Among the most recognized deep-sea species at-risk are orange roughy and Patagonian toothfish, better known as Chilean sea bass. In the deep ocean off the Pacific Northwest, sablefish – also known as black cod – are another depleted species. Deep-sea fishes grow slowly because of limited food sources and slower metabolisms and many don't reach sexual maturity for 30 to 40 years, Heppell said. The harvest of older fish may have an even greater impact on these threatened populations because older fish are more likely to breed successfully than younger fish.

"When you buy orange roughy at the store, you are probably purchasing a filet from a fish that is at least 50 years old," Heppell said. "Most people don't think of the implications of that. Perhaps we need a guideline that says we shouldn't eat fish that are as old as our grandmothers."