Levels of large predatory fish in the global oceans were estimated to be about 10% of their pre-industrial levels by 2003. Large predatory fish are most at risk of extinction; there was a disproportionate level of large predatory fish extinctions during the Cretaceous-Paleogene extinction event 66 million years ago. Creation of marine reserves has been found to restore populations of large predatory fish such as the Serranidae — groupers and sea bass.
Predatory fish switch between types of prey in response to variations in their abundance. Such changes in preference are disproportionate and are selected for as evolutionarily efficient. Predatory fish may become a pest if they are introduced into an ecosystem in which they become a new top predator. An example, which has caused much trouble in Maryland and Florida, is the snakehead fish.
Predatory fish such as sharks and tuna form a part of the human diet, but they tend to concentrate significant quantities of mercury in their bodies if they are high in the food chain, especially as apex predators, due to biomagnification.
Predators are an important factor to consider in managing fisheries, and methods for doing so are available and used in some places.