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examBoard: Cambridge
examType: IGCSE
lessonTitle: Net Types and Mesh Size Regulations
Fishing nets are one of humanity's oldest tools for harvesting marine resources. Today, they remain the primary method for commercial fishing worldwide. However, with declining fish stocks and growing environmental concerns, understanding how different nets work and how they're regulated has become crucial for sustainable marine management.
Key Definitions:
Different fishing nets are designed for specific purposes, target species and fishing environments. Each has unique environmental impacts that need to be managed.
Large nets dragged through the water or along the seabed. They're shaped like a cone or funnel with a closed end (the cod end) where fish collect.
Types:
Environmental concerns: Bottom trawls can damage seafloor habitats and have high bycatch rates.
Large nets that hang vertically in the water with floats at the top and weights at the bottom.
Types:
Environmental concerns: Can accidentally catch dolphins, turtles and other protected species.
Vertical panels of netting that hang in the water, designed so fish swim into them and get caught by their gills.
Types:
Environmental concerns: High risk of bycatch and ghost fishing if lost.
Stationary nets that guide fish into a trap or enclosure.
Types:
Environmental concerns: Generally less harmful but can trap non-target species.
Mesh size is one of the most critical factors in determining what a net catches. Smaller mesh catches smaller fish, while larger mesh allows juveniles to escape while still catching mature fish.
Larger mesh sizes allow young fish to escape, ensuring they can grow to reproductive age and sustain the population.
Appropriate mesh sizes can reduce the capture of non-target species and undersized fish.
While short-term catches may be smaller, long-term yields increase as fish populations remain healthy.
Mesh size directly impacts which fish are caught and which can escape. This selectivity has profound effects on marine ecosystems and fish population dynamics.
When a fish encounters a net, several factors determine whether it will be caught:
Scientists use selectivity curves to show the probability of catching fish of different sizes with specific mesh sizes. These curves help fisheries managers set appropriate regulations.
In the early 2000s, North Sea cod stocks were severely depleted. As part of recovery measures, the EU increased minimum mesh sizes for cod fisheries from 100mm to 120mm. This allowed more juvenile cod to escape and grow to reproductive age. Combined with reduced fishing effort and closed areas, these mesh size regulations helped North Sea cod stocks recover from critical levels. By 2017, the fishery had regained enough sustainability to receive Marine Stewardship Council certification, though challenges remain.
Effective mesh size regulations require careful planning, monitoring and enforcement.
Fisheries scientists typically follow these steps:
Enforcing mesh size regulations presents several challenges:
Several approaches have proven effective in implementing mesh size regulations:
In UK waters, mesh size regulations vary by region and target species:
Post-Brexit, the UK has been developing its own fisheries management policies, including mesh size regulations.
The Mediterranean Sea faces particular challenges with mesh size enforcement. With 21 countries bordering the sea and many small-scale fisheries, coordination is difficult. Studies have shown that mesh sizes used are often smaller than regulations require. A 2018 study found that increasing trawl mesh size from 40mm (diamond mesh) to 50mm square mesh could reduce the catch of undersized fish by up to 44% while maintaining commercial catches. The General Fisheries Commission for the Mediterranean continues to work on harmonising regulations across the region.
Fishing technology continues to evolve, offering new opportunities for sustainable harvesting.
Recent innovations include:
As our understanding of marine ecosystems improves and technology advances, mesh size regulations will continue to evolve. The goal remains the same: to harvest marine resources sustainably while protecting the health and biodiversity of our oceans.
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