Over exploitation

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Overexploitation or overfishing is the removal of marine living resources to levels that can not sustain viable populations. Ultimately, overexploitation can lead to resouce depleation and put a number of threatened and endangered species at risk for extinction.

Fig. 1. Overexploitation of fish stocks is a major threat to marine biodiversity in Europe. Photo © OAR NURP,NOAA

The problem

The exponential growth in human population experienced in last decades has lead to an overexploitation of marine living resources, as a consequence of an increasing demand for food. Worldwide, fishing fleets are two to three times as large as needed to take present day catches of fish and other marine species and as what our oceans can sustainably support. The use of modern techniques to facilitate harvesting, transport and storage has accelerated this trend. According to the United Nations Food and Agriculture Organization (FAO) over 25% of all the world's fish stocks are either overexploited or depleted and 52% are fully exploited [1]. Thus a total of almost 80% of the world's fisheries are fully to overexploited, depleted, or in a state of collapse. Although, these estimates are considered rather conservative. Recently, a study showed that 29% of fish and seafood species have collapsed (i.e their catch has declined by 90%) and are projected to collapse within by 2048 [2]. Worldwide about 90% of the stocks of large predatory fish stocks are already gone.

Overexploitation effects

All fishing activities, if not conducted in a sustainable non-destructive manner, can lead to overexploitation of marine living resources. Overexploitation of marine resources has major impacts on marine systems as a whole, but target species are generally the most impacted.

Fishing effect can be divided into: direct effect and indirect effects. Direct effects are related to target species and by-catch species. When recruitment of target species is relatively high, the average size of individuals is affected because larger individuals tend to be harvested and populations display signs of growth overfishing. When adult populations are heavily exploited the number and size of the adult population (spawning biomass) is reduced to a point that it has not the reproductive capacity to replenish itself, leading to recruitment overfishing. Direct effects of fishing also include physical disturbance by fishing gear than can cause scraping, scouring and resuspension of the substratum. The effects vary according to the gears used and the habitats fished [3]. Indirect effects of overexploitation and fishing in general include effect of "goast fishing", trophic cascading effects [4] and food web-competion. For more information of the direct and indirect effect of fishing refer to the article Effects of fisheries on European marine biodiversity.

References

  1. The State of World Fisheries and Aquaculture (SOFIA) www.fao.org/sof/sofia/index_en.htm
  2. Worm, B. et al. Impacts of biodiversity loss on ocean ecosystem services.Science 314, 787-790
  3. >Jennings, S.& Kaiser, M. (1998). The effects of fishing on marine ecosystems. Adv. Mar. Biol. 34: 201-352.
  4. Pauly, D.; Christenen, V.; Dalsgaard, J.; Froese, R.; Torres, F. Jr. (1998). Fishing Down Marine Food Webs. Science 279: 860-863


The main author of this article is Atalah, Javier
Please note that others may also have edited the contents of this article.

Citation: Atalah, Javier (2009): Over exploitation. Available from http://www.coastalwiki.org/wiki/Over_exploitation [accessed on 15-08-2020]