Applying Fish Behavior to Reduce Trawl Bycatch: Evaluation of the Nested Cylinder Bycatch Reduction Device
We used a laboratory flow chamber to examine the behavioral response of juvenile red snapper, Lutjanus campechanus, to hydraulic and illumination changes with the intention of exploiting these responses to devise a more effective bycatch reduction device (BRD). Snapper were observed to use slack water areas for flow refuge, and this refuging behavior increased the chance of the fish escaping from the flow chamber. Additionally, we observed that dark-adapted red snapper were more likely to exit the test chamber when the flow chamber was illuminated during nighttime hours. We also observed a significant effect of illumination intensity on the time required for red snapper to locate and exit the flow chamber. These behavioral observations were then used to design a BRD that was tested in the Gulf of Mexico shrimp trawl fishery on board a commercial fishing vessel. The Nested Cylinder Bycatch Reduction Device (NCBRD) employed flow blocking plates to encourage fish to move into an area of the trawl where they could more easily escape. The NCBRD reduced total fish bycatch by about 53% and retained 81% of shrimp. Modifications of the inner cylinder of the NCBRD provided higher shrimp retention rates (86.2%-96.6%) but lower bycatch reduction rates (37.2%-42.9%). Illumination of the NCBRD during field testing had no significant effect on total fish bycatch or shrimp retention. However, we found that red snapper bycatch was reduced by 50% when the NCBRD was illuminated. These results suggest that illumination may be effective for increasing the performance of a BRD’s ability to exclude red snapper and perhaps other species.
Document Type: Research Article
Publication date: 2012-05-01
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