Course:EOSC270/2022/EOSC270/2022/Group 5 - Effects of Overfishing

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What is the problem? (Brenda)

What is overfishing?

Overfishing occurs when a fish species is harvested from a body of water at a rate where the population can no longer be sustained naturally. Among other threats to marine life, overfishing is a significant contributor to global population declines and the threat continues to increase due to insufficient commercial fishery management, consumer demand, and an inadequate number of protected areas[1].

There are three types of overfishing:

  1. Growth Overfishing Growth overfishing occurs when the population of average-sized fish are depleted, so fish that are smaller than normal are caught instead. In order to fill the same quotas that were in place when normal-sized fish were abundant, many more smaller fish will need to be caught. When larger fish are depleted, the remaining population will be smaller in size and delayed in sexual maturity. Fishing up great quantities of immature fish will cause the situation to become even more severe due to fish populations having less opportunities to spawn.
  2. Recruitment Overfishing Recruitment overfishing occurs when the mature adult population of a fish species is depleted to a level where it can no longer replenish itself naturally, as there are not enough individuals who have to reproductive capacity to produce offspring.
  3. Ecosystem Overfishing Ecosystem overfishing occurs when the structure of an ecosystem is altered by the effects of overfishing. When large predatory fish species are depleted, it results in small foraging species increasing in response which causes a shift in the ecosystem towards the smaller fish species[2].

The overall effects of overfishing include slower growth, lower reproductive rate, changes in ecosystem structure, and larger numbers of threatened and endangered species.

Motivations for Overfishing

For humans, fish are a low-cost source of protein and essential nutrients (e.g., omega-3 fatty acids, vitamins, and minerals). This leads to extensive overfishing caused by industrialization of fisheries for economic development and consumer markets[3]. When fishermen overfish, the fish population gets depleted which leads to a greater likelihood of overfishing the next year. Fishing is also a crucial source of income for families in many developing nations, especially those of low-income in rural areas where jobs are limited.

Affected Areas

Overfishing can occur in bodies of water of any size and is the most prevalent where wild catch is high (e.g., China, Peru, United States) as well as areas of illegal, unreported, and unregulated (IUU) fishing activity.

The distribution of wild fish catch by country for all commercial, industrial, recreational and subsistence purposes. Wild catch is measured by total seafood production minus aquaculture (FAO, 2018).

IUU fishing describes a variety of fishing activities and threatens efforts to conserve fish stocks. Illegal fishing is when fishing activities are conducted without the permission of the State or violates its laws and regulations. Unreported fishing refers to fishing activities that are either misreported or not reported at all to authorities. Unregulated fishing occurs in areas of no applicable conservation measures, where fishing activities are inconsistent with State responsibilities[4].

A fourth term, ghost fishing, depletes fish populations when marine organisms are captured by abandoned or lost fishing gear (i.e., nets) and causes “hidden fishing mortality” over a period of time.

Prevalence

The 2020 report published by United Nation’s Food and Agriculture Organization (FAO) show that the level of biological stock that can be sustainably fished decreased from 90% in 1974 to 68.8% in 2017[5]. Global fishing efforts are increasing at an alarming rate with emerging threats involving the expansion of fishing efforts into deeper waters, exploiting previously non-targeted species, and increases in capture rates.

The Impact of Overfishing on Marine Ecosystems (Amy)

The Impact of Overfishing

The global consequences of overfishing can be seen when investigating marine ecosystems in the open ocean. Overfishing causes the depletion of targeted species, but also affects surrounding species sharing the same ecosystem. Food chain disruption is the primary reason for this. As commercial fishing removes hundreds of thousands of fish from the ocean each day, there is less food for larger marine animals to survive on. This is caused by the depletion of secondary production due to the removal of prey[6]. Additionally, commercial nets often kill untargeted marine biota such as coral, sea turtles, and birds, while also being a major factor for the global declines in fish stocks [7]. As industrial fish harvesting methods evolve to make commercial fishing more efficient, marine ecosystems continue to suffer the consequences.

Food Web Disruption
An example of a marine food web with phytoplankton and zooplankton at the base of the web. When species are displaced, the food web is disrupted.

