Oceanic migration routes and behaviour of the New Zealand longfin eel Anguilla dieffenbachii

Abstract

Delineating oceanic migration routes of adult anguillid eels is essential for characterising threats to this crucial stage in their reproductive life cycle. We tagged 20 female migrant (silver) New Zealand longfin eels Anguilla dieffenbachii with pop-up satellite archival tags, releasing 10 on the west coast of the North Island and 10 on the east coast of the South Island. Data retrieved from 12 of the tags deployed were used to reconstruct the migratory behaviour and pathways of the eels in the ocean. No tags reached their programmed release date, with the average deployment duration being 35.6 d (range 12-86 d). Of the 12 tags that returned data, 4 showed clear signs that they had been predated on, the first evidence of oceanic predation of this species. Eight eels commenced diel vertical migration following release, with eels occupying deeper water during daylight hours and shallower waters at night. Reconstruction of migratory pathways indicate an overall northerly trajectory from release sites, with some lateral movement also observed. Our study provides the first evidence of migrating eels from both the east and west coasts of New Zealand converging in a region of open ocean in the South Fiji Basin. This strengthens evidence for the hypothesised spawning location being situated somewhere between Fiji and New Caledonia. Future tagging efforts should focus on catchments with a direct ‘line of sight’ to the Fiji Basin (e.g. the Northland and Bay of Plenty regions) that minimise the time eels spend in the near coastal zone.