Role and history of fisheries
Fisheries means catching fish and other water animals, or raising them, for food and for money. Fish give protein, oil and vitamins. Millions of people earn a living from the sea.
How fishing changed
- Long ago: people used hands, spears and simple hooks near the shore.
- Later: nets and wooden boats with sails let them go further.
- Now: engine boats, steel nets, cold rooms, radio and satellite help. So the catch is bigger. That also means we must take care not to catch too much.
National fisheries and fishing vessels
Fisheries are of three kinds, by where they happen: coastal (small boats, a day trip), offshore (bigger boats, some days) and distant-water or ocean (large ships, weeks or months).
Fishing vessels also differ in size. A canoe or a small motor boat fishes near the shore. A medium boat can use trawl or purse nets. A large vessel carries a freezer, so the fish stay fresh for a long trip. Countries such as India, Japan and Norway all run all three kinds in their own way.
Marine environment and ecosystems
The marine environment is the sea water, the sea floor and everything that lives in them. An ecosystem is a place where living things and non-living things work together.
The food chain
Plankton are tiny floating living things. Phytoplankton are plant-like. They need sunlight, so they live in the top layer. Small fish and shrimps eat them. Big fish eat the small ones. Dead things sink and bacteria turn them back into food for plankton.
Different homes
Coral reefs, mangroves, shallow shelves and the open sea each hold different life. The key things that decide how much life there is: light, temperature, salt and nutrients.
Fishing grounds and surveys
A fishing ground is a sea area where many fish gather and can be caught well.
Where grounds appear
- Continental shelf: shallow sea, so sunlight reaches the floor and plankton grow well.
- Upwelling: wind and currents push surface water away, and cold deep water rises with nutrients.
- Where two currents meet: food gathers along the line.
How we find fish: surveys
A survey measures the sea to learn where fish are and how many. Tools: echo sounder (sound goes down, echo shows fish), test nets, water thermometers, and satellite maps of surface temperature and plankton colour.
Conserving the marine environment
If the sea gets sick, fisheries suffer. Main dangers: plastic and oil, sewage and farm fertiliser (they cause too much algae and the water loses oxygen), damaged reefs and mangroves, warming water and overfishing.
What helps
- Treat waste before it reaches the sea.
- Protect nursery areas such as mangroves and reefs.
- Make marine protected areas where fishing is not allowed.
- Fish only what the sea can replace.
Try it
In the 3D: go to the last step. Slide "Food in water" to 0, then to 10. Count the fish you see each time.
Predict first: will the fish number double if the food doubles? Check it.
At home: put a green leaf in a glass of clean water in the sun for a week, and another in a dark cupboard. Which water turns green? Green water means algae are growing, which is plankton-like life that needs light and food.
Key formulas and definitions
- Food chain: Sun → Plankton → Small fish → Big fish → People
- Fishing ground = enough Food (nutrients) + Light + the right Temperature
- Types of fisheries: coastal, offshore, distant-water
Worked examples
1. Write one food chain from the sea and say which part needs sunlight.
Phytoplankton → small fish → big fish → people. Only the phytoplankton use sunlight directly. They make food with it. All the other links get their energy by eating.
2. Why is there a good fishing ground where cold deep water rises?
Deep water holds many nutrients, because dead things sink and rot there. When it rises into the sunny top layer, plankton get both light and nutrients. They multiply, small fish come to eat them, then big fish come. So the area has many fish.
3. An echo sounder shows a thick band at 40 m depth. What does it tell the crew?
It tells them that a school of fish (or many plankton) is swimming near 40 m. The crew can place the net at that depth. A thicker band means a bigger school. Sound does not tell the fish kind, so they also use test nets.
Common mistakes
- Thinking the sea has endless fish. A stock can shrink if the catch is too big.
- Saying plankton are baby fish. Most plankton are tiny plants or tiny animals of their own kind.
- Thinking fish are found everywhere in the same number. They gather in rich areas such as shelves and upwelling zones.
- Thinking rubbish in the sea harms only the beach. It also harms plankton, fish and the people who eat them.