Why do young Pacific bluefin tuna repeatedly dive to depths through the thermocline?
Article first published online: 1 FEB 2007
Volume 73, Issue 1, pages 98–106, February 2007
How to Cite
KITAGAWA, T., KIMURA, S., NAKATA, H. and YAMADA, H. (2007), Why do young Pacific bluefin tuna repeatedly dive to depths through the thermocline?. Fisheries Science, 73: 98–106. doi: 10.1111/j.1444-2906.2007.01307.x
- Issue published online: 1 FEB 2007
- Article first published online: 1 FEB 2007
- Received 1 February 2006. Accepted 7 September 2006.
- archival tag;
- behavioral thermoregulation;
- feeding events;
- Pacific bluefin tuna;
- repeated dive
ABSTRACT: Young Pacific bluefin tuna Thunnus orientalis with archival tags were released in the East China Sea. Time-series data for depth, and ambient and peritoneal temperatures for nine fish, recorded every 128 s, were analyzed. Our objectives were to describe monthly changes in diving patterns in relation to the ambient thermal structure and the occurrence of feeding events during March–June, and to discuss possible reasons why bluefin tuna repeatedly dived to depths below the thermocline in terms of their thermoconservation mechanisms. It was found that the fish repeatedly dived through the thermocline at intervals of 1.2 h on average, and the dive frequency was high during March–May. However, the dive frequency and periodicity decreased in June, when the gradient became steeper. In contrast, feeding events increased in June. These results indicate that from March to May, bluefin tuna repeatedly dive because food biomass is inadequate at the surface, and they stop undertaking repeated dives in June when food becomes more readily available at the surface, in addition to low visibility caused by low solar radiation. Further, the range of heat transfer times for these fish was so long that their peritoneal temperature was probably maintained by engaging in brief dives. The periodicity of dives may lead to a lower fluctuation in the peritoneal temperature, suggesting that the dives are a kind of behavioral thermoregulation.