Why are fish stocks collapsing, and how can fishing and aquaculture be made sustainable?
The exploitation of wild fish stocks, the causes and consequences of overfishing, methods of managing fisheries sustainably, and the role and impacts of aquaculture.
A focused answer to AQA A-Level Environmental Science 3.5.2, covering the exploitation of wild fish stocks, the causes and consequences of overfishing, sustainable fisheries management, and the role and impacts of aquaculture.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
AQA wants you to describe how wild fish stocks are exploited, explain the causes and consequences of overfishing, describe methods of managing fisheries sustainably, and explain the role and environmental impacts of aquaculture. The recurring command words are Explain, Describe and Evaluate, so you must connect fishing pressure to population biology, not just name techniques.
Exploiting wild fish stocks
Modern fleets use large trawl and purse-seine nets, sonar to locate shoals, GPS, and factory ships that process catch at sea. This technology raises catch per effort far above what stocks can replace, which is why global catches plateaued and many stocks are now fully exploited or overexploited.
Causes and consequences of overfishing
A key population-biology point: as a stock shrinks, fishers often switch to smaller, younger fish, removing individuals before they can breed, which accelerates the decline. This is why mesh-size rules matter so much.
Sustainable fisheries management
Fisheries can be managed so stocks recover and stay productive:
- Quotas (total allowable catch) limit the tonnage of a species landed each year, ideally set at or below the MSY.
- Net mesh-size limits allow young fish to escape and breed at least once before they can be caught.
- Closed seasons protect fish during spawning so the next generation is produced.
- Marine protected areas ban or restrict fishing in nursery and breeding grounds, letting populations rebuild and spill over into adjacent fished waters.
- Licensing and effort limits cap the number and power of boats to prevent a race to fish.
Enforcement and international cooperation are essential because fish migrate across national boundaries, so unilateral limits can be undermined by neighbouring fleets.
Aquaculture
Aquaculture (fish farming) raises fish, shellfish or seaweed in ponds, tanks or sea cages and now supplies roughly half the fish humans eat. It can deliver large reliable yields and reduce pressure on wild stocks, but it has significant impacts:
- Water pollution from waste, uneaten feed, antibiotics and antifouling chemicals, causing local eutrophication.
- Disease and parasites (for example sea lice) building up in cages and spreading to wild fish.
- Escapes of farmed fish interbreeding with wild populations and reducing their genetic fitness.
- Demand for wild fish as feed, because carnivorous species such as salmon are fed fishmeal made from wild-caught fish, so farming them can still deplete wild stocks.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20185 marksExplain how a fishery can be managed so that wild fish stocks are harvested sustainably.Show worked answer →
A 5-mark Explain rewards a range of named measures, each linked to how it protects the stock. List alone caps the marks; the link is essential.
Maximum sustainable yield: harvesting at or below the maximum sustainable yield lets the population replace what is removed, so the stock stays stable.
Quotas (total allowable catch) cap the tonnage landed so catch does not exceed the surplus the population produces. Net mesh-size limits let immature fish escape and breed at least once, protecting recruitment. Closed seasons protect fish during spawning so the next generation is produced. Marine protected areas ban or limit fishing in nursery grounds, letting stocks rebuild and spill over into fished areas.
Top answers note enforcement matters: quotas only work if monitored, or stocks still collapse.
AQA 20226 marksEvaluate the use of aquaculture as a way of meeting the growing demand for fish.Show worked answer →
Evaluate needs benefits, drawbacks and a judgement. Markers expect both sides developed and a conclusion.
Benefits: aquaculture produces large, reliable yields, can reduce pressure on overfished wild stocks, supports coastal employment, and allows controlled feeding and harvesting.
Drawbacks: cage farms release waste, uneaten feed and antibiotics, causing local eutrophication; diseases and parasites such as sea lice spread to wild fish; escaped farmed fish interbreed with and outcompete wild populations, reducing genetic fitness; and carnivorous species such as salmon are fed fishmeal from wild-caught fish, so farming them can still deplete wild stocks.
Judgement: aquaculture eases pressure on some wild stocks but, for carnivorous species fed on wild fish, it can shift rather than solve the problem, so its sustainability depends on the species farmed and the management of waste and feed.
Related dot points
- The methods used to increase agricultural productivity, the environmental impacts of intensive farming, the differences between intensive and extensive and organic systems, and approaches to sustainable food production.
A focused answer to AQA A-Level Environmental Science 3.5.1, covering methods of increasing agricultural productivity, the environmental impacts of intensive farming, intensive versus extensive and organic systems, and sustainable food production.
- The economic and ecological value of forests, the causes and consequences of deforestation, and the methods used to manage forests sustainably including selective logging and replanting.
A focused answer to AQA A-Level Environmental Science 3.5.3, covering the economic and ecological value of forests, the causes and consequences of deforestation, and methods of sustainable forest management.
- The main water pollutants and their sources, the process and consequences of eutrophication, the use of indicator species and biological oxygen demand to monitor water quality, and methods of controlling water pollution.
A focused answer to AQA A-Level Environmental Science 3.4.3, covering the main water pollutants and their sources, eutrophication and its consequences, monitoring with indicator species and biological oxygen demand, and control methods.
- The meaning of sustainability and sustainable development, the concepts of ecological footprint and carrying capacity, the difference between renewable and non-renewable resources, and the principles that guide sustainable resource use.
A focused answer to AQA A-Level Environmental Science 3.6 sustainability, covering the meaning of sustainability and sustainable development, ecological footprint and carrying capacity, renewable and non-renewable resources, and the principles of sustainable resource use.
- The meaning of biodiversity at the genetic, species and habitat levels, how species and habitat diversity are measured and estimated, and the value of biodiversity to humans and ecosystems.
A focused answer to AQA A-Level Environmental Science 3.1.2, covering the three levels of biodiversity, the index of diversity, sampling and estimation, and the ecological and economic value of biodiversity.