Researchers recently reported in the journal Science that 60 percent of the juvenile bluefin tuna found off the East Coast of the United States had been born in the Mediterranean. The other 40 percent were born in the Gulf of Mexico. When the fish reach sexual maturity, however, at about 5 years old, they go home to spawn in their birthplace.

The Atlantic bluefin fishery management has been based on the assumption that the Atlantic and Mediterranean populations were separate.

I wasn't clear on the implications of this study and when I tried to learn more about bluefin tunas. I opened a can of worms. With big money involved, multiple countries concerned, tradition to stand on and countless biological unknowns, the answers to questions about bluefins depend on whom you ask.

Researchers, government agencies, environmental groups and fishing organizations have disparate opinions.

It's easy to see why these largest and fastest of all tunas are hard to study. A bluefin can swim 45 mph and cross the Atlantic in 60 days. Some bluefins swim across the Pacific Ocean and back, and others circle the Southern Ocean.

These three areas host one species of bluefin each. The largest, Thunnus thynnus, swims in North Atlantic and Mediterranean waters. The ones in North American waters are often called Western Atlantic, Northern or giant bluefins. The ones on the European side are known as Mediterranean bluefins. These are all the same species, however, and researchers now know the young of the two populations are mixed.

The Atlantic species is the largest of the bluefins, growing to 1,500 pounds and measuring 14 feet long. They live 15 to 30 years.

The second largest, Thunnus orientalis, is called the North Pacific bluefin. These tunas spawn in the Sea of Japan, swim up to 6,000 miles across the Pacific to North America and return to their birthplace to reproduce.

The Pacific bluefin weighs up to 1,200 pounds, grows to 10 feet long and lives up to 25 years.

The third bluefin species, Thunnus maccoyii, is the Southern bluefin. This tuna swims around the Southern Ocean, mainly between 30 to 50 degrees south. The only known breeding place for this species is around Java, Indonesia, in the Indian Ocean.

The Southern bluefin is the smallest of the three, but it's no tiny tuna. It weighs 800 pounds, measures 8 feet long and lives 20 to 40 years.

The lucrative sushi market has driven anglers to hunt bluefin tunas so hard that all three species are now critically endangered. But even though the fishery isn't sustainable, it's hard to stop fishers from taking bluefins when they bring in so much money. In Japan one large bluefin sold for $173,600.

The irony is these fish can be hazardous to eat. The long-lived bluefins accumulate dangerously high levels of mercury in their flesh.

After days of reading, I understand more about bluefin tunas and now have my own opinion of the situation: Through a combination of advanced fishing technology, poor international cooperation, consumer indifference and plain old greed, we've driven to near extinction one of the world's most magnificent marine animals.

We can help these fabulous fish - and our own health - by not eating them.