Marine harvesting and aquaculture
Explain how harvesting affects target and bycatch species and food chains, then weigh aquaculture and management options.
This original StudyForA sequence supports Cambridge IGCSE Environmental Management 0680 Topics 1–4 for exams in 2027, 2028 and 2029. Named local examples are chosen by the learner and centre; verify current conditions and local context with reliable sources. It is not a Cambridge paper, official grade or complete course.
Before you begin
- Use the 2027–2029 syllabus and check your exam year and centre's entry arrangements. Topics 1–4 are taught on this page; Topics 5–7 are still being built.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which item is a marine-harvest management strategy in the syllabus?
What you will learn
- Explain how harvesting affects target and bycatch species and food chains, then weigh aquaculture and management options.
- Use evidence from an unfamiliar case to explain a cause-and-effect link and justify a suitable response.
Trace effects of marine exploitation
Overfishing and overharvesting reduce populations of marine species. Harvesting can affect target species and bycatch species caught unintentionally, with changes moving through food chains when predators or prey become less available.
Describe the links in context: a change in one population can affect organisms that feed on it or are eaten by it. Avoid predicting the exact direction without information about the food web.
Evaluate marine aquaculture
Marine aquaculture is farming marine species in captivity; the syllabus groups include fish, crustaceans and seaweeds. It can reduce pressure on natural fisheries and increase food supply.
Potential effects include escapes, disease, altered local food webs, nutrient enrichment from waste, energy use and the source of feed. Weigh these against the wild harvest avoided and the amount and type of food produced.
Compare harvest-management strategies
Strategies include limiting boat or net size, increasing net mesh size, pole-and-line methods, quotas, closed seasons, limits on fishing days, protected areas, conservation laws and international agreements with implementation and monitoring.
Rules can help when they match the species and are monitored, but costs, compliance, displaced effort and cross-border enforcement can limit results. Compare ecological recovery with effects on livelihoods and food supply.
Sources for this lesson
Pause and explain
What is one possible aquaculture limitation to evaluate?
Worked example
A fishery reports fewer target fish and a high bycatch rate. Explain one ecosystem concern and recommend two management strategies with a limitation for each.
Show the worked solution
- Lower target populations can affect predators and prey in the food chain; bycatch can reduce non-target populations too.
- Larger mesh can let smaller organisms escape, but species and net design matter.
- Quotas or closed seasons can limit harvest, but require monitoring and may affect livelihoods or shift fishing effort.
Answer Overharvesting can reduce target and bycatch species and alter food chains. Mesh rules and quotas or closures may help, but effects depend on enforcement, design and how effort changes.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
An aquaculture site increases food supply but reports fish escaping and nutrients in nearby water. Explain two benefits and two risks that a manager should compare.
Give me a hint
Use food supply and pressure on fisheries alongside ecological effects.
Compare my reasoning
- Aquaculture can increase food available to people and reduce exploitation of natural fisheries.
- Escapes may affect local food webs, while waste can enrich nearby water with nutrients.
- Compare scale, species, monitoring and feed source to decide whether benefits outweigh the site risks.
The site may provide food and reduce wild harvest, but escapes and nutrient waste can harm local ecosystems. A judgement needs site-specific evidence and management performance.
Look for these in your work
- Two benefits considered
- Two risks explained
- Evidence-based evaluation
A fishery has a seasonal breeding period and a high catch of young fish. Compare a closed season with a larger net mesh and give one implementation issue for each.
Give me a hint
One controls timing; the other changes which organisms can be caught.
Compare my reasoning
- A closed season can protect the fishery during the breeding period, but effort may shift to other periods or areas.
- Larger mesh can allow smaller fish to escape, but enforcement and gear adaptation need monitoring.
- Compare both strategies with population, bycatch and livelihood evidence.
A closed season protects a time window; larger mesh changes capture size. Both may help, but monitoring, compliance and displaced fishing effort affect results.
Look for these in your work
- Strategies distinguished
- Implementation issue for each
- Population and livelihood evidence included
A government considers quotas, protected areas and an international agreement for a shared fishery. Design two measures of success and one sign that enforcement needs improvement.
Give me a hint
Track ecological outcomes and compliance, not just the number of rules written.
Compare my reasoning
- Measure target and bycatch population trends or evidence of recovery inside and outside protected areas.
- Track catch against quotas, fishing days and compliance across participating areas.
- Repeated breaches or effort displaced to unmonitored locations would suggest enforcement or international coordination needs improvement.
Success should include population and bycatch trends plus compliance with agreed limits. Breaches or fishing shifted beyond monitored waters signal the need for stronger implementation and cooperation.
Look for these in your work
- Ecological outcome measured
- Compliance measured
- Enforcement signal identified
Common mistakes
- Treating bycatch as the target species
- Assuming aquaculture has no environmental effects
- Recommending quotas without implementation or monitoring
- Ignoring livelihood effects in a management discussion
What can you explain now?
What is marine aquaculture?
Compare with the explanation
Farming marine species in captivity
The correct answer is “Farming marine species in captivity”. The alternatives “Harvesting only wild fish with a net” and “Treating seawater in a desalination plant” do not match the syllabus concept. Explain how harvesting affects target and bycatch species and food chains, then weigh aquaculture and management options.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain one effect of overharvesting, then compare an aquaculture benefit and one harvest-management strategy with its limitation.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.