Sunday, May 19, 2013

And Then There Were More...

We've found a few bluefin tuna larvae in the last few days, including one station with four! That may not seem like a lot, but in reality finding any bluefin is a big event because we have been finding none at most other spots. We think these larvae were probably born in the Bahamas, not transported from elsewhere, because they're only 5 mm long or less -- that means that they're just a few days old, and couldn't have come from far-off lands like the Gulf of Mexico or the Mediterranean Sea. This means that at least a few tuna adult spawned in the region (North of the Bahamas). Were these adults lost, testing out a new spawning area, or just being rebels? More work is needed! Stay "tuna-ed" to see if we find more bluefin over the next week and a half (FYI, in the Gulf of Mexico, we find hundreds of bluefin tuna larvae in our samples). 

P.S. You might be wondering how we identify tuna larvae as a bluefin tuna vs other species of tuna. It gets to be a difficult task sometimes, as the only differences between the skipjack, blackfin, yellowfin, and bluefin tunas are tiny pigments, some of which are barely noticeable spots. At other times DNA is the only way to correctly identify a tuna to the species level -- a lot of specimens lose their heads, tails, or other crucial portions of their bodies after getting beat up by the currents, our nets, by other organisms, or through handling. Compare the two below and see if you can tell them apart -- it takes a trained eye, some patience, and a powerful microscope to identify to the species level. These larvae were photographed in seawater to preserve color and pigments!

Larval skipjack tuna ID
Skipjack Tuna (Katsuwonus pelamis)
This guy has black pigments both before and after his brain (two black arrows) ... he also has one black spot on the lower part of his tail but never has any pigment on the top of his body or on his chin.
Larval bluefin tuna ID photo
Bluefin Tuna (Thunnus thynnus)
Compared to the skipjack above, the bluefin doesn't have pigment in front of his brain or on his chin. He does have spots on both the top and bottom of his body. 

All photos are the property of NOAA. Reproduction, manipulation, or downloading are prohibited without permission by Kat Dale. Thanks!

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