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Tunas make sharp descents and ascents around dawn and dusk called spike dives. We examine spike dives of 21 southern bluefin tuna (Thunnus maccoyii) implanted with archival tags in the Great Australian Bight. Using a new way to categorize this behavior, we show that spike dives are similar among all the fish in the study. The dive profiles are mirror images at dawn and dusk and are precisely timed with respect to sunrise and sunset. We analyze the possible reasons for spike dives, considering the timing of spike dives, the characteristic dive profile, and the tuna's magnetic habitat. In addition, we present anatomical evidence for elaboration of the pineal organ, which is light mediated and has been implicated in navigation in other vertebrates. The new evidence presented here leads us to suspect that spike dives represent a survey related to navigation.

Item Type:	Refereed Article
Keywords:	Migration . Pineal gland . Compass . Magnetic navigation . Polarized light . Archival tags
Research Division:	Biological Sciences
Research Group:	Zoology
Research Field:	Animal Behaviour
Objective Division:	Environment
Objective Group:	Ecosystem Assessment and Management
Objective Field:	Ecosystem Assessment and Management of Marine Environments
UTAS Author:	Willis, J (Mr Jay Willis)
UTAS Author:	Hobday, AJ (Dr Alistair Hobday)
ID Code:	62418
Year Published:	2009
Web of Science® Times Cited:	26
Deposited By:	Centre for Marine Science
Deposited On:	2010-03-12
Last Modified:	2010-05-12
Downloads:	0