What is overfishing?

Cod caught in a fishing net in the Gulf of Maine

Overfishing is defined as the "the practice of commercial and non-commercial fishing which depletes a fishery by catching so many adult fish that not enough remain to breed and replenish the population. Overfishing exceeds the carrying capacity of a fishery."

Simply put, overfishing occurs when fish or marine species are fished at a rate faster than which they can reproduce. Numerous scientists claim that overfishing is the biggest threat to the oceanic environment, surpassing that of other detrimental human effects such as pollution. Increases in the demand for fish as a source of food, as well as advancement in fishing devices have allowed larger amounts of fish to be caught in shorter periods of time. The ability to obtain a higher amount of marine organisms per catch does initially feed more people globally while providing a greater revenue, however the harmful effects are proving to be substantially disastrous over time. Increased fishing could potentially result in smaller catches due to marine stocks being depleted past their natural replacement rate (i.e., populations subjected to overfishing are removed past their maximum sustainable yield (MSY), an estimate of the largest amount of species that can be removed without having an effect on their replacement rate). This is causing many marine species and ecosystems to be lost. Not only is the natural ecological balance of our oceans being ruined, but humans are at risk of losing fish as a valuable food source.


Types of overfishing

• Growth overfishing: arises when fishing rates bring the total biomass of marine stock lower than the number of biomass gained due to natural growth. Also occurs when too many fish become fished before the stock reaches the size optimum for maximum growth and productivity.
• Recruitment overfishing: occurs when spawning biomass of given population is reduced, which ultimately does not allow for enough larvae and recruits to be produced and replenish the population.
• Ecosystem overfishing: occurs when members of a stock are fished at a rate that changes the composition of the ecosystem drastically, often leading to system-wide negative effects.
• Economic overfishing: results from inefficient use of fishery resources. The economic overfishing limit is usually identified as the point at which the fishing effort is greater than the total profit of the fishery. In other words, the total number of fish caught is not enough to cover the costs of fishing.
• Malthusian overfishing: a term used to describe when fishing levels are too high for a fishery to be sustainable. After continuous exploitation leads to lower catch levels, fishers may incorporate more destructive fishing practices to yield larger catches.

Destructive fishing methods

Trawl fishing in action

Commercial fishermen are paid to catch fish in order to appease demands from local markets and restaurants. Unsurprisingly, there are many more effective methods being utilized other than the classic hook & line. A great deal of these fishing methods, however, are exploitive and cause unsustainable and long term damage to ecosystem health:

• Bottom trawling: an extremely harmful but common fishing method that involves the use of large nets by dragging them across the ocean floor in order to obtain huge amounts of fish quickly. These nets are not species-specific, and often end up catching numerous species that are never used. The nets are fixed with large metal plates and rubber wheels; they crush almost everything they come into contact with as they move along the deep sea floor. Evidence shows that life in the deep waters are very slow to recover from such effects, ranging from decades to centuries. In some cases, they never recover at all.

Dynamite fishing in Southeast Asia

• Dynamite fishing: also known as 'blast fishing', is performed with dynamite or homemade bombs. The resulting explosion kills a high number of fish, as well as many other marine organisms within the vicinity of the blast. Dead fish float to the top or sink to the bottom, and are collected relatively easily by fishermen. This technique is obviously detrimental to ecosystems, and are especially devastating to coral reefs. Fortunately, this practice is now illegal in many parts of the world. 
• Cyanide fishing: an illegal fishing method practiced in various Southeast Asian Countries, fisherman use cyanide to capture fish inhabiting coral reefs. The fish often die immediately, during shipping, or after a few days due to digestive damage.
• Muroami: a fishing technique used on coral reefs in Southeast Asia, it incorporates a large, circular net equipped with large stones secured by ropes. The stones are used to repeatedly pound and literally crush the coral reefs into small pieces, in order to scare fish out of their homes and be captured. This is an overwhelmingly disastrous method and often leaves coral reefs incapable of recovery.

It is clear that these fishing techniques are contributing to the global problem of overfishing. Too many people are far too content with the short term gains provided by these fishing methods, that they fail too see just how harmful the long term effects are. Another growing problem is that technology is continually advancing in the fishing industry. Fishermen can now fish in factory boats, which do not require them to report back to port regularly, and can therefore stay out at sea for months.


References

1. Destructive Fishing Practices. 2012. Food & Agriculture Organization of the United Nations. 3 March 2012 <http://www.fao.org/fishery/topic/12353/en>. 
2. Overfishing: A Global Disaster. Pepijn Koster. 2007-2011. 3 March 2012 <http://overfishing.org>. 
3. Rubec, Peter. "The need  for conservation and management of Philippine coral reefs." Environmental Biology of Fishes 23.1-2  (1988): 141-154. Online.