Overfishing disrupts the marine food chain and leads to a loss of important aquatic life. The imbalance of species population that occurs as a result of overfishing can be understood by analyzing various levels within the food web[8]. At the base of the food web are photoautotrophs which produce organic carbon for all marine life to survive. Examples of these species include phytoplankton, seaweed, and seagrass. The second level of the food web involves herbivores like zooplankton and sea urchins which obtain their food source from photoautotrophs in the ocean. The third level of the food web contains primary carnivores like squids, sardines, and other small fish which use herbivores as their main source of nutrients[9]. These fish are killed directly because of commercial fishing. When these fish are unable to reproduce at the same rate at which they are being captured and killed, the herbivorous species become overpopulated (as they are less preyed upon)[10]. At the top of the food web are the secondary carnivores. They contain a wide range of species including sharks, whales, and large fish. As the population of primary carnivores decrease due to overfishing, these top predators no longer have a sufficient nutrient source.  

Organisms Impacted

Certain organisms have unique characteristics that make them more vulnerable to being preyed upon. Prey vulnerability is dependent upon an organism's shape, mobility, color, and the ability to defend themselves. As certain species are captured by commercial nets, secondary carnivores search for different prey that can be easily hunted. For example, when forage fish are captured in substantial amounts during commercial fishing, their consumers need to hunt for other species to ensure they have sufficient nutrients[11]. Smaller, faster, and camouflaged organisms will increase their chances of living while slower and brighter coloured organisms will be easy to prey on.

Extent of Overfishing (Arthur)

Measurable changes to the ecosystem

Many species have become threatened by overfishing. Overfishing of key species in an ecosystem is a prominent anthropogenic effect on marine ecosystems. In particular, many species of sharks have been victims of overfishing and their absence have caused major shifts in their ecosystems. Large shark species are injured or killed to be used in shark fin soup, a delicacy in some asian countries. In a study conducted in 2007, shark populations on the eastern coast of America were overfished to the point that the population of their prey, cownose rays grew explosively. With the loss of their natural predator, cownose rays were able to increase in numbers without restriction. The unchecked ray population began eating so many scallops that shellfish underwent local extinction.[12] In another study, it was found that jellyfish outbreaks were increasing in frequency due to overfishing their natural competitors. In the Bering Sea, decreasing haddock populations correlated with a decade long incline for jellyfish abundance. Jellyfish outbreaks can cause loss of tourism, electrical and structural failure, and even human death in some cases. Had the competing fish species not been overfished, jellyfish species such as Chrysaora would not have been able to freely dominate their niche in the ecosystem. [13]

Past and present effects
Jellyfish bloom in Jellyfish Lake, Palau
Trawlers overfishing Cod

There have been many incidents of overfishing throughout human history. Efforts have been made by several countries to limit the amount of fishing that can be done to avoid depleting fish stocks across the globe. In 1989, the cod fishing industry in Newfoundland collapsed after cod stocks were depleted by being overfished during their spawning season. The Government of Canada intervened in 1992, closing the fishing industry in Newfoundland to protect the cod.[14] The declining stocks of fish around the world have also been detrimental to humans as well. In 2008, it was reported that fishing fleets around the world were losing approximately US$50 billion every year due to not being able to catch the amount of fish they had previously caught. [15]Reports in 2021 indicated that overfishing has caused the biomass of fish in the oceans to be reduced by nearly 60% since the 1800's. [16] There have been regulations put in place by the United Nations that aim to lessen or counteract the effects of overfishing, detailed in the United Nations Convention on the Law of the Sea (UNCLOS).[17] Several articles address overfishing directly, urging countries to impose restrictions and regulations on their fishing industries to prevent depletion of fish stock. Many fisheries have adopted the Harvest Control Rule (HCR) and similar models that limit the destructive effects overfishing causes to the ecosystem. [18]

Implications for the future

Even with many new regulations being imposed that attempt to quell the problems caused by overfishing, there remains opposition to these new policies. Primarily, there is a financial incentive that causes some people to want to fish more than the set restrictions, leading to illegal fishing activity that is hard to control.[19] Lobbying from the fishing industry and recreational fishers can also stop or obstruct policies that are meant to stop overfishing. Without government regulations or with prevalent illegal fishing, it is possible that fish stocks will be decreased to the point that populations of fish are unable to recover naturally. When larger fish stocks are depleted, smaller fish will be caught as a replacement. Larger amounts of smaller fish will need to be caught to match the amount of large fish that used to be caught, decreasing fish populatations even more.[20] However, the majority of fisheries recognize that sustainability of fish stocks is important and abide by their regulations. Fishing quotas and closed seasons are measures that contribute to the sustainability and possible regrowth of fish populations.

