Thursday, May 14, 2015

The Great Yellowfin Adventure

A yellowfin tuna finning at the surface, swimming right.
The second dorsal fin sweeping back and the top of
the caudal (tail) fin visible.
Yesterday, in the early hours of the evening following class on the quarterdeck, I spotted a flock of birds wheeling in the distance. They were close enough that, with Captain Pamela’s permission and patience, we changed course to take a look. Birds are the sentinels of the sea – if there is food, they find it. I was sure it was  some pelagic predators pushing their prey to the surface that attracted those birds, and we were not disappointed.

We made one pass through the school of Yellowfin tuna, exclaiming as we saw them finning at the surface. The view from aloft was incredible – Hannah and Andreas acted as spotters, watching for the most tuna activity and guiding the ship. As the sun sank lower in the horizon, we motored through the school three more times, watching these breathtaking creatures do what they do best – hunt.
But we were also on the hunt. While I think I would have been happy with this gorgeous view regardless of a catch, there was also science to be done, and a salivating crew. I study tuna biomechanics – what gives these fish their swimming power, efficiency, agility, grace? Specifically on this cruise, I’m interested in the tail joint, tendons, and driving muscle groups. And so, for the time being, the SSV Robert C. Seamans turned fishing vessel.

On our fifth pass through the school, professor Barb Block called out, “Alright, one last try here.” A moment later, just as the sun touched down on the horizon, a shout went up from the quarterdeck – we had a hit! Nick seized the fishing rod, and a record struggle began, rod arching and spool singing. Night falling, Ryan switched in, followed by Robbie as we launched the small boat with Jan, Ethan, and Ryan. Several hours and sweat-soaked shirt later, Robbie stepped down to Nick. Ryan came back aboard and Robbie joined the small boat, and relieved Nick. Don took a turn. Nick picked it up once more. What a fish, to fight us for five hours, well into the darkness, and through seven shifts of fishermen!

The prize catch- the largest yellowfin ever
 landed on the RCS
At long last, we landed the tuna in the small boat, prompting a roar of cheers from the restless crowd. The fish was brought in by roped tail to the science deck-and what a beauty!  155 cm curved fork length, which puts him (a male) at around  130 to 140 pounds and about 4 years old. We laid him out and started the science and sashimi process. Our resident tuna expert and all-around pelagic predator expert Dr. Barbara Block dug in. We took samples for genomics, mercury, and stable isotopes, and also collected the fins for hydrodynamic analysis in a water tunnel upon our return to land. Amazingly there were two skipjack tunas in the Yellowfin’ s tummy.  Finally, we filleted the fine fish, saving half of the tail for my biomechanics work the next day, but plenty to fill the bellies of all aboard for many days to come.

Peace, love, and fish tales/tails,


Marina Dimitrov

UPDATE: post-dissection leftovers GLOW! WHAT? – will be investigating. This fish just keeps surprising us!


Mark van bergen said...

Sounds like you are having a better time then ever was expected. Congratulations on the perfect tuna for you to study, that is absolutely amazing. Good luck on the dissection, I'm cheering for you guys. Happy fishing and smooth sailing. My best wishes to Marina and everyone on the Bobby C.

Alexander said...

NICE FISH! Tight Lines