Bluefin tuna are widely distributed throughout the northern hemisphere, in both the Atlantic and Pacific oceans. In the western Atlantic, they range from Newfoundland and Labrador to Brazil and in the eastern Atlantic, their range stretches from Norway to the Canary Islands off the coast of Africa. Bluefins are also found in the Mediterranean and Black Sea. They undertake extensive migrations, appearing on Canada's Atlantic coast from June to early autumn.

Bluefin tuna are hefty fish with a large head and a body that tapers sharply near their tail fin. Their first dorsal fin is long, flat and shaped like a sail, and the second is thin and curved. Their tail fin is very slender and strongly indented. Bluefins are dark blue on their dorsal side, becoming silvery-white on their flanks and belly. They can grow to more than three metres in length and weigh over 650 kilograms. They are estimated to live about 20 years.