Given the impact, what are the solutions? (Antonio)

An example of aquaculture in a shallow body of water in Chile, South America. The danger of utilizing these nearshore fish farms is the potential for runoff waste, however, such serve as a unique opportunity to combat overfishing practices (Via Wikimedia)

Local Solutions:

Aquaculture/Mariculture & Fish Farming:

Aquaculture, the cultivation, and breeding of live fish in near-shore ponds and cages[21] is integral to the potential preservation of oceanic biodiversity, as it provides temporary local relief for commonly harvested aquatic species[22]. Conversely, the overgrowth of fish species in these near-shore ponds and cages may lead to the degradation of the local environment due to potential wastewater runoff[23] into shallow-water ecosystems, and this may halt the further expansion of aquaculture efforts in nations such as China[24] and Hong Kong. Due to this, implementations for controlling fish stocking rate and periodic shifting of cage locations (Including deeper water expeditions) have been explored[24], in order to increase the sustainability of the practice. Still, the implementation of mariculture provides a significant alternative to overfishing practices[25], as the fish are harvested sustainably, in a manner similar to livestock. Despite the logistical and potential ethical issues surrounding fish breeding, mariculture provides a controllable and feasible option to meet the large global demands for fish products, whilst simultaneously reducing the necessity for exorbitant bycatch in open-water fishing. Thereby, the practice allows for many overfished species to slowly return to sustainable numbers[22] in their natural habitat.

A map of the European Union's Economic Exclusive Zones (In Blue) - these are maritime extensions of a nation's area beyond its coastline - only the nation which controls the zone is legally obligated to utilizing the waters for fishing and other industrial purposes (Via Wikimedia)

International Solutions:

Co-Management:

Co-management is a growing practice globally, and is the collaborative arrangement between three forces – local communities, conservation groups, and governments[26] – it is viewed as a positive step towards lessening overfishing in economically important fishing regions. This strategy, involving the integration of local knowledge with scientific research is especially prosperous in developing communities with protected marine zones[26], as catches were ‘twice that’ of those which were obtained prior to the implementation of restrictions. Although co-management limits overfishing, it beneficially increases catch quality, as it allows for the reduction of epipelagic environmental stressors, thereby enabling fish populations to not be overwhelmingly depleted, resulting in healthy growth and maturity of oceanic species[27]. In essence, co-management serves to supply the high demand for fish in coastal communities through improving the quality – not the quantity – of the catch.

International Regulations & Exclusive Economic Zones:

In general, both national-level and international-level policy implementation and management may lead to the recovery of shrinking fish populations[28]. For instance, anchovy fisheries in British Columbia have been closely monitored monitoring since the early 2000s – Fisheries and Oceans Canada recommended studying biomass and distribution patterns of the species, eventually leading to strictly enforced threshold limits[29]. Across the world, laws were passed to rebuild fish stocks and end overfishing[30] – the most vital of these was the creation of exclusive economic zones, which banned foreigners from fishing within designated regions[31], limiting fish catch to locals. These implementations, in conjunction to continued sustainability research, have led to global fishery catch declines in many countries, including America and Bulgaria[31], as competition for resources was significantly reduced. Therein, at a global scale, the implementation of EEZs, coupled with national government desire to rebuild fish stocks – due to research in the field – has allowed for the passage of further restrictions and regulations on the fishing industry.

