Interpretation of geographic variation in size of American eel Anguilla rostrata elvers on the Atlantic coast of North America using their life history and otolith ageing

Abstract

Elvers of the American eel Anguilla rostrata (LeSueur) were collected from 6 estuaries ranging in location from Haiti to the U.S. Atlantic coast and north to Canada during the fishing season in 1995. Time of metamorphosis from leptocephalus to glass eel was determined from otolith daily growth increments, in which the increment width and strontium/calcium ratios changed drastically. Mean age of the leptocephalus at metamorphosis (T(m)) was 189 to 214 d, while age upon arrival at the estuaries (T(t)) was 220 to 284 d. Time from metamorphosis to arrival at the estuaries (T(t-m)) was 32 to 80 d. Faster-growing and earlier-metamorphosing leptocephali migrate to the mid-point of the sampling range, but slower-growing and delayed-metamorphosis leptocephali occur in both the southern and northern ranges. Duration of the glass eel phase was longer in the north than in the South, while glass eels grew faster in the south than in the north. Mean total length of elvers at entry to the estuaries increased significantly from 48 mm in the south to 60 mm in the north. Geographic variation in elver length was due to duration of the glass eel phase rather than timing of metamorphosis from leptocephalus to glass eel, because elver length was significantly positively correlated with T(t-m) (r = 0.79, p < 0.01) but not significantly correlated with T(m) (p > 0.05). Duration of the glass eel phase was influenced by the coastal oceanographic conditions.