In contrast to the large number of terrestrial extinctions that have taken place over the past 12,000 years, there have apparently been very few marine extinctions. But these small losses should not be reason for complacency. During the past 50 years, government supported, commercial fishing has resulted in the collapse of about a thousand populations that once supplied most of the world’s seafood. For the collapsed species, now existing as small remnants of their former population sizes, the future is bleak. They suffer from loss of genetic diversity, inbreeding depression, and depensation. Because marine species were eliminated by historic climatic changes, continued global warming is likely to result in the extinction of small populations that already have a precarious existence. They may be considered evidence of an extinction debt that must be paid as the climate change becomes more severe. For some of the remnant species, extinction can be avoided if there is a rapid management conversion to the use of more marine protected areas (MPAs) and extensive ocean zoning where fishing is prohibited.