Overfishing and managing fisheries Cambridge IGCSE Environmental Management revision
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In plain words
A fishing fleet with sonar and nets more than a kilometre long can find and catch almost every fish in a shoal. The sea used to be too big to empty. It no longer is, and the rules in this unit are the attempt to keep some fish for next year.
10 things to know
- Overfishing is catching fish faster than they can breed and replace themselves, so the population falls. Overharvesting is the same idea for other marine species.
- The target species is the one the boat is trying to catch. Its numbers fall, and when young fish are taken before they breed, the population cannot recover.
- Bycatch is the other species caught by accident, such as turtles, dolphins and sharks. Most are thrown back dead.
- Food chains are affected. Removing one species leaves its predators short of food and lets its prey increase.
- Limits on the size of boats and on the overall size of nets reduce how much each boat can catch. A larger mesh size lets small, young fish escape and grow to breed.
- Pole and line fishing is a sustainable method. Fish are caught one at a time, so there is almost no bycatch.
- Quotas limit the mass of each species that may be caught. Closed seasons ban fishing at certain times, usually the breeding season. The number of fishing days can also be limited.
- Protected areas are parts of the sea where fishing is banned, so stocks can recover and spread out. Conservation laws protect named species.
- International agreements are needed, because fish cross borders and much of the ocean belongs to no country. They work only with implementation and monitoring.
- Limitations. The sea is vast, so rules are hard to enforce and illegal fishing goes on. Fish over the quota are thrown back dead. Limits cut the income and jobs of fishing communities.
Worked example
A fish population is falling because young fish are caught before they can breed. Suggest two strategies and explain how each helps.
- Increase the mesh size of the nets: small, young fish swim through and survive to breed.
- Set a closed season during breeding, so the adults can lay their eggs without being caught.
- Both raise the number of young fish joining the population each year.
Tips and tricks
- Bycatch is not the fish you wanted in smaller sizes. It is other species caught by accident.
- For any rule, add how it is checked: inspections in port, observers on boats, satellite tracking. A rule that is not monitored does not work.
It lands in your notebook with its questions as flashcards.
Overfishing and managing fisheries: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is bycatch?
Turtles and dolphins in a tuna net are bycatch.
What is a quota?
Quotas cap the catch of each species.
Why is pole and line fishing sustainable?
Nothing unwanted is hauled in.
When is a closed season usually set?
Adults are left alone to reproduce.
What is the purpose of a protected area?
Stocks rebuild and spread into nearby waters.
A large predatory fish is overfished. What is the likely effect on the smaller fish it eats?Stretch
With fewer predators, more of the prey survive.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Overfishing and managing fisheries
Cambridge IGCSE Environmental Management 0680 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Define the term overfishing.[2]
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Catching fish faster than they can reproduce, so the population decreases.
Explain how increasing the mesh size of nets helps to conserve fish.[2]
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Small, young fish can escape through the larger holes. They survive to grow and breed, so the population is maintained.
Explain why international agreements on fishing are needed, and why they can fail.[3]
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Fish move between the waters of different countries, and much of the ocean belongs to no country, so one country acting alone cannot protect stocks. Agreements fail when countries do not sign or do not enforce them, because monitoring the open sea is difficult and costly.
Answers: Overfishing and managing fisheries
- 1. Catching fish faster than they can reproduce, so the population decreases.
- 2. Small, young fish can escape through the larger holes. They survive to grow and breed, so the population is maintained.
- 3. Fish move between the waters of different countries, and much of the ocean belongs to no country, so one country acting alone cannot protect stocks. Agreements fail when countries do not sign or do not enforce them, because monitoring the open sea is difficult and costly.