Video: 快猫短视频s catch Atlantic bluefin tuna, extract stony growths called otoliths from their ears and determine where they were born (Footage courtesy: Jay Rooker, Texas A&M University)
Bluefin tuna born on opposite sides of the Atlantic spend their juvenile years together, before returning to natal waters in the Gulf of Mexico and the Mediterranean Sea to breed.
The findings could have implications for the management of what were once thought to be entirely distinct populations.
The study, led by researchers at Texas A&M University and the University of Maryland, looked at chemical signatures in the fish鈥檚 inner ear to determine where each of the highly endangered fish came from.
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Specifically, the team looked at a bone-like structure called the otolith, a calcium-carbonate deposit that is laid down after a fish hatches. These carry different concentrations of oxygen isotopes depending on whether the fish developed in cool Mediterranean waters 鈥� eastern bluefin 鈥� or warmer Gulf waters, which spawn western bluefin.
鈥淚t鈥檚 a birth certificate that we can retrieve during any phase of the fish鈥檚 life and determine where they spent their first year,鈥� says , one of the lead authors of the paper.
New perspective
The findings showed that nearly 60% of more than 150 juveniles found in waters off the mid-Atlantic region of the US came from the Mediterranean, with the remainder coming from the Gulf of Mexico. The study also found that the fish return to their side of the Atlantic by the time they are adult tuna.
鈥淚f you are a fisherman from Maryland going out and seeing lots of juvenile bluefin tuna, you might think the population is fine,鈥� Secor says. 鈥淏ut when you realise they are being subsidised from the Mediterranean, it gives you a different perspective.鈥�
It is the first single study to show that the populations mix as juveniles but then return to their natal waters to spawn, and allows for finely tuned fishery management, says of the University of British Columbia. 鈥淏ut the fact that the science has gotten stronger still doesn鈥檛 change that fact that it isn鈥檛 being used by managers.鈥�
The , which manages the two populations, still treats them as distinct, non-mixing groups.
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