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Determining The Age And Birth Ground Of A Tuna Canada, September 20, 12

Alberton tuna fisherman, Doug Fraser, who sits on the International Commission for the Conservation of Atlantic Tuna, said information obtained from a DFO study could prove helpful during quota allocation discussions.


Research, based on stable isotope ratios, determines where the fish was born

From a heap of tuna heads on the floor at Royal Star Foods in Tignish, Dheeraj Busawon selects one, takes measurements and then slices down the middle with a cordless power saw.

Setting the saw down and picking up a pair of tweezers, he plucks out two small bones, called otoliths. There are three sets of otoliths, or ear bones, in tuna, but Busawon, a Department of Fisheries and Oceans scientist, is only looking for the largest pair.

To a tuna, otoliths are important for hearing and balance. They serve two different purposes for scientists and resource management personnel, telling the age and the natal origin of the fish.

“I take one otolith and put it in a resin,” Busawon explains. “I take a cross-section of it and view that under a microscope and it is like counting rings on a tree, and it gives you the age.”

Determining the natal origin — where the fish was born — is a little more time consuming. Using a tiny instrument similar to a dental drill, the center of the otolith is made into powder and sent to a laboratory in the United States for chemical analysis.

Research, based on stable isotope ratios, Busawon explained, determines where the fish was born.

Each fish head is numbered, allowing researchers to match up their information with the weight of the fish and where it was caught.

Alberton tuna fisherman, Doug Fraser, who sits on the International Commission for the Conservation of Atlantic Tuna (ICCAT), said the information could prove helpful during quota allocation discussions.

He said fishermen willingly parted with their fish heads for the scientific project.

“Hopefully this project will help science take something to the next step and prove that our stock is healthy,” Fraser commented.

“It’s important, because there’s so much focus put on the fishery as being over-fished,” Fraser said. “People’s got to understand Canada is leading the way here in being responsible,” he added.

Research using the small ear bones has been going on for decades, Busawon indicated.

Earlier this summer he examined about 30 tuna heads Royal Star had in storage since last year. Now he is doing his research on recently caught fish, including a couple of dozen landed in Alberton and Tignish in the last week or so. Most of those fish were caught on the teeming MacLeod’s Ledge, but where they came from is a discussion Fraser is confident will soon be settled. He acknowledges, though, the study will likely find some mixing between fish born in the Gulf of Mexico and fish originating from the Mediterranean. It might even help identify another spawning area, he suggested.

There have been arguments in the past, Fraser said, that most of tuna being caught in the Gulf of St. Lawrence more than 20 years. He said there have been younger age class fish showing up in recent years and tuna have been abundant all around P.E.I. for the past five to six years.