Because of the patchy availability of food in the open ocean, predatory species like this yellowfin tuna have to travel vast distances to survive. Its torpedo-shaped body is designed for speed, allowing the mighty fish to chase down fast-moving prey.

Adult yellowfin, which are also known as ahi tuna, have few predators of their own, except for humans. The yellowfin is tremendously important to commercial fisheries, and the total world catch amounts to at least 800,000 tons per year. But because the fish reproduce rapidly (a spawning female produces several hundred thousand eggs, Pepperell writes), researchers believe the yellowfin is not in danger of being overfished. That's a stark contrast to the situation facing its endangered relative, the bluefin tuna.