Sustainable fisheries — AQA GCSE Biology
Test yourself on Sustainable fisheries with AQA GCSE practice questions.
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Sustainable fisheries explained
Fish stocks are populations of fish that are harvested for food.
Read the full explanation
They are declining because humans catch fish faster than the populations can reproduce. Modern fishing fleets use sonar, large nets and factory ships, so they can locate and remove huge numbers of fish in a short time. As the breeding population shrinks, fewer young fish are produced, so the stock falls further. This is unsustainable because the ocean cannot replace the fish as quickly as they are removed. For example, if a cod population is reduced below the level needed for successful spawning, recruitment of young cod falls and the stock may not recover for many years. Understanding this decline is the first step towards managing fisheries sustainably.
It is important to maintain fish stocks at a level where breeding continues or certain species may disappear altogether in some areas.
A fish stock must be kept above a minimum size so that enough adult fish survive to breed successfully. If too many adults are removed, the remaining population may be too small or too spread out to find mates and spawn. Over time, the number of young fish falls, and the population cannot replace the fish that are caught. If this continues, the species may become locally extinct, meaning it disappears from that area even if it survives elsewhere. Maintaining stocks at a sustainable level means leaving enough breeding adults to produce the next generation. For example, if fishing removes most large adult cod before they can spawn, recruitment of young cod collapses and the local stock may disappear.
Control of net size and the introduction of fishing quotas play important roles in conservation of fish stocks at a sustainable level.
Two main methods help conserve fish stocks. First, controlling net size means using nets with a mesh large enough to let young, small fish escape while retaining larger adult fish. This allows juveniles to grow and breed before they are caught, supporting future recruitment. Second, fishing quotas set a limit on the number or mass of fish that can be caught from a particular stock in a given period. Quotas prevent too many adults being removed, so the breeding population remains large enough to reproduce. Together, these measures aim to keep the rate of fishing below the rate at which the stock can replace itself. For example, a quota might limit a fleet to a set tonnage of cod per year, while a larger mesh size reduces the catch of undersized cod.
Your focus
- State that fish stocks in the oceans are declining.
- Explain why overfishing causes fish stocks to fall.
- Describe how a reduced breeding population leads to fewer young fish.
Show all 9 objectives
- Explain why fish stocks must be maintained at a level where breeding continues.
- Describe how overfishing can cause a species to disappear from an area.
- Distinguish between local disappearance and global extinction.
- Describe how controlling net size helps conserve fish stocks.
- Explain how fishing quotas maintain fish stocks at a sustainable level.
- Compare the roles of net size and quotas in conservation.
Sustainable fisheries exam tips
Marking Points
- State that fish stocks are populations of fish that are caught for food and that their numbers are falling.
- Explain that the rate of fishing exceeds the rate at which fish populations can reproduce.
- Describe how improved technology, such as sonar and large factory ships, increases the number of fish caught.
- Explain that a reduced breeding population produces fewer offspring, so the stock continues to decline.
- Recognise that the decline is unsustainable because fish are being removed faster than they can be replaced.
- State that fish stocks must be kept at a level where enough adult fish survive to breed.
- Explain that breeding continues only if the breeding population is large enough to find mates and spawn successfully.
- Describe how removing too many adults reduces the number of young fish produced.
- Explain that continued overfishing can cause a species to disappear from a particular area.
- Recognise that local disappearance may occur even if the species still exists in other areas.
- State that controlling net size means using a mesh that allows small, young fish to escape.
- Explain that larger mesh sizes let juvenile fish survive to grow and breed, supporting future stocks.
- Describe fishing quotas as limits on the number or mass of fish that can be caught.
- Explain that quotas reduce the removal of adult fish so the breeding population remains sustainable.
- Recognise that both methods aim to keep fishing at a level the stock can replace.
Examiner Tips
- 💡Use the phrase ‘caught faster than they can reproduce’ to make the cause of decline clear.
- 💡Link the decline to human demand for food and advances in fishing technology.
- 💡When describing a consequence, refer to the breeding population and the number of young fish produced.
- 💡Use the term ‘breeding population’ when explaining why a minimum stock level matters.
- 💡Distinguish between local disappearance and global extinction if the question asks about ‘some areas’.
- 💡Link the idea of sustainable stock size to the survival of the next generation.
- 💡Name both methods and explain the effect of each on the fish population.
- 💡Use the terms ‘juvenile fish’ and ‘breeding adults’ to show which part of the population each method protects.
- 💡Link each method to the idea of keeping fishing below the rate of reproduction.
Common Mistakes
- Thinking that fish stocks decline only because of pollution; the main cause is overfishing, where fish are caught faster than they can breed.
- Confusing a fish stock with the total number of all fish species in the ocean; a stock is a particular population that is fished.
- Assuming that fish populations can always recover quickly; if the breeding population becomes too small, recovery may take many years or may not happen.
- Thinking that a species disappears everywhere at once; local extinction means it is lost from one area, not necessarily globally.
- Believing that breeding can continue normally even when very few adults remain; small, scattered populations may fail to reproduce successfully.
- Confusing the number of fish caught with the number of breeding adults left; it is the surviving breeding population that determines future recruitment.
- Thinking that smaller mesh nets are better for conservation; smaller mesh catches more young fish and harms future stocks.
- Confusing quotas with total bans; a quota allows a limited catch, whereas a ban prohibits fishing entirely.
- Assuming net size alone is enough; quotas and net size work together to protect breeding adults and juveniles.