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Many ecologists believe that the largest threat to marine ecosystems is now overfishing. The world’s appetite for seafood is pushing the oceans’ limits, leading to devastating consequences for marine ecosystems. Overfishing profoundly changes oceans, and these changes may not be reversible.Populations of predatory fish are dwindling at alarming rates due to overfishing, indicating unhealthy ecosystems. Since industrial-scale fishing was introduced in the 1950s, the vast majority of fish used for food, such as tuna, marlin, swordfish, halibut and cod, have been depleted. The reduction in these predator species has caused ecosystem shifts in which commercially important fish are replaced by small fish that feed on plankton.

These changes put the very functioning and structure of marine ecosystems at risk, threatening the lives of people dependent on the oceans for survival.The mismanagement and over-exploitation of fisheries has led to collapses, such as the disaster that occurred in Newfoundland, Canada in 1992. The collapsed cod fishery affected approximately 40,000 jobs. Fisheries in the Baltic Sea and the North Sea are dangerously close to collapsing as well.

Climate change exacerbates the stress already experienced by marine stocks. Rising global temperatures cause rising sea surface temperatures and levels; decreases in ice covers; and changes in wave conditions, circulation patterns, and salinity. These changes have a significant impact on the productivity of marine ecosystems and fisheries.

Although the specific effects that global warming will have on marine ecosystems and fisheries depends on many variables, the Intergovernmental Panel on Climate Change has forecasted dire consequences. If climate change and overfishing continue, new populations of fish will be less abundant and small, opportunistic species will flourish over larger, more commercially valuable species. Small-scale and subsistence fishers will suffer the most from these changes.

Climate change may also result in a more serious risk of oxygen depletion in our oceans; changes in precipitation, lake levels and freshwater flows; introduction of new species and disease organisms; and competing demand for coastal areas.

In order to combat these changes, the fishing industry must encourage collaboration at both the regional and global levels to promote best practices, prepare contingency plans for fisheries that will suffer the most from the changes, analyze the sustainability of aquaculture, encourage interdisciplinary research on the subject, and formally address the issue of global warming through industry management administrations.