tested in the present study. The minor elements Cl, Na, K, Mg, Ca, Sr and P in otoliths of European eels (Anguilla anguilla) were examined by using an Electron Probe Microanalyser (EPMA) equipped with wavelength dispersive spectrometers (Cameca SX-50). Yellow-stage eels were collected from coastal waters and lakes of Sweden in 1987, 1988, 1991, and 1994, with ages ranging from 5 to 18 years old. Strontium maps and profiles of Sr : Ca ratio, as well as the elver check in otoliths, were used to classify life history stages of the eels as leptocephalus, and freshwater- and seawater-resident yellow eels. Canonical score plots of the otolith elemental compositions of the freshwater-resident yellow eel were completely separated from those of leptocephalus and seawater-resident yellow eel, but the latter two partially overlapped. Strontium is the primary component in determining the discrimination, but the nutrient-related (S and P), and the physiologically controlled elements (Na and Cl), may also play an important role in the discrimination. These results indicate that multiple-elemental information can provide additional insight into the migratory environmental history of diadromous fishes.