Role of marine larval duration and growth rate of glass eels in determining the distribution of Anguilla reinhardtii and A. australis on Australian eastern coasts

Abstract

The differences in geographical distribution between Anguilla reinhardtii and A. australis on the eastern coast of Australia can be understood by comparing otolith growth increments and microchemistry, the ages between species of the eels at metamorphosis from leptocephalus to glass eels and the ages of glass eels at estuarine arrival. The ages at metamorphosis were determined from where the increment width dramatically increased and the Sr/Ca ratio dropped. The mean age (± s.d.) of A. reinhardtii (n = 176) at metamorphosis was 144.5 estuarine arrival was182.7 ± 16.3 days. For A. australis (n = 150) it was 173.7 ± 20.5 days and 229.2 ± 29.4 days, respectively. The differences in age between species were significantly larger than the annual and seasonal variations within species. Australian eels are believed to spawn in the tropical oceans and larval eels drift in the South Equatorial Current to eastern Australia. The younger ages at estuarine arrival of A. reinhardtii suggest that the spawning grounds of this species lie closer to Australia than those of A. australis. In addition, the mean total length at recruitment of A. reinhardtii (49.9 ± 2.0 mm) was significantly smaller than for A. australis (54.6 ± 5.4 mm) (t = 3.8, P < 0.01). However, the growth rates of A. reinhardtii (0.25 than for A. australis (0.23 ± 0.022 mm/d) (t = 7.6, P < 0.01). The smaller sizes of A. reinhardtii at recruitment were likely due to the shorter marine larval period and faster growth rate compared with A. australis. The duration of the marine larval period and growth rate may be the principal factors in determining the geographical distribution of both A. reinhardtii, which tend to occur in tropical-subtropical waters, and A. australis, which predominate in more temperate waters.