Dispersal pattern of glass eel stage of Anguilla australis revealed by otolith growth increments

Abstract

Glass eels of the Australasian shortfin eel Anguilla australis (Richardson 1841) were col- lected from 6 Australian and 2 New Zealand estuaries. Their ages were estimated by counting daily growth increments in the otoliths. According to mean size and age at capture, the glass eels were classified into a northern Australia group or a southern Australia and New Zealand group. The mean length of glass eels increased from 47.6 ± 2.11 mm in northern estuaries to 59.2 ± 3.61 mm in the south. The mean age of glass eels at capture was significantly lower in the north (214 ± 14.6 to 223 ± 17.7 d) than in the south (243 ± 19.7 to 261 ± 22.4 d) (p < 0.05). In contrast, the otolith growth rate was greater in the north than in the south. The dramatic increase in increment width and the decline of the Sr:Ca ratios in otoliths were used to determine the timing of metamorphosis from lep- tocephalus to glass eel stage. The mean ages of leptocephali at metamorphosis were significantly lower in the north (160 ± 14.2 to 161 ± 12.6 d) than in the south (168 ± 14.5 to 189 ± 16.9 d), indicating that faster-growing and earlier-metamorphosed leptocephali recruited to northern Australia and slow-growing and late-metamorphosed leptocephali recruited to southern Australia and New Zealand. In addition, based on current direction and the similarity in age of leptocephali at metamor- phosis, age at capture and the period between metamorphosis and estuarine arrival, New Zealand glass eels are unlikely to be transported across Tasman Sea from southern Australia by the East Aus- tralian Current, and must reach their destination via a different route(s).