5.4 Management of the Harvesting of Marine Species

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Why Do We Need to Manage Marine Harvesting?

The ocean contains enormous numbers of fish and other marine species (animals that live in the sea). For centuries, humans have caught these animals for food. However, as the world's population has grown and fishing technology has improved, we are now catching fish faster than they can reproduce (have babies and grow new populations). This is called overfishing.

When a species is overfished:

• Its population drops too low to recover easily.
• Other species that depend on it for food are also affected.
• The whole marine ecosystem (the community of living things in the ocean) becomes unbalanced.
• Fishermen eventually catch fewer and fewer fish, threatening their jobs and people's food supply.

To prevent this, governments, scientists, and international organisations have developed management strategies — rules and methods designed to allow fishing to continue while keeping fish populations healthy. The goal is sustainable harvesting: taking only as much as the ocean can replace naturally.

Strategy 1: Net Types and Mesh Size

How mesh size helps

• Small mesh size = tiny holes = the net catches everything, including very young, small fish that have not yet had a chance to reproduce.
• Large mesh size = bigger holes = small, young fish slip through and escape, while only larger, mature (fully grown) fish are caught.

By using nets with a larger mesh size, fishermen allow young fish to escape. These young fish grow up, reproduce, and keep the population stable. This ensures there will still be plenty of fish to catch in the future.

Types of nets and their environmental impact

Different net types have different effects on the marine environment:

• Drift nets — Long nets that float near the surface and catch whatever swims into them. They can accidentally trap non-target species such as dolphins, turtles, and seabirds. These accidental catches are called bycatch (animals caught that were not the target). Drift nets are now banned or heavily restricted in many countries.

• Trawl nets (trawling) — Large nets dragged along the seafloor or through the water by a boat. Bottom trawling is particularly destructive because it drags across the seabed, destroying coral reefs, sponges, and other habitats. It also catches large amounts of bycatch.

• Purse seine nets — Circular nets that are drawn closed at the bottom like a purse to trap a whole school (group) of fish near the surface. These can be more targeted but can still accidentally trap dolphins.

• Fixed nets / gill nets — Nets set in one place that trap fish when they swim into them and get caught around their gills (the breathing organs of a fish). These can also cause bycatch problems.

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