MEPS 286:261-267 (2005)  -  doi:10.3354/meps286261

Swimming depths of offshore migrating longfin eels Anguilla dieffenbachii

Donald Jellyman1,*, Katsumi Tsukamoto2

1National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand
2Ocean Research Institute, University of Tokyo, Minamidai, Nakano-ku, Tokyo 164-8639, Japan

ABSTRACT: Pop-up tags were attached to 10 migratory female longfin eels Anguilla dieffenbachii, ranging in size from 6000 to 10550 g. Tags were scheduled to ascend at monthly intervals, commencing 3 mo after release. A combination of eel mortality, tag failure, and premature detachment meant that limited data were retrieved. The 3 eels where tags remained attached for 25 d or more generally swam too deep for light reception and hence geolocation estimates, meaning that no tracks of their swimming routes could be determined; all 3 eels showed diel vertical movements with 1 fish always returning to near surface depths (1 to 10 m), while the other 2 tended to ascend to 150-200 m but frequently dived to >600 m; maximum recorded depth was 980 m. It was assumed that such extensive diel movement was in response to predator avoidance and also to thermoregulation as eels often spent time in 5 to 6°C water. The tag from one of these eels commenced transmissions at a location 700 km east of New Caledonia.This is the first evidence that this species moves to the tropics during spawning migrations.

KEY WORDS: Freshwater eel · Anguilla dieffenbachii · Swimming depth · Satellite

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