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Summary: Magnets placed above hooks on longline gear created a strong magnetic field to reduce bycatch of nurse, lemon, and 4 additional shark species.

Summary:

To reduce turtle interactions, regulations for the Hawaii (U.S.)-based longline swordfish (Xiphias gladius) fishery required vessels to switch from using a J-shaped hook with squid bait to a wider circle-shaped hook with fish bait. Analyses of observer data showed that, following the introduction of the regulations, significant and large reductions in sea turtle and shark capture rates occurred without compromising target species catches. There was also a highly significant reduction in the proportion of turtles that swallowed hooks and a highly significant increase in the proportion of caught turtles that were released after removal of all terminal tackle. Research suggests that turtles aggregate at foraging grounds and that instituting methods to avoid real-time turtle bycatch hotspots may further reduce turtle interactions.

Summary: Longlines were set at depths greater than 100m using weighted lines to reduce bycatch of recreationally important fish species and protected species such as seabirds and sea turtles. While bigeye tuna catch rates were consistent between control and experimental sets, bycatch rates increased for sickle pomfret and opah but decreased for wahoo, dolphinfish, blue and striped marlin, and shortbill species. These species are generally not targeted but retained for their commercial value. Bycatch of sharks and pelagic stingrays did not differ between the experimental and control sets.

Summary:

A rare-earth metal alloy (cerium/lanthanide) was tested to determine if it could reduce bycatch of spiny dogfish (Squalus acanthias) in longlines and rod and reel fisheries in the Gulf of Maine, United States. Laboratory and field trials showed no significant reduction in dogfish catch.

Summary:

Rare earth metals (made of cerium mischmetal) were compared with control treatments of standard circle hooks and inert steel above circle hooks on longline fishing gear to determine if bycatch reduction of spiny dogfish (Squalus acanthias) could be achieved. Results indicated a slight reduction in dogfish bycatch and a greater reduction in catch of longnose skate (Caliraja rhina) on hooks with mischmetal. Problems for using mischmetal commercially include its expense, hazardous nature, and rapid hydrolysis in seawater.

Summary:

The potential of modifying gillnets to reduce shark bycatch was investigated in the US Spanish mackerel (Scomberomorus maculatus)  and spot (Leiostomus xanthurus) gillnet fisheries. The modified net had larger floats on the head-rope and increased weight on the lead-line to increase the tension of the net. Results showed that the catch rate of some shark species was significantly reduced in the modified gillnets. Target catch rates of Spanish mackerel did not differ significantly between control and modified nets of the same mesh size.

Summary:

In the eastern Pacific Ocean tuna fishery, a large fraction of non-mammal bycatch is captured by purse-seine gear when nets are deployed around floating objects. The researchers examined the spatial distribution of a dominant species in this fishery’s bycatch, the silky shark (Carcharhinus falciformis), from 1994 to 2005 to determine whether spatial closures might effectively reduce the bycatch of this species. The researchers identified candidate locations for fishery closures that specifically considered the trade-off between bycatch reduction and the loss of tuna catch and evaluated ancillary conservation benefits to less commonly captured taxa. Smoothed spatial distributions of silky shark bycatch did not indicate persistent small areas of especially high bycatch for any size class of shark over the 12-year period. Nevertheless, bycatch of small silky sharks (<90 cm total length) was consistently higher north of the equator during all years. The researchers evaluated nearly 100 candidate closure areas between 5◦N and 15◦ N that could have reduced, by as much as 33%, the total silky shark bycatch while compromising only 12% of the tuna catch. Closures also suggested reductions in the bycatch of other vulnerable taxa, including other shark species and turtles. 

Summary:

Catch rates of blue marlin (Makaira nigricans), snake mackerel (Gempylus serpens), and sharks were lower when nylon monofilament leaders, instead of wire leaders, were used on pelagic longline gear, but bigeye tuna (Thunnus obesus) and black marlin (Makaira indica) catch rates increased. There was no effect on yellowfin tuna (Thunnus albacares). Nylon leaders also had higher bite-off rates than the wire leaders.

Summary:

The use of circle hooks (4.3 sun and 5.2 sun) instead of standard Japanese tuna hooks (3.8 sun) in the pelagic longline fishery in the western North Pacific, had little impact on catch rates, mortality or size composition of blue sharks (Prionace glauca).

Summary: A semi-flexible exclusion grid with a bar spacing of 15.5 cm reduced dolphin bycatch in the Pilbara trawl fishery by close to 50% and reduced the bycatch of sea turtles, large sharks and rays. However, the fate of the dolphins that encountered the grid and escaped is unknown.