References

  1. ↑ Sadovy de Mitcheson, Yvonne J. (June 2020). "Over-fishing and under-management continue to threaten groupers so what now?". Marine Policy. 116.
  2. ↑ Shabouri, Bhram (2010). "Overfishing". 2nd International Conference on Chemical, Biological, and Environmental Engineering: 229–234.
  3. ↑ Mansfield, Becky (2010). ""Modern" industrial fisheries and the crisis of overfishing". Global Political Ecology: 98–113.
  4. ↑ "Illegal, Unreported and Unregulated (IUU) fishing". FAO.
  5. ↑ Lavadya, Naresh (November 2021). "Issues In Marine Capture Fisheries – An Overview". Just Agriculture. 2(3).
  6. ↑ Coll, Marta (December 2008). "Ecosystem Overfishing in the Ocean".
  7. ↑ Cooke, Steven J. (February 2006). "Contrasting recreational and commercial fishing: Searching for common issues to promote unified conservation of fisheris resources and aquatic environments".
  8. ↑ Frederiksen, Morten (November 2006). "From Plankton to Top Predators: Bottom-up Control of a Marine Food Web across Four Trophic Levels".
  9. ↑ "Marine Food Chain". National Geographic. April 2010.
  10. ↑ Pinto, Eva (March 2021). "Localized control of opportunistic, overabundant species in protected areas: a retrospective modelling approach encompassing future scenarios".
  11. ↑ Engelhard, Georg H. (January 2014). "Forage fish, their fisheries, and their predators: who drives whom?".
  12. ↑ Myers, Ransom (March 2007). "Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean". Science. 315: 1846–50 – via ResearchGate.net.
  13. ↑ Richardson, Anthony J. (June 2009). "The jellyfish joyride: causes, consequences and management responses to a more gelatinous future". Trends in Ecology & Evolution. 24: 312–322 – via sciencedirect.com.
  14. ↑ Kunzig, Robert (March 1995). "Twilight of the Cod". Discover. Retrieved 9 February 2022.
  15. ↑ Black, Richard (October 2008). "Fisheries waste 'costs billions'". BBC News. Retrieved 9 February 2022.
  16. ↑ Hatton, Ian A. (November 2021). "The global ocean size spectrum from bacteria to whales". Science Advances. 7 – via NCBI.
  17. ↑ "Text of the United Nations Convention on the Law of the Sea". un.org. Retrieved 9 February 2022.
  18. ↑ Rainer, Froese (October 2010). "Generic harvest control rules for European fisheries". Fish and Fisheries. 12: 340–351 – via Wiley Online Library.
  19. ↑ "Illegal Fishing". World Ocean Review. Retrieved 9 February 2022.
  20. ↑ Christensen, Villy. "Fishing Down the Food Web". American Fisheries Society. Retrieved 9 February 2022.
  21. ↑ Lai, Lawrence (1995). "The Hong Kong Solution to the Overfishing Problem: A study of the cultured fish industry in Hong Hong". Managerial and Decision Economics. 16: 525 – via Proquest.
  22. ↑ 22.0 22.1 Armah, A.K (January 2004). "Solutions for Sustainable Mariculture - Avoiding the Adverse Effects of Mariculture on Biological Diversity". Secretariat of the Conservation on Biological Diversity – via DesLibres.
  23. ↑ Zheng, Wei (15 April 2009). "Benefit and Cost Analysis of Mariculture based on Ecosystem Services". Ecological Economics. 68–6: 1626–1632 – via ScienceDirect.
  24. ↑ 24.0 24.1 Yu Feng, Yang (2005). "Development of Mariculture and Its Impacts in Chinese Coastal Waters". Rev Fish Biol Fisheries. 14: 1–10 – via Springer.
  25. ↑ Hannesson, Rognvaldur (2003). "Aquaculture and Fisheries". Marine Policy. 27–2: 169–178 – via DOI.
  26. ↑ 26.0 26.1 Guidetti, Paolo (2010). "Comanagement Practices Enhance Fisheries in Marine Protected Areas". Conservation Biology. 24: 312–318 – via JSTOR.
  27. ↑ Weeks, Rebecca (2013). "Comanagement of a Marine Protected Area Network in Fiji". Conservation Biology. 27: 1234–1244 – via JSTOR.
  28. ↑ Sanchez-Hernandez, Javier (24 August 2016). "Influence of a Minimum-Length Limit Regulation on Wild Brown Trout: An Example of Recruitement and Growth Overfishing". North American Journal of Fisheries Management. 36: 1024–1035 – via American Fisheries Society.
  29. ↑ Therriault, T.W (2002). "Review of Northern Anchovy Biology and Fisheries with suggested Management Options for British Columbia". Government of Canada.
  30. ↑ Abel, David (2 August 2018). "Law to Deter Overfishing seen at Risk". The Boston Globe. Retrieved 4 March 2022.
  31. ↑ 31.0 31.1 Keskin, Cetin (2 March 2017). "The Marine Fisheries in Bulgaria's Exclusive Economic Zone, 1950 - 2013". Frontiers in Marine Science – via ProQuest.
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