In pomfret netting, reducing the rate of bycatch of non-target fish species is crucial for protecting marine biodiversity and achieving sustainable fisheries development. Bycatch not only leads to the death of non-target species but can also disrupt ecological balance and affect the long-term utilization of fishery resources. Therefore, a comprehensive approach is needed, encompassing gear design, operational methods, technical assistance, and management strategies, to reduce bycatch.
Optimizing gear design is fundamental to reducing bycatch. Traditional pomfret nets have small mesh sizes, easily catching juvenile fish and non-target species. Increasing the mesh size allows smaller fish and non-target species to escape more easily while preserving the target pomfret. Furthermore, using selective net materials, such as more elastic netting lines, can reduce the crushing damage to fish during towing, lowering the mortality rate of non-target species. The application of separation grids and square nets can further enhance the gear's ability to distinguish between target and non-target organisms, guiding non-target species away from the net.
Improving operational methods is also essential for reducing bycatch. During trawling operations, controlling the trawling speed and depth can avoid excessive disturbance to bottom-dwelling fish and reduce the passive entanglement of non-target species. For example, operating above the water column where non-target fish inhabit, or adjusting the trawling time to avoid their active periods, can significantly reduce the bycatch rate. Furthermore, adopting a "one net, multiple bags" design, where multiple smaller bags are placed in front of the main bag, allows for graded capture based on fish size and species, facilitating the subsequent release of non-target species.
The application of technological aids provides innovative solutions for reducing bycatch. Acoustic repellent devices emit sound waves of specific frequencies to drive away easily bycatch species such as dolphins and turtles, reducing their contact with the net. Magnetic devices utilize the sensitivity of cartilaginous fish like sharks to electromagnetic fields, placing magnets nearby to guide them away from the trawl area. The installation of underwater camera systems allows for real-time monitoring of the fish composition within the net, providing fishermen with information to adjust their operations and release non-target species promptly.
Improving fishing gear technology is key to reducing the bycatch rate. Improving net structure, such as adding escape hatches or buoyancy devices, can provide escape routes for non-target species. For example, an automatically opening escape hatch at the top of the net can allow a non-target species to escape due to changes in water pressure. Furthermore, using biodegradable net materials can reduce the long-term threat of abandoned nets to marine life and lower the probability of "ghost fishing."
Improved management strategies provide institutional guarantees for reducing bycatch. Implementing a fishing quota system to limit the intensity and scope of trawling operations can prevent resource depletion and increased bycatch caused by overfishing. Simultaneously, establishing a bycatch monitoring and reporting mechanism, requiring fishermen to record the types and quantities of bycatch species, provides data support for scientifically assessing the impact of bycatch. In addition, strengthening fishermen's training to improve their awareness of bycatch issues and encouraging the use of selective fishing techniques are also important ways to reduce bycatch rates.
International cooperation and experience exchange are of great significance in promoting the reduction of bycatch. Fishery resource conditions and bycatch issues vary across different sea areas. Sharing successful cases and technical experiences can promote collaborative development in global fisheries management. For example, the open-top-plate behavior-based bycatch reduction device used in shrimp trawls in Nordic countries has effectively reduced the bycatch rate of juvenile red snapper. Its design concept and technical methods can provide a reference for pomfret net operations.
Reducing the bycatch rate of non-target fish species in pomfret net operations requires a comprehensive approach encompassing gear design, operational methods, technical assistance, management strategies, and international cooperation. Through continuous innovation and scientific management, it is possible to ensure the economic benefits of fisheries while minimizing negative impacts on marine ecosystems, thus achieving sustainable development of fisheries.
