From the Lab Bigeye tuna dive deep with the moon CSIRO scientist
Karen Evans has tagged tunas, billfish, sharks, seabirds, seals
and whales from the tropics to Antarctica. She develops and
deploys tags, and analyses their data to see how top order
predators move, feed and behave. Karen led the data analysis and
reporting of a project that tagged 161 bigeye tuna with archival
tags and 269 with conventional (spaghetti) tags in the Coral
Sea. Sixty-six conventional tags and 17 archival tags were
returned, from fish that had travelled 10 to 8000 nautical miles
from where they were tagged. Daily fish positions estimated from
archived light levels and sea surface temperatures (from
satellite) showed most bigeye did not migrate long distances.
They spent their days 250–500 metres deep, their nights at less
than 200 m, and tolerated waters from 2.5–22°C. Some fish dived
deeper on the full moon. This wide-ranging diving behaviour
enables bigeye to locate scarce prey while minimising
competition with other tuna species