Comparison of early life history between New Zealand temperate eels and Pacific tropical eels revealed by otolith microstructure and microchemistry

Abstract

Otolith microstructure and microchemistry were examined in the glass eels of 5 species of Anguilla to compare the early life histories among the New Zealand temperate eels A. dieffenbachii and A. australis, and 3 species of tropical eels (A. bicolor pacifica, A. marmorata and A. celebesensis) collected in Indonesia and the Philippines. The ontogenetic patterns of fluctuation in increment widths and changes in otolith Sr:Ca ratios were similar in all species examined. They all showed an abrupt increase in increment width and a sharp drop in Sr:Ca ratio, suggesting the onset of metamorphosis from leptocephalus to glass eel. However, age at metamorphosis was different among the 5 species, as was age at recruitment to estuary (average ± SD), which was 297 ± 25.3 d in A. dieffenbachii, 268 ± 31.3 d in A. australis, 195 ± 25.8 d in A. bicolor pacifica, 170 ± 15.9 d in A. marmorata and 116 ± 17.7 d in A. celebesensis. Ages at metamorphosis and recruitment showed a linear relationship in all 5 species, and both of these ages were greater for the New Zealand temperate species than for the tropical eels. A. dieffenbachii recruited to freshwater habitats at the largest size and after the longest larval duration of any species of Anguilla ever reported. This suggests that in New Zealand A. dieffenbachii spawns at a location where their leptocephali take longer to reach their freshwater habitat than A. australis. This is in contradiction to speculation that A. dieffenbachii spawns, closer to New Zealand than A. australis, based on the more advanced stage of gonadal maturation that has been observed in the silver eels of the former species.