Wider Trawl Net Meshes Allow 22% of Catches to Escape, Aiding Sustainable Fishing

Contrary to the belief that bottom trawling nets "catch everything," new research from Taiwan's Fisheries Research Institute (FRI) reveals that adjusting mesh sizes can significantly improve the sustainability of fisheries. A study employing underwater imaging has demonstrated that widening the inner mesh of bottom trawls from the current 2 centimeters to 4 centimeters allows approximately 22% of fish catches to escape.

This finding is crucial for reducing the bycatch of less economically valuable fish, often termed "trash fish," and smaller individuals of commercially important species. By allowing these to escape, the adjustment helps conserve fish populations and supports the long-term viability of the fishing industry. The research was conducted in the waters off Yilan, using a double-layered net design with a 4 cm inner mesh and the standard 2 cm outer mesh.

Through underwater observation, the FRI team confirmed that fish remain mobile within the trawl net during operation and actively attempt to swim through the mesh. This observation provides scientific evidence that bottom trawling gear can be selective and reduce mixed catches. Zhang Yan-wei, an associate researcher at FRI, noted that previous estimates of escape rates relied on analyzing the retained catch, making it difficult to determine the survival rate of escaped individuals.

"Through direct observation with underwater imagery, we witnessed various fish and shrimp actively swimming during towing," Zhang explained. He added that smaller or more slender species are more likely to escape through the 4 cm mesh, while most major economic species remain within the inner net. The institute plans to conduct further trials in northern waters like Keelung.

The study suggests that adjusting the bottom trawl mesh size to 4 cm can contribute to sustainable fishery resources. The combination of mesh size adjustments and underwater observation offers a more precise understanding of the selectivity mechanisms in bottom trawl fishing gear, potentially leading to more responsible fishing practices.

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Through direct observation with underwater imagery, we witnessed various fish and shrimp actively swimming during towing. Smaller or more slender species are more likely to escape through the 4 cm mesh, while most major economic species remain within the inner net.