MEPS 233:217-229 (2002)  -  doi:10.3354/meps233217

ABSTRACT: The environmental history of American eels Anguilla rostrata from the East River, Nova Scotia, was investigated by electron microprobe analysis of the Sr:Ca ratio along transects of the eel otolith. The mean (±SD) Sr:Ca ratio in the otoliths of juvenile American eels was 5.42 x 10^-3 ± 1.22 x 10^-3 at the elver check and decreased to 2.38 x 10^-3 ± 0.99 × 10^-3 at the first annulus for eels that migrated directly into the river but increased to 7.28 x 10^-3 ± 1.09 x 10^-3 for eels that had remained in the estuary for 1 yr or more before entering the river. At the otolith edge, Sr:Ca ratios of 4.0 x 10^-3 or less indicated freshwater residence and ratios of 5.0 x 10^-3 or more indicated estuarine residence. Four distinct but interrelated behavioural groups were identified by the temporal changes in Sr:Ca ratios in their otoliths: (1) entrance into freshwater as an elver, (2) coastal or estuarine residence for 1 yr or more before entering freshwater, and, after entering freshwater, (3) continuous freshwater residence until the silver eel stage and (4) freshwater residence for 1 yr or more before engaging in periodic, seasonal movements between estuary and freshwater until the silver eel stage. Small (<70 mm total length), highly pigmented elvers that arrived early in the elver run were confirmed as slow growing age-1 juvenile eels. Juvenile eels that remained 1 yr or more in the estuary before entering the river contributed to the production of silver eels to a relatively greater extent than did elvers that entered the river during the year of continental arrival.

KEY WORDS: American eel · Otolith · Strontium:calcium ratio · Environmental history