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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. 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 sea snake) bycatch, but irrelevant for the few sawfish (n = 13) that readily entangled in the anterior of the net. Cetacean (bottlenose dolphins, Tursiops trunactus, 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.

Two types of depredation mitigation devices (DMD) were designed and tested aboard pelagic longline fishing vessels targeting tunas and swordfish off the Seychelles. The DMDs were designed to reduce the damage and removal of fish from the fishing gear by predators such as toothed whales and sharks. The first DMD was termed "spider" and was made up of a 100 mm diameter plastic disc with sixteen holes in its outer range and a 37 mm diameter central hole.  Eight 1200 mm long hanging legs were created by placing four polyester strands into the outer holes and the entire system is triggered by a biting fish.  The second DMD, "sock", was designed to cover the fish to hide it from predators through either a net made up of fiberglass mosquito netting or of propylene fiber net.  Shark depredation was significantly higher throughout the surveys than toothed whale depredation, but toothed whales caused more damaged to fish through depredation events. The sock DMD did not affect the catch rates of targeted species or depredation events by either sharks or toothed whales.  These results for the spider DMD were not presented. Trigger rates for the two DMDs were up to 87.3% for the spider and 69.2% for the sock.  The protection rate was as high as 80% for spider but only 15.5% for the sock. Entanglement rates of the DMDs with the fishing gear were low for the spider (3.6%) and higher for the sock (17.8%).  In addition, the use of these DMDs significantly slowed down the fishing process, and therefore additional work into the design and application of DMDs needs to be explored.

The Dolphin Wall Net (DWN) was designed by these fishermen to reduce dolphin attacks during fishing operations in Kerala, India. Specifically, humpbacked dolphins (Sousa chinensis) tend to congregate in fishing areas, surrounding the ring seine net and removing fish from the net.  This net design can be used by fishermen instead of crackers, which can cause harm to the dolphins. The authors provided fishermen from four stations in Kerala, India (Kasargode, Kozhikode, Ernakulum and Kollam) questionnaires to fill out. The questionnaires were designed to collect information on ring seine fishing operations, dolphin attacks and the structural details of the DWN when it was used.  The authors presented results on the structure of the DWN used by these fishermen but did not report any information regarding differences in bycatch rates between regular ring net operations and those using DWN.

Incidental captures of the franciscana dolphin (Pontoporia blainvillei) by artesinal coastal fishermen of Buenos Aires, Argentina were investigated. Data was collected on carcasses of 54 incidentally captured dolphins between 2003 and 2009. Results indicated that the majority (69%) were animals four years old and younger, 74% of entangled animals were sexually immature and 85% were physically immature. Entanglements were not associated with any disease or physiological disorder. No bycatch mitigation techniques were tested for this paper.

A modified single-layer codend configuration developed from previous studies was evaluated using BRDs with guide net angles of 30° and 45°. For target species, catch loss rates based on the number and weight of individuals were 9% and 13%, respectively for herring (Culpea pallasii) with the 30° guide net and 16% and 18% with the 45° guide net. For Korean pomfret (Pampus echinogaster), catch loss rates were 24% and 23% at 30° and 4% at 45°. Catch loss rates of target mackerel (Scomber jamponicus) with the 30° guide net reached 56%, whereas hairtail (Trichiurus lepturus) had loss rates of 60% and 65% with the 45° guide net. These results suggest that further modification of BRD is necessary. However, no bycatch of marine mammals occurred during the experimental operations, despite dolphins being observed nearby.