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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.

Tests were conducted aboard Canadian longline vessels targeting swordfish (Xiphias gladius) to determine if there were differences in the catch rates and size composition of swordfish and bycatch species caught by monofilament and multifilament nylon gangions.  No significant differences in the mean lengths of swordfish were found between the two nylon gangions but catch rates did differ significantly, with more swordfish caught on the monofilament gangions. There was also a significant difference in catch rates between the two gangions for blue sharks (Prionace glauca) and pelagic stingrays (Dasyatis violacea), with more animals caught on monofilament gangions. There was no significant difference in catch rates between gangions for mako sharks (Isurus oxyrinchus), white marlin (Tetrapturus albidus) or loggerhead sea turtles (Caretta caretta).

Neodymium-iron-boron (Nd2Fe14B) permanent magnets were used to test behavioral responses in spotted catsharks (Scyliorhinus canicula) and thornback skates (Raja clavata). Both species significantly avoided the Nd2Fe14B magnets more often in comparison to the control and procedural control and they fed significantly more from the control and procedural control in comparison to the magnets. The study also demonstrated a correlation between avoidance speed and distance with water temperature. 

Circle hooks and J-style hooks were tested on pelagic longline vessels (US Atlantic) to determine if the use of circle hooks reduced bycatch mortality while maintaining target species catch rates.  0⁰ offset circle hooks were determined to increase the survival of bycatch species at haulback while having little impact on target species catches.  Specifically, J-style hooks had a significantly higher total overall catch rate.  Catch rates of yellowfin tuna (Thunnus albacares) in the fall were higher (significantly) for circle hooks and pelagic stingrays (Pteroplatytrygon violacea, spring caught) were the only species that had a significantly higher catch rate on J-style hooks. Circle hooks caught four times as many yellowfin tuna in the mouth compared to J-style hooks.  Yellowfin tuna and dolphinfish (Coryphaena hippurus) caught on circle hooks in the fall and spring respectively, were significantly larger than those caught on J-style hooks.  Survival rates of dolphinfish and escolar (Lepidocybium flavobrunneum) were statistically higher at haulback when circle hooks were used in the fall and spring respectively. 

A literature review of 30 studies was conducted to determine the  effectiveness of various bycatch reduction devices for elasmobranchs. The risk of capture was 1.2 times higher on circle hooks but haulbaulk mortality as well as deep hooking was reduced. Wire leaders had higher shark catch and haulback mortality rates compared to monofilament. Hooking position is determined by the hook shape and width combined with bait. These characteristics also affect the ability to sever monofilament leaders. Shark catch rates and deep hooking were increased when fish was used for bait compared to squid. Wider hooks resulted in reduced pelagic stingray (Pteroplatytrygon violacea) catch and mortality.

Tests were conducted aboard pelagic longline vessels fishing off the coast of Uruguay, to determine the effect of hook type (circle hook vs J-hook) on the catch and length composition of target and non-target species.  Both American and Spanish style longlines were used during these experiments.  American style longlines consist of a 3.6 mm polyamide monofilament mainline with polyamide or polyester buoys lines 9-36 m long.  Spanish style longlines consist of 5-mm polyethlene multifilament mainline with buoy lines (similar in thickness and material to mainline) 12-18 m long.  On the American style longlines, albacore tuna (Thunnus alalunga) and shortfin mako shark (Isurus oxyrinchus) catches were significantly higher on circle vs J-hooks. Catches of other tunas and sharks (blue (Prionace glauca) and porbeagle (Lamna nasus) were also higher on circle hooks, but were not significantly higher.  There was no significant difference in the catches of seabirds or sea turtles between the two types of hooks on the American style longlines.  On the Spanish style longlines, albacore tuna catches were also significantly higher on circle compared to J-hooks, and there was a significant decrease in pelagic stingray (Pteroplatytrygon violacea) catches on circle hooks.  No significant difference in the catch rates of seabirds or sea turtles was seen between the two types of hooks on this type of longline.  There was no significant difference in the length distribution for any species between the two hook types on either type of longline.  There were also no significant differences between hook types for any hooking location of incidentally caught sea turtles.

An observer program assessed the impact of the Costa Rican longline fishery on bycatch species from 1999 to 2010. Observers recorded species, sex, reproductive state, and dimensions of all animals captured. They also recorded information about individual longlines, including location, set and haul back times, hook type, hook number, bait used, target species, and total number of hooks. The longline fishery caught a large number of silky sharks (Carcharhinus falciformis), olive ridley turtles (Lepidochelys olivacea), and pelagic stingrays (Pteroplatytrygon violacea). The authors estimate that 699,600 olive ridleys were caught between 1999 and 2010, including 92,300 adult females. The captures correspond with a decline in nesting populations nearby and statistically significant size decreases in mature turtles. They also observed a decline in the average size of silky sharks. Geospatial analysis of the data indicated that there were temporal shifts in mahi-mahi (Coryphaena hippurus) abundance, but fishing efforts did not shift with abundance. The authors suggest marine protected areas and/or time area closure to reduce the bycatch of sea turtles and sharks.  

Two new types of turtle excluder devices were tested in the Northern Australia prawn fishery to determine their ability to exclude sea turtles from capture.  The first design, JT 1, had a large escape opening across the width of the top panel ahead of the codend, with the forward edge of the escape weighted down and the aft edge buoyed.  This design did not prevent the capture of sea turtles or other large sharks and rays but caught 6.6% more tiger prawns (Peneaus sp.) and 10.5% more endeavour (Metapenaeus sp.) prawns than the standard net.  The second design, JT 2, had two large holes (200 cm long x 30 meshes deep) cut into the side panels of the net ahead of the codend with the aft edge weighted and two standard (40 mesh wide) bigeye escape panels were added between the two side openings.  The second design also did not prevent the capture of sea turtles or other large sharks and rays but did reduce finfish bycatch by 5% and caught 5.2% more tiger prawns and 6.9% more endeavour prawns compared to standard nets.

A cumulative impact analysis framework integrating species habitat suitability and fishing effort data, stratified by gear type, was used to assess bycatch risk for threatened and protected species in China's seas and adjacent waters. Across all taxonomic groups examined, including seabirds, sea turtles, marine mammals, elasmobranchs, bony fishes, and benthic invertebrates, the highest bycatch risk was concentrated between 23°N and 25°N. For marine mammals and sea turtles, elevated risk was concentrated along China's southeastern coast, extending through inshore waters from the Yangtze River Estuary south to 20°N, with trawls and gillnets contributing most significantly to risk. Seabird bycatch hotspots were primarily located around islands, bays, and estuaries north of 20°N, where gillnets posed the greatest threat. Elasmobranchs experienced high bycatch risk from the Taiwan Strait to the Yangtze River Estuary and around Jeju Island, and were the most vulnerable taxa group overall. Bycatch risk for benthic invertebrates was largely restricted to narrow nearshore areas and was associated primarily with dredging activities. The study also found that marine protected areas generally exhibited lower bycatch risk than surrounding waters.