Management of the harvesting of marine species Revision Notes

Effective management of marine species harvesting begins with the choice of fishing gear and techniques tailored to target species while minimising environmental harm. Nets with larger mesh sizes allow smaller, juvenile fish to escape, reducing the risk of overfishing immature populations. For example, a trawl net with a mesh size of 50 mm will let young cod pass through, preserving future stock.

Species-specific methods such as pole and line fishing target particular fish like tuna with minimal bycatch. This method involves catching fish one at a time using a fishing rod and bait, which reduces the capture of non-target species and lowers habitat disturbance compared to large-scale netting. For instance, pole and line fishing is widely used in the Maldives to sustainably catch skipjack tuna.

• Larger mesh sizes protect juvenile fish by allowing escape.
• Pole and line fishing reduces bycatch and habitat damage.
• Selective gear supports sustainable fish populations.

To prevent overexploitation, fisheries management employs quotas that limit the total allowable catch for specific species. Quotas are based on scientific assessments of fish population sizes and reproductive rates. For example, a quota might restrict a fleet to catching no more than 10,000 tonnes of cod annually to maintain stock levels.

Closed seasons prohibit fishing during critical breeding periods, allowing fish to reproduce and replenish populations. For instance, the North Sea cod fishery has a closed season from March to May, coinciding with spawning.

Protected areas, such as marine reserves, restrict or ban fishing activities to conserve habitats and biodiversity. The Great Barrier Reef Marine Park in Australia includes zones where fishing is prohibited, protecting coral ecosystems and associated species. These areas serve as refuges that support fish stock recovery and spillover into adjacent fishing zones.

• Quotas limit catch to sustainable levels.
• Closed seasons protect breeding fish.
• Protected areas conserve habitats and biodiversity.
• Regulations balance fishing with conservation needs.

National conservation laws enforce sustainable fishing practices by regulating gear types, catch limits, and fishing seasons. These laws include penalties for illegal fishing and mechanisms for monitoring compliance.

Because many fish species migrate across national boundaries, international agreements are essential for coordinated management. Organisations like the International Commission for the Conservation of Atlantic Tunas (ICCAT) set catch quotas and conservation measures agreed upon by member countries.

Such agreements help prevent overfishing in international waters and ensure shared resources are managed sustainably. For example, ICCAT's quota system has helped reduce overfishing of bluefin tuna in the Atlantic Ocean.

• Conservation laws regulate fishing within countries.
• International agreements coordinate cross-border fisheries management.
• Enforcement and cooperation are key to sustainability.

Aquaculture supplements wild fish catches by farming species such as salmon, shrimp, and tilapia. It provides a controlled food source that can reduce pressure on wild stocks.

However, aquaculture can generate waste pollution, including uneaten feed and fish excrement, which may cause eutrophication in surrounding waters. For example, salmon farms in Norway have been linked to local nutrient enrichment and algal blooms.

Additionally, farmed species may escape and compete with wild populations or spread diseases. Habitat alteration, such as mangrove clearance for shrimp ponds, can degrade natural ecosystems. Effective management includes waste treatment, site selection, and disease control to mitigate these impacts.

• Aquaculture provides alternative food sources.
• Waste pollution can harm water quality and habitats.
• Escapes and habitat changes pose ecological risks.
• Sustainable practices are needed to minimise environmental damage.