The tuna that I’m referring to here isn’t the tuna that you’ll find on the shelves at your local supermarket (i.e. Albacore in the US), but Southern Bluefin Tuna (SBT) - a larger, rarer species that currently is harvested mainly for the higher end sushi markets (or at least that is my current understanding). Wild ocean populations have seen drastic declines from overfishing in the past, and currently there are strict international quotas on how much can be harvested. For this reason, and also for issues of quality and availability, a good number of SBT is now “ranched” in Australia - meaning a set number of fish are wild caught, towed back close to shore, and then grown in net-pens to be harvested following a variable period of around two to eight months. The entire process is outlined nicely in a National Geographic Channel episode called Tuna Cowboys (I tried to find a free link to the video online, but didn’t have any luck). Check it out if you get a chance.
Anyway, on this occasion I showed up to the dock at around 4:30am for the two hour boat ride out to the pens. When we got there, it was just getting light enough to see without the floodlights.
The divers immediately jumped in the water and, aided by the crew, began setting up a purse-seine net within the larger net-pen to corral the tuna into a smaller area.
Once corraled, the divers estimate the number of fish and then get to work catching them…by hand!
These fish are about 100lbs each at the time of harvest, can swim at speeds over 40mph, and there’s well over a thousand in each net. I haven’t experienced it myself, but I would imagine that catching them in this manner would be a daunting task, but the divers appear to manage it alright, and pretty quick too.
When a diver catches a fish, he brings them up to the boat where they are pulled up on board, processed, and immediately transfered to super-chilled water for transport in the hold over to the Japanese freezer boat moored not far from the pens (in this instance) or for fresh transport directly to the market.
They make the trasfer using multiple cranes and then the fish are further processed before making their way to Japan
It’s been quite interesting to work with this species, as coming from Idaho and NY, my former knowledge about saltwater fish in general, much less tuna, was fairly limited. Additionally, tuna is also relatively unique in that they are warm blooded. Not quite the same physiologically speaking as warm blooded mammals, but they are able to keep internal body temperatures of around 80°F in water around 40°F which makes for investigations into physiological mechanisms different from other species.
That’s about all I have to say about tuna for the moment. I think in a week or two I’ll put something together about the climbing and traveling in Tasmania - some beautiful places and a lot of rock. Later-
Very interesting.
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