Southern Bluefin Tuna (Thunnus maccoyii)

Largely due to overfishing, the Southern Bluefin Tuna is listed as "critically endangered." If its population continues to decline, the species faces the possibility of extinction. It's not alone. Scientists classified the Atlantic Bluefin Tuna as "endangered" and Bigeye Tuna as "vulnerable." See more endangered species on our Endangered Vertebrates Slideshow.