Science, Tech, Math › Animals & Nature How Overfishing Affects Fish Populations Overfishing can cause depletion of extinctions of fish populations Share Flipboard Email Print wildestanimal / Getty Images Animals & Nature Marine Life Key Terms Marine Life Profiles Marine Habitat Profiles Sharks Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Forestry Dinosaurs Evolution View More By Jennifer Kennedy Marine Science Expert M.S., Resource Administration and Management, University of New Hampshire B.S., Natural Resources, Cornell University Jennifer Kennedy, M.S., is an environmental educator specializing in marine life. She serves as the executive director of the Blue Ocean Society for Marine Conservation. our editorial process Jennifer Kennedy Updated March 15, 2019 Simply put, overfishing is when so many fish are caught that the population can't reproduce enough to replace them. Overfishing can lead to depletion of or extinction of fish populations. The depletion of top predators, like tuna, enable smaller marine species to overpopulate affecting the rest of the food chain. Deep sea fish are thought to be more at risk than shallow water fish due to their slow metabolism and smaller rates of reproduction. Types of Overfishing There are three types of overfishing: Ecosystem overfishing happens when a predatory species, like tuna, has a sharp decline in population enabling smaller marine species to overpopulate.Recruitment overfishing occurs when a fish is harvested before it is old enough to reproduce.Growth overfishing is when a fish is harvested before it has reached its full size. Overfishing in the Past Some of the earliest examples of overfishing occurred in the 1800s when the whale population was decimated in order to produce high-demand products. Whale blubber was used to create candles, lamp oil and the whalebone was used in everyday items. In the mid-1900s there was a sardine population collapse on the West Coast due to climate factors combined with overfishing. Fortunately, sardine stocks had rebounded by the 1990s. Preventing Overfishing As fisheries have returned smaller yields each year governments around the world are looking into what can be done to prevent overfishing. Some of the methods include expanding the use of aquaculture, more effective enforcement of laws governing catches, and improved fisheries management. In the U.S., Congress passed The Sustainable Fisheries Act of 1996 which defines overfishing as "a rate or level of fishing mortality that jeopardizes a fishery's capacity to produce maximum sustainable yield (MSY) on a continuing basis."