Effective use of the sea
People use the sea in many ways: food (fishing, fish farming, seaweed), transport (ships and ports), energy (offshore wind, oil, gas, tides), materials (salt, sand), tourism (beaches, diving, boating) and research. Different users need the same space, so they can clash: a wind farm and a fishing ground, or a harbour and a coral reef.
Effective use means sharing and planning: map who uses what, set zones, use gentle methods and measure results.
Sustainable catch
A fish population grows each year. A sustainable catch takes no more than that yearly growth. Take more and the stock falls, next year there is less growth, and the fall speeds up. This is overfishing. Tools to avoid it: catch limits, closed seasons, minimum fish size, net-mesh rules and licences.
Nature conservation
Conservation means protecting nature while still using it wisely. Important places: coral reefs, mangroves, seagrass beds and tidal flats. They are nurseries for young fish and they shield the coast from waves.
Marine protected areas are zones where fishing and building are limited or banned. Fish inside grow bigger, make more babies and spread to nearby waters.
Threats to the sea
Main threats: overfishing, plastic and waste, oil and chemical pollution, farm fertiliser washing in (which makes too much algae), damage from boat anchors and nets, and warming water that bleaches coral. Each of us helps by choosing sustainable seafood, avoiding single-use plastic and joining beach clean-ups.
Try it
In the 3D, set protection to 0 and push fishing effort to maximum. Note the fish percent. Now raise protection to 30 and compare. Predict first, then check. At home, list five sea products you use in a week and ask where they come from.
Key formulas and definitions
- Sustainable catch ≤ yearly growth of the stock
- Yearly growth = stock × growth rate
- Protected share (%) = protected area ÷ total area × 100
- Key terms: overfishing, nursery, marine protected area
Worked examples
1. A stock of 1000 tonnes grows 10% a year. What is the sustainable catch?
Growth = 1000 × 0.10 = 100 tonnes. A sustainable catch is at most 100 tonnes a year.
2. Fishers take 150 tonnes from that stock in one year. What happens to the stock?
100 grow back, 150 are taken, so the stock falls by 50 tonnes to 950 tonnes. Repeated each year the fall grows.
3. A bay of 200 km² protects 30% as a no-take zone. What area is protected?
200 × 30 ÷ 100 = 60 km².
4. Of 40 sea users in a survey, 10 are fishers, 12 tourism and the rest shipping. How many shipping users?
40 − 10 − 12 = 18.
Common mistakes
- Thinking the sea is endless, so any amount can be taken.
- Thinking protected areas hurt fishers. Fish spill over and catches nearby often rise.
- Counting only fish. Reefs, mangroves and seagrass are the nurseries.
- Believing pollution far inland does not reach the sea. Rivers carry it.