First use of archival transmitters to track migrating freshwater eels Anguilla dieffenbachii at sea

The spawning grounds of the New Zealand longfinned eel Anguilla dieffenbachii are unknown, but thought to be in the tropical region of the south Pacific Ocean. To determine whether pop-up tags could be used to provide information on the swimming speed and direction of migrating eels at sea, 4 female eels (7 600 to 11400 g) were equipped with archival pop-up tags that were preprogrammed to surface after either 2 or 3 mo. All 4 tags ascended successfully at straight-line distances ranging from 368 to 1000 km offshore of the east coast of South Island, New Zealand, These estimated migration pathways showed that the eels moved substantial distances along inshore areas before moving offshore and eastward. There was no evidence of the expected northeast movement to tropical waters, Average swimming speed of all eels ranged from 15.1 to 31.3 km d(-1), but there was limited evidence of diel vertical movement within the water column. The results indicated that pop-up tags have considerable potential in tracking the marine migrations of the larger species of Anguilla.