Saltwater fish

Overfishing is defined as the mass removal of fish from a body of water that results in halting the ability for breeding populations to replenish what has been removed. Fish is one of the most popular foods in the world and consumption has continued to rise with the growing human population and will continue to do so. The value of the global seafood market has seen a 15% increase from 2016 to 2020 and is projected to increase even more by 2023.[7] Although it provides many people with a source of food, the global seafood market is a major threat to the biodiversity of fishes. Bycatch is a direct effect of overfishing and is defined as the unwanted capture of different marine organisms during industrial fishing. This results in many different species of fish dying after they are captured and discarded. Data on bycatch is often unclear and not well recorded but it is estimated that the U.S. alone discards 17-22% of their catch annually.[8] The Mesopredator release hypothesis is one of the indirect effects of overfishing that is also often referred to as "fishing down the food web". This phenomenon means as fisheries deplete large apex predatory species, mid-sized predatory species increase in abundance and assume the role as top predators on the food web.[9] This impacts the food web in marine environments and disrupts the balance of the ecosystem and is likely to cause trophic cascades.

Profitable fish stocks like the bluefin tuna are decreasing in numbers because of high demand. According to the IUCN Red List, the Pacific bluefin tuna, Atlantic bluefin tuna, and southern bluefin tuna are classified as vulnerable, endangered and critically endangered[10] all due to over-exploitation.

According to the IUCN Red List, the oceanic whitetip shark is considered critically endangered because of its value in the seafood market. Their rapidly declining population is due to people overfishing them for their fins. They are a popular species of shark used in shark fin soup because of the size of their fins. All sharks are used for shark fin soup, however, certain species of sharks are preferred over others because of the large size of their fins.

The great white shark is listed as vulnerable on the IUCN Red List because its fins are commonly used in shark fin soup and has led to people over harvesting them for their fins. This shark belongs to the class Chondrichthyes that includes all sharks, skates and rays. The great white shark is one of the many examples of shark species threatened by human consumption because of the shark fin soup, large population declines of this class has been noted since the early 2000s due to the high demand for their fins, gill rakers and liver oil.[11]

The Atlantic cod was historically abundant in the waters off the coast of New England. Due to its low fat content and dense white flesh, this fish is a popular choice among humans. Now considered vulnerable,[12] its populations have both decreased in abundance and their distribution has shifted from northern to southern areas due to overfishing.[13]

Photo of cage aquaculture located in Australia

Aquaculture is defined as the farming of aquatic organisms in controlled environments for the purpose of providing food and resources for humans. Aquaculture can take place in both marine and freshwater environments, however, because this is the saltwater fish page this entry will only cover the effects of aquaculture on marine fishes. The rising global demand for fish has contributed to the increase in aquaculture. Due to the decline of many wild fish stocks, aquaculture is the fastest growing food production system that contributes about 50% of the worlds fish supply.[14] There is a lot of debate on whether or not aquaculture is an environmentally sustainable practice, yet the socioeconomic benefits that humans receive is tough to argue against. That being said there are significant negative effects that aquaculture, especially cage aquaculture, has on the surrounding environment.

Cage aquaculture involves rearing aquatic organisms in natural water sources while enclosed in a mesh/net cage that allows water from the surrounding environment to freely flow in and out. Cage aquaculture in marine environments has been particularly controversial because of the effects it has on the surrounding ecosystem thus, affecting wild marine fish populations. The main impacts of cage aquaculture are reduced water quality from fish sewage, high potential of genetic pollution of wild stocks due to escapees from aquaculture cages[15] and the possibility of introducing an invasive species if the fish being reared are non-native . Fish sewage is the combination of fish feed, fecal material and antibiotics that is accumulated on the seafloor and in the water column from fish that are being farmed. It is not only harmful to wild fish stocks but it also poses a threat to marine plant life which is often a food source for wild fish stocks. Fish sewage is harmful because it pollutes the surrounding ecosystem and can cause problems like eutrophication, transmission of parasites and diseases to wild populations[16] and developmental abnormalities on surrounding wild fish.[17] Genetic pollution of wild fish populations is a common risk that cage aquaculture faces. For example, there are many scientific papers that have examined the effects of Atlantic Salmon escaping from their enclosures and interacting with wild populations. Farmed salmon have lower fitness (low survival rates and reproductive success) than a wild salmon would due to differences in artificial and natural selection.[18] Artificial selection that chooses phenotypic traits that are desired for human consumption will alter the genetics of wild stocks if farmed fish interact and breed with wild populations. This would result in the reduction of fitness related traits that wild stocks possess which is a serious threat to these populations.