You're thinking of the bluefins. They are the large apex predators, which is why they are also the highest in mercury -- they are accumulators. But a single bluefin fetches up to $10K and, today, are mostly bought by Japanese for sushi restaurants back home. The tuna you buy in cans at Safeway are smaller, more prevalent species (read: not as environmentally significant).
You're thinking of the bluefins. They are the large apex predators, which is why they are also the highest in mercury -- they are accumulators. But a single bluefin fetches up to $10K and, today, are mostly bought by Japanese for sushi restaurants back home. The tuna you buy in cans at Safeway are smaller, more prevalent species (read: not as environmentally significant).
Source: Tuna: A Love Story