Overfishing

Overfishing

The use of exploitive and destructive fishing practices on coral reefs is a globally extensive problem with a long history. Indeed, ecological species extinction precedes that by all other factors, including pollution, water quality degradation, and climate change. Despite its reputation as an early, destructive anthropogenic influence on coral reefs, overfishing is also a currently growing problem. The global fishing effort has steadily increased since 1970 with no signs of abatement in the near future.

History

A variety of evidence exists for determining historical fishing pressure on coral reefs. This evidence includes paleological sedimentary records, archeological records from human coastal settlements, written historical documents, and ecological records from scientific literature. Using these sources, three periods of fisheries exploitation have been identified: aboriginal or subsistence exploitation, characterized by simple technologies and a limited geographic extent, colonial or systematic exploitation, characterized by merchantile powers utilizing distant resources, and more recently, geographically pervasive global exploitation. This article focuses on the latter period.

Causes

The exploitation of coral reef fisheries is largely due to increased demand on the global market for reef fish (Cinner and McClanahan, 2006). The issue of overfishing is therefore difficult to mitigate, because it is tied to global economic and population growth and increasing demand on a global scale. Since it is driven by global economic growth, it would require at least 20-50 years to change the trend of overfishing, even if strong effort to stop the issue began immediately. Even as fish populations are being depleted and global catch declines, fishing pressure continues to increase (Bradbury, 2012).

(Technology)

Effects

Overfishing of reef environments has significant impacts on ecosystem function. The removal of top predators leads to explosions in the populations of lower level consumers. These consumers then overgraze on coralline algae and cause coral abundance to decrease ((Stephens, 2012). Eventually, as more slow growing corals are removed, fast-growing seaweeds can overtake the environment, replacing coral (Smith 2010). However, a stable population of herbivorous fish is necessary for healthy ecosystem function. Sufficiently dense populations of grazing fish and sea urchins abate harmful algae growth (Smith 2010). Overfishing of herbivorous fish can also have profound ecosystem effects... Heavy fishing and harmful fishing techniques also have the capacity to do great damage to reef structures. The use of explosives or chemicals as well as some netting and trapping techniques damage coral substrate (examples, etc...)

References

Management

Generally, coral reefs exhibit an inverted biomass pyramid, made possible by the external recruitment of a number of larval fish species. In the past, management efforts have predominantly focused on bottom-up processes, including the importance of herbivorous fish populations on abating harmful algae growth. However, increased fishing pressure has altered trophic level interactions, necessitating the additional consideration of top-down processes when developing management strategies and practices. Some even advocate for management practices that have goals other than maximizing predatory and herbivorous fish stocks, focusing instead on higher cover of settlement-inducing crustose coralline algae to maintain the ecological and structural integrity of reefs. However, the most widely recommended policies are those that advocate for management with multiple goals on an ecosystem scale to predict and avoid possible cascading effects. In contrast, small-scale management practices are often made difficult and ineffective by the large-scale connectivity inherent in coral reef ecosystems, necessitating an increase in the scale of management, and specifically a network of interdependent reserves to maintain biodiversity.

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• Causes
  • Socioeconomic
    • Exploitation of coral reef fisheries is largely due to a high demand on the global market rather than the density of the local human population. (Cinner and McClanahan, 2006)
    • Overfishing cannot be quickly stopped because it is heavily tied to economic growth. Fishing pressure is increasing even as global catch declines (Bradbury, 2012)
• Effects
  • Food web
    • Herbivorous Fish
      • Dense populations of grazing fish and sea urchins abate harmful algae growth (Smith 2010)
      • Can have profound top-down ecosystem effects from removing top predators (Scheffer et al. 2005)
      • By fishing down the food chain, they too become overfished or die of diseases due to overcrowding (Jackson et al. 2001)
    • Algae/Corals
      • Excessive fishing of predatory fish leads to explosions in the populations of lower level consumers. These populations then overgraze on coralline algae and cause coral abundance to decrease (Stephens, 2012)
      • Can cause phase shift and eventual replacement of slow-growing corals by fast-growing seaweeds (Smith 2010)
      • Coralline algae reduced through cascading trophic effects that increase sea urchin populations (O’Leary et al. 2012)
      • Some species of algae are important for coral recruitment (O’Leary et al. 2012)
      • Overfishing causes indirect cascading effects on settlement
  • Physical effects
    • Coral structure can be physically damaged by netting and trapping techniques. Use of explosives and chemicals in fishing is more rare, but can also damage the corals and substrate (Jennings and Polunin, 1996)
    • Losses of biomass and abundance (Jackson et al. 2001)
    • Precursor for eutrophication, disease, and species introduction as it makes populations more vulnerable (Jackson et al. 2001)

References

Journal Articles

Anticamara, J.A., Watson, B., Gelchu, A., and Pauly, D. 2011. Global fishing effort (1950–2010): Trends, gaps, and implications. Fisheries Research 107(1-3): 131-136.

Cinner, J.E., and McClanahan, T.R. 2006. Socioeconomic factors that lead to overfishing in small-scale coral reef fisheries of Papua New Guinea. Environmental Conservation 33(1): 73-80.

Jackson, J.B.C., Kirby, M.X., Berger, W.H., Bjorndal, K.A., Botsford, L.W., Bourque, B.J., Bradbury, R.H., Cooke, R., Erlandson, J.,Estes, J.A., Hughes, T.P., Kidwell, S., Lange, C.B., Lenihan, H.S., Pandolfi, J.M., Peterson, C.H., Steneck, R.S., Tegner, M.J., and Warner, R.R. 2001. Historical overfishing and the recent collapse of coastal ecosystems. Science 293(5530): 629-638.

Jennings, S., and Polunin, N.V.C. 1996. Impacts of fishing on tropical reef ecosystems. Ambio 25(1): 44-49.

O’Leary, J.K., Potts, D.C., Braga, J.C., and McClanahan, T.R. 2012. Indirect consequences of fishing: reduction of coralline algae suppresses juvenile coral abundance. Coral Reefs 31: 547-559.

Roberts, C.M. 1997. Connectivity and management of Caribbean coral reefs. Science 278(5342): 1454-1457.

Scheffer, M., Carpenter, S., and de Young, B. 2005. Cascading effects of overfishing marine systems. Trends in Technology & Evolution 20(11): 579-581.

Valentine, J.F, and Heck, K.L. 2005. Perspective review of the impacts of overfishing on coral reef food web linkages. Coral Reefs 24(2): 209-213

Web Links
Bradbury, R. 2012. A World Without Coral Reefs. The New York Times. Web. <http://www.nytimes.com/2012/07/14/opinion/a-world-without-coral-reefs.html?_r=0>.

Human Impact on the Great Barrier Reef. University of Michigan. Web. <http://sitemaker.umich.edu/gc2sec7labgroup3/over-fishing>.

Smith, J.E. 2010. Coral Reef Loss: Determining the Importance of Overfishing and Nutrient Pollution in the Global Decline of Coral Reefs. National Center for Ecological Analysis and Synthesis. Web. <http://www.nceas.ucsb.edu/featured/smith>.