Whether tuna is raw in sushi and sashimi, grilled as a steak, or scooped from a can, the fish is awash in controversy. Overfishing, mercury levels, and dolphins caught in nets meant for tuna account for this. Where once a tuna sandwich for lunch was a routine event, we no longer eat canned tuna without thinking about it. Still, almost everyone has a can in the cupboard, for that favorite sandwich spread with mayo, or without adornment to add substance to a green salad or a pasta sauce.
Most tuna absorb mercury by feeding on other fish or by eating plants exposed to it, whether naturally or through pollution. Albacore white tuna is a larger species, which generally has more mercury. Skipjack, a smaller species, is used in chunk light canned tuna. Mercury levels also depend on the age and provenance of the fish.