Fishing gear and methods
Each fishing method uses the fish's habits.
- Hook and line (long line, pole and line): bait draws the fish to a hook. Little by-catch (unwanted fish).
- Gillnet: a thin net wall. A fish pushes its head through, and the mesh holds it behind the gill cover.
- Purse seine: a long net ringed round a school near the surface. The bottom rope is pulled like a purse string.
- Trawl: a big cone-shaped net towed through the water or along the sea floor. The fish gather in the end bag (cod end).
- Traps and pots: fish or crabs enter but cannot get out.
- Lift and cast nets: thrown or raised from the shore or a small boat.
A method that catches only the wanted kind and size is selective. A method that catches everything is non-selective and often wastes small or non-target fish.
Main fisheries and resource enhancement
Some major fisheries are: small pelagic fish (sardine, mackerel, anchovy) caught mostly by purse seine; tuna by long line and pole and line; bottom fish (cod, prawn, flatfish) by trawl; squid with lights and jigs; seaweed and shellfish by collecting or farming.
Resource enhancement
Resource enhancement means helping stocks grow, not only taking from them. Examples: hatchery release (raise young fish in tanks and release them), artificial reefs (concrete or steel blocks that give shelter), seaweed and seagrass planting, and protecting nursery areas. They only work if the catch is also managed.
Structure and materials of fishing gear
A net is made of twine tied into meshes (holes). The mesh size is the length or gap of one hole. The net also has floats on top (to lift it), sinkers or lead weights at the bottom (to pull it down) and ropes to hold the shape.
Materials
- Natural fibre (cotton, hemp): cheap but rots.
- Synthetic fibre (nylon, polyester, polyethylene): strong, light, does not rot. Thin clear nylon (monofilament) is almost invisible in water, so it works well for gillnets.
- Steel wire for towing ropes and trawl doors (boards that spread the net).
Lost or old nets keep catching fish (ghost fishing) and make plastic waste. Recover and recycle them.
Fishing machinery, instruments and refrigeration
Machinery
A winch pulls ropes and nets. A net hauler or power block lifts nets. A line hauler pulls long lines. Cranes lift heavy catch.
Instruments
- Echo sounder / sonar: sound shows depth and fish.
- GPS and chart plotter: show position and where the net was set.
- Radio / satellite phone: weather and safety.
- Temperature sensor: finds warm and cold water edges where fish gather.
Refrigeration
Fish spoil fast in warm air. Ice (chilled water or flake ice) cools a short trip. Long trips use a refrigerated sea water (RSW) tank or freezer hold. Rule: chill early and keep it cold without a break.
Try it
In the 3D: go to step 4, then move the "mesh gap" slider. Count how many fish are caught and how many escape.
Predict first: if you double the gap, how many more fish escape?
At home: take a tea strainer and a kitchen sieve. Pour rice and lentils mixed together through each. Which one keeps the small grains? That is mesh size choosing what stays.
Key formulas and definitions
- A fish passes through if its body width < mesh gap; it is caught if width > gap
- Gear = twine (meshes) + floats (up) + sinkers (down) + ropes
- Cold chain: catch → ice or chill at once → keep cold without a break
Worked examples
1. Match the gear: (a) tows a cone-shaped net, (b) circles a school, (c) hangs as a net wall.
(a) trawl, (b) purse seine, (c) gillnet.
2. A net has a mesh gap of 4 cm. A young fish is 3 cm wide and an adult is 6 cm wide. Which one is kept?
The adult, 6 cm, is wider than the 4 cm gap, so it is kept. The 3 cm young fish fits through and escapes. This lets the young grow and breed.
3. Why is nylon better than cotton for a net?
Nylon is strong for its weight and does not rot in sea water. Cotton is cheap but rots, so it needs drying and replacing often.
Common mistakes
- Thinking a smaller mesh is always better. It also catches young fish and hurts the stock.
- Confusing gillnet and purse seine. A gillnet waits and fish swim into it. A purse seine is set round a school and then closed.
- Thinking cold storage is only for the port. Chilling must start on the boat.
- Forgetting that old nets keep killing fish and add plastic to the sea.