Challenges for Diadromous Fishes in a Dynamic Global Environment

Abstract

<em>Abstract</em>.-The location of the spawning grounds of the three species of <em>Anguilla </em>that occur in New Zealand and Australia, shortfin eel <em>A. australis</em>, Australian longfin eel <em>A. dieffenbachii</em>, and Australian longfin eel (also known as speckled longfin eel) <em>A. reinhardtii</em>, are unknown. No larvae of New Zealand longfin eels have been collected, and too few shortfin eel and speckled longfin eel larvae have been collected to use conventional back-tracking of progressively smaller larvae to determine likely spawning areas. The limited larval material together with results from satellite tracking pop-up tags from New Zealand longfin eels indicate that spawning of all three species will be in the tropics, and possible areas were further demarcated by developing a Lagrangian trajectory model based on surface currents derived from hydrography, satellite altimetry, and wind stress. The initial model assumed passive drift of larvae, a third of the total time spent in near-surface layers, and arrival within the larval lifetimes indicated by ages of metamorphosing glass eels. The proportion of successful trajectories enabling arrival offshore of New Zealand or Australia was substantially improved by addition to the model of directed swimming of the larvae towards a destination. The model indicated that possible spawning areas for all three species would be in the northeast of New Caledonia, perhaps within the North Fiji basin between Vanuatu and Fiji. Spawning within this region is consistent with the locations of known larvae, probable migration routes, and the distribution of adult eels in both countries.