Final answer:
Overharvesting, a result from the tragedy of the commons and enabled by advanced fishing technologies, is a primary threat to fisheries, leading to overexploitation and the collapse of ecosystems.
Step-by-step explanation:
Primary Threats Facing Fisheries
One of the most significant threats to global fisheries is overharvesting. As seen in the collapse of the once thriving western Atlantic cod fishery, modern fishing technologies such as factory trawlers have enabled massive catches, leading to unsustainable practices. The phenomenon is linked with the tragedy of the commons, where individual fishers lack the incentive to conserve resources in commonly shared fisheries, leading to overexploitation. Such unsustainable fishing practices are not only an economic issue but also an environmental and political one. Furthermore, the practice of fishing down the food chain has become prevalent, where fishers target smaller pelagic fish as larger predatory species decline. This threatens the balance of marine ecosystems and biodiversity, evidenced by the alarming reductions in populations of large marine vertebrates like sharks, tunas, and sea turtles. The loss of key species results in a restructuring of marine ecosystems, affecting food sources and other species in unpredictable ways. Ultimately, unsustainable fisheries practices may render aquatic systems nonviable as food sources, consequently impacting local economies and global food security.