You won’t believe how this little chap has grown

22 years ago, a team from the Commission for the Conservation of Southern Bluefin Tuna (let’s call them the CCSBT!) first met a bluefin tuna, which they nicknamed Bluey. Bluey was caught and tagged in the Great Australian Bight in 1993, at which point she was just a juvenile at about two years old.

Juvenile Bluefin Tuna

Juvenile SBTs are quite small and easy to handle (see above), which means it’s possible to tag and release as many as 11,000 tuna in a session.

That was then, and this is now.

Bluey was recently captured near Port MacDonnell, South Australia weighing an impressive 102kg and measuring 191cm in length (175cm to the fork in her tail).

Southern Bluefin Tuna

Thanks to the tag retrieved by her captors, fisherman Matt Bell and skipper Dennis Heinicke, the CCSBT were able to collect a lot of data about how Bluey had spent the previous 20 years. For example, by examining her otoliths (deposits in the ear), they know her age and sex; by looking at her ovaries, they can review her reproductive history; by analysing the chemical composition of her muscles, they can understand her diet; and by downloading the historical data stored in her tags, they know that Bluey spent large parts of her life travelling:

“As a juvenile, [Bluey’s] migrations took her from the GAB to the Indian Ocean; upon maturing, she travelled between the Southern Ocean and the Indian Ocean, just south of Indonesia. It is here that adult SBT spawn each year.”

This diagram shows the distances covered and the patterns of juvenile SBT migrations:

Southern Bluefin Tuna Territory

It may seem like a waste of time, but this kind of cooperation between recreational anglers and scientists is providing important data on the changes that are affecting our seas and fish populations, including the effects of pollution and climate change. Well done Matt and Dennis, you’re an example to us all!

Southern Bluefin Tuna Growth

Image credit: Matt Bell and Dennis Heinicke.
Original article: News at CSIRO

James Green About James Green

James Green loves nothing more than casting a fly in pursuit of salmon, seatrout or, when the opportunity arises, a tailing bonefish, tarpon or permit.