Oceanic migration routes and behaviour of the New Zealand longfin eel <i>Anguilla dieffenbachii</i>

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

First observations of spawning nests in the pouched lamprey (Geotria australis)

The pouched lamprey, Geotria australis, one of four Southern Hemisphere lamprey species, is New Zealand's only freshwater representative of the agnathans. In contrast to Northern Hemisphere lamprey species, the reproductive ecology of Southern Hemisphere lamprey species is poorly understood with no documented nest sites or spawning behaviours. In the present study we utilised PIT tags to track migratory adult G. australis to locate spawning sites. Across two years, six cryptic nest sites were discovered, each containing eggs and a single male and female lamprey. The post-spawning pairs were all located underneath large boulders with the eggs forming a coagulated cluster that adhered to the underside of the boulder. Both the male and female lamprey survived spawning for over 105 days. The observed spawning nests highlight a substantial divergence in the reproductive behaviour between Northern and Southern Hemisphere lampreys, as the present observations of G. australis are the first that support clustered cryptic egg deposition and an extended time to mortality post-spawning. This study offers the first insights to the long-standing mystery of Southern Hemisphere lamprey reproduction.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Tracking anguillid eels: five decades of telemetry-based research

Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic spatial ecology of anguillid eels. Herein we review 105 studies published between 1972 and 2016 that used a variety of telemetry technologies to study the movements of eels in a variety of habitats. Eight anguillid species have been tracked in three main geographical locations: Western Europe, the north-eastern part of North America and Australasia. Telemetry has proven to be an effective method for determining patterns of yellow eel movements in continental waters. It has also been used extensively to investigate the migratory behaviour of maturing eels as they leave fresh water to reach the sea. Among recent findings is the observation that downstream migration in continental waters is quite discontinuous, characterised by extended stopovers. Reconstructed migration routes in the open ocean obtained from satellite tags have provided indications of spawning areas, extensive vertical migrations and initial clues about the orientation mechanisms at sea. Telemetry studies have also revealed apparent evidence of predation by marine mammals and fish at sea, suggesting a significant natural source of mortality during the eel spawning migration. Finally, we discuss some limitations of telemetry technology and future directions, as well as associated challenges, to the developing field of eel spatial ecology.</jats:p