Distribution and early life-history characteristics of anguillid leptocephali in the western South Pacific

Abstract

Freshwater eels are important fisheries species in parts of the western South Pacific, but little is known about their oceanic early life history or spawning areas. The age, growth, morphology and geographic distribution of five species of genetically identified anguillid leptocephali collected in 1995, 2000 and 2005 were compared. The sizes and ages of the leptocephali collected, Anguilla australis (n = 18), Anguilla marmorata (n = 15), Anguilla reinhardtii (n = 12), Anguilla megastoma (n = 2) and Anguilla obscura (n = 1), ranged from 19.0 to 50.9 mm and from 25 to 155 days, respectively. Leptocephali were mostly collected in the South Equatorial Current region. The total myomere ranges overlapped among species, but anodorsal myomere numbers clearly divided shortfinned and longfinned eels. The myomere ranges of the leptocephali were similar to the reported ranges of the numbers of vertebrae in adults. Larval growth rates suggested that the temperate species A. australis had slightly slower growth than the tropical species A. reinhardtii. The present study suggests that both temperate and tropical anguillid eels use the South Equatorial Current region for spawning and larval development, although some species might have different early life parameters and migration routes to their recruitment areas.

The ecology of oceanic dispersal and survival of anguillid leptocephali

“…Jellyman and Bowen (2009) found estimated spawning areas that were generally consistent with the larval catch data (Kuroki et al 2008) or tagging data (Jellyman and Tsukamoto 2010), but including a component of larval swimming (10 or 15 cm·s −1 ) was required to achieve those results. A larval transport modelling study was also conducted to evaluate the possible spawning locations of four species of anguillid eels in the western Indian Ocean region (Pous et al 2010).…”

“…Larval catches or silver eel tagging studies indicate that in addition to A. rostrata, the eels of A. japonica, A. marmorata, A. australis, A. reinhardtii, and A. dieffenbachii also make long migrations to offshore spawning areas (Kuroki et al 2008;Aoyama 2009;Jellyman and Tsukamoto 2010), and therefore their larvae have a long dispersal stage.…”

“…Japanese scientists then discovered the spawning area of A. japonica in 1991 (Tsukamoto 1992) after smaller and smaller larvae were collected farther offshore . These surveys expanded out across the Indo-Pacific (Aoyama et al 2003(Aoyama et al , 2007Kuroki et al 2006) with evidence of offshore spawning by eels in the western South Pacific being found (Kuroki et al 2008;Aoyama 2009) and local spawning by eels in the Indonesian seas being discovered (Aoyama et al 2003). These collections and genetic or morphological information about anguillid population structures (Minegishi et al 2008;Watanabe et al 2008Watanabe et al , 2011 and silver eel tagging studies (Schabetsberger et al 2015;Jellyman and Tsukamoto 2010) led to ideas about the locations of Indo-Pacific anguillid spawning areas ( Fig.…”

“…Some information has provided clues about where spawning occurs and how the larvae would be dispersed. Small leptocephali (20-34 mm) were collected of A. australis and A. reinhartii south of the Solomon Islands, a couple of small A. marmorata leptocephali (19 and 25 mm) have been collected to the east, and 24 unidentified small anguillid larvae (ϳ10 mm) were caught just northeast of Fiji (Kuroki et al 2008). The sizes of these larvae indicate that there are spawning areas in the region northeast of New Caledonia and north of Fiji.…”

“…There is evidence that some species in the western South Pacific make long migrations (Kuroki et al 2008;Jellyman and Tsukamoto 2010), but also that some tropical anguillids in the central Indonesian Seas spawn after much shorter migrations (Aoyama et al 2003). Anguillids in the western South Pacific, such as the two subspecies of Anguilla australis from Australia and New Zealand, the New Zealand longfin eel (Anguilla dieffenbachii) and the Australian longfin eel (Anguilla reinhartii), migrate far offshore to spawn in the South Equatorial Current according to collections of their larvae (Jellyman 2003;Kuroki et al 2008;Aoyama 2009) or data from satellite pop-up tagging studies of migrating silver eels (Jellyman and Tsukamoto 2010). There is also evidence about the location of a separate tropical eel spawning area in the western South Pacific from tagging studies (Schabetsberger et al 2015), and larval collections have indicated there is an anguillid spawning area in the eastern Indian Ocean (Jespersen 1942;Aoyama et al 2007).…”