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Overfishing: A Non-Sustainable Use of the Oceans
The simplest way to define overfishing is "to catch so many fish that there are not enough remaining to replenish the population”(1). Overfishing occurs when we take too many marine resources at a rate faster than they can reproduce or recover. And as a result, fish populations are becoming severely depleted and some commercial species (e.g Southern Bluefin Tuna) are even at the edge of extinction (2,3). The end result of overfishing is a permanent collapse in fish supplies (10). Even when these events are isolated to specific regions, they have the potential to affect the global marine food web (12).
Until 2012, about 85% of global fish stocks have been "over-exploited, depleted, fully exploited, or in recovery from exploitation" (4). Large areas of seabed in the North Sea and Mediterranean, as well as the East China Sea of Asia, have become "desert[s] in the sea", where overfishing has wiped out almost all of the fish stocks (4,5). Fisheries in other parts of the world are also declining. West Africa, for example, has lost 50% of its coastal fisheries in the past 30 years (6).
Another example of overfishing is the Atlantic Cod stock between the 1970s and the 1990s. As technology increased in these years, cod stocks became more accessible to fishermen. Although these populations were once believed to be unlimited, the fish population soon plummeted to unsustainable levels. To ensure sustainable harvest of species, Total Allowable Catches (TACs) must be set to allow for recovery of fish stocks, in order to prevent similar situations to that of the Atlantic Cod. However, there are numerous economical and political implications for implementing TACs, especially in coastal communities that rely heavily on marine resources. As a result, these TACs are not often followed, or may not reflect scientifically accurate determinations.
Each country has control over their Exclusive Economic Zone (EEZ), an area of no more than 200 nautical miles off the coast of their continental territory, in which they have complete control over fish stocks and regulations (7). Areas outside of this zone, known as the high seas (7) are not regulated by any clear authority and suffer from a lack of effective fishery management (8). Therefore, "Tragedy of the Commons" arises, which was first introduced by Hardin as the idea that individuals exploit resources in their own self-interest, or, whoever gets to the resource first controls it. As each individual does this, the resource is eventually depleted and no one benefits.
The Tragedy of Commons
Here is a short video that explains the "Tragedy of the Commons".
Consequences of Overfishing
Overfishing can completely alter large ecosystems within different areas of the ocean, both coastal and offshore, by creating a snowball effect of disruption (Fisheries and Oceans Canada 2009). For example, overfishing a certain species can alter the balance of predator and prey interactions, which can destroy an ecosystem due to the interruption of important trophic cascades.
Overfishing can threaten cities and smaller towns that live along the coast and depend on the seafood industry for employment and food. Depleting the fish stock in these areas threatens food security and livelihoods within the area (World Wildlife Fund 2019).
Oil and waste pollute byproducts of the fishing industry continue to accumulate as overfishing becomes more prevalent. Fishing boats release toxic chemicals and oils into the water, as well as pollute the water with trash. This is increasing the pollution in the ocean, both solid and liquid waste, that poses significant threats to wildlife (Bhatnagar 2018).
Damaging fishing practices can alter marine habitats, particularly when using bottom trawling nets. These nets are dragged along the ocean floor, disrupting the environment of any number of species. Additionally, trawling is a large source of bycatch, in which undesirable species are caught in a net and subsequently discarded. This has led to unintentional population decline in a number of species, most notably sea turtles.
In order to prevent overfishing, fishermen need to be incentivized to stop catching specific amounts of fish at certain locations. It is all dependent on Maximum Sustainable Yield (MSY), which is the maximum amount of a species that can be harvested while maintaining the ability to recover the population (11). By limiting, banning, or regulating the use of bottom trawling nets, juveniles can be protected, allowing them to reach sexual maturity and reproduce before they are caught. Additional measures on trawling nets can reduce the bycatch of unwanted species. For example, Turtle Excluder Devices (TEDs) are a popular way of ensuring that sea turtles are not accidentally caught in fishing nets. Setting an Individual Fishing Quota would incentivize fishermen to catch the largest and most mature fish and avoid bycatch or juveniles (11). This would be beneficial to both the fish and the fishermen because it prevents exploitation of stocks and the economic collapse of species-specific fisheries that follows the crash of a population.