Applying Fish Behavior to Reduce Trawl Bycatch: Evaluation of the Nested Cylinder Bycatch Reduction Device

Abstract

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.

Performance of the Nordmøre Grid in Shrimp Trawling and Potential Effects of Guiding Funnel Length and Light Stimulation

“…However, placing LEDs around the escape exit was ineffective at stimulating fish escape through the grid escape exit. Based on the results obtained, it appears that LEDs discourage fish from getting close to the area where they are placed, which agrees with the results of Parsons et al (2012) and seems to apply especially to species such as Haddock, whose escape behavior is known to be directed upwards (Winger et al 2010;Sistiaga et al 2016). Therefore, placing the LEDs at the lower part of the Nordmøre grid could be a better option, as it can direct the fish toward the escape exit without contacting the grid first.…”

Reducing bycatch in the United States Gulf of Mexico shrimp trawl fishery with an emphasis on red snapper bycatch reduction

“…This was not anticipated since the effect of the sock is to displace the entire catch deeper into the trawl bag, thus requiring all bycatch species to swim further up-stream to exit the trawl. Previous work on this device (Parsons et al, 2012) likewise demonstrated decreased total bycatch reduction as sock length increased. Although we had no data available for snapper bycatch using the longest sock reported in this study, the apparent lack of a significant effect on red snapper bycatch observed in this study is possibly due to the strong rheotactic behavior observed in red snapper in laboratory studies.…”

“…The nested cylinder bycatch reduction device (NCBRD), developed using laboratory behavioral studies (Parsons and Foster, 2007;Parsons et al, 2012), was herein evaluated for reducing bycatch in shrimp trawl fisheries and for its application in the U.S. Gulf of Mexico (GOM) fishery. We examined the efficacy of the NCBRD for retaining shrimp, for reducing total bycatch, and for reducing bycatch of juvenile red snapper (Lutjanus campechanus), a species that is presently over-fished in the GOM.…”

Effects of diel period and diurnal cloud cover on the species selection of short and long penaeid trawls

“…Similar concepts have been applied to behavioural-type BRDs in codends (e.g. Parsons et al, 2012) and are supported by other studies examining the effects of contrasting panels to modify the visual stimulus of fish and promote their escape through meshes (Glass and Wardle, 1995;Gray et al, 2000). If any such subtle modifications can be included within existing trawl designs (and not as additional BRDs), this might facilitate their adoption.…”