Performance of bycatch reduction devices varies for chondrichthyan, reptile, and cetacean mitigation in demersal fish trawls: assimilating subsurface interactions and unaccounted mortality

Abstract

To improve bycatch mitigation of chondrichthyans, reptiles and cetaceans for a tropical demersal fish-trawl fishery, species-specific responses to bycatch reduction devices (BRDs) were investigated using both in situ subsurface and onboard observations. There are few, if any, studies that have determined mitigation performances of BRDs from subsurface interactions for these species, as most are rarely encountered and thus require substantial levels of observer coverage for robust assessments. This study combined in-net and onboard (774 day trawls and 1320 day trawl hours of subsurface observer coverage) electronic monitoring on all fish-trawl vessels (n = 3) to compare bycatch mitigation performances among nine megafauna groups, based on escape rates and interaction durations for three BRDs over 6 months (June to December 2012). Overall, 26.9% of day trawls had no megafauna interactions and 38.3% of the 1826 interactions escaped, with most in rapid time (91.4% in ≤ 5 min). The upward inclined exclusion grid significantly improved the escape proportions for most chondrichthyans by 20–30%. All BRDs were highly effective in reducing reptile (turtles and seasnakes) bycatch, but irrelevant for the few sawfish (n = 13) that readily entangled in the anterior of the net. Cetacean (bottlenose dolphins only) interactions with BRDs were very rare (n = 7) despite high levels of attendance and depredation during trawling. Loss of targeted teleosts through the BRD hatch was rare (1.3% of day trawls). This relatively cost-effective method of electronic monitoring achieved very high levels of subsurface observer coverage (60% of day trawls or 56% of day trawl hours), and provided evidence that the subsurface expulsion of megafauna in poor condition is negligible. Furthermore, this study provides species-specific improvements toward bycatch mitigation strategies for demersal fish trawling.

Partitioning of diet between species and life history stages of sympatric and cryptic snappers (Lutjanidae) based on DNA metabarcoding

“…1, see trawl net configuration in Wakefield et al 32 ). Concurrently, catches of adult L. erythropterus and L. malabaricus (482 to 795 mm TL) taken by commercial fishers using demersal fish trawls (see trawl net configuration in Wakefield et al 33 ) in 52-58 m depth and ~60 km directly offshore from where the juveniles were sampled ( Table 1 & Fig. 1), were labelled and kept separate from the rest of the catch before collection approximately three days later by research staff.…”

Ecosystem-Based MSP for Enhanced Fisheries Sustainability: An Example from the Northern Adriatic (Chioggia—Venice and Rovigo, Italy)

“…The management of these new protection areas require a thorough application of systematic monitoring, also taking into account the seasonal variations of the Adriatic populations and accordingly applying adaptive management measures. The measures to be adopted for the fishing sector should aim at reducing the risks of interaction between fishing activities and the protected species/habitats, through spatial [80] and operational [81] limitations and specific technological improvements, such as Bycatch Reduction Devices (BRDs) [82,83], even on a seasonal basis. The new N2K site should also be appropriately managed through participatory governance between administrations and stakeholders, with awarenessraising and ad hoc training activities, also including research and monitoring activities.…”

DNA Barcode Reveals the Bycatch of Endangered Batoids Species in the Southwest Atlantic: Implications for Sustainable Fisheries Management and Conservation Efforts

“…To conclude, our results show the bycatch batoid species composition in the southwest Atlantic, which consist of some species under protection by national and international laws. In order to attenuate fishery impacts over biodiversity, managers should monitor and report catches at the species level, prohibit trade and landings of threatened and protected species, and manage bycatch to minimize mortality of non-target species with the adoption of new technologies aiming to mitigate bycatch [93,94,95]. Crucial to this process is the implementation of an accurate and standardized DNA-based species identification method, such as DNA barcoding, to improve and promote the sustainability of biodiversity, as well as to support the productivity of the fishery activity.…”