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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).

Four parts of the tori-pole were tested for their effectiveness in reducing the incidental catch of albatross in the Japanese southern bluefin tuna (Thunnus maccoyii) longline fishery.  Observer data were used to test: 1. bird line material, 2. streamer material, 3. bird line length and 4. pole height above sea surface.  The effectiveness of tori-poles in reducing albatross interactions increased with a longer bird line, but there was no difference in the effectiveness between the different bird line materials, type of streamer material or pole height above the sea surface.  

Several versions of a terrapin excluder design were tested on crab traps to determine how effective they were in reducing northern diamondback terrapin (Malaclemys terrapin)  bycatch, as well as the effect on catch rates of targeted blue crabs (Callinectes sapidus). All tests consisted of modified and unmodified traps being set in an alternate fashion. A wire bar placed across the opening of the traps was unsuccessful in reducing terrapin bycatch. A second design, which was a rectangular frame (5x10 cm) was successful. Standard traps caught 13 out of 15 terrapins during 1992 and 46 out of 51 during 1995, with the remainder of terrapins being caught by traps modified with the frame. Additional testing of the rectangular frame size, determined the 4.5x10 cm frame reduced terrapin bycatch the most (22 terrapins caught in unmodified vs. none in modified traps). Additionally, crab catch rates were 9% higher in the modified traps (4.5x10 cm) compared to the unmodified traps and crabs were of similar sizes in the two traps. In comparison, crab catch rates were 11% higher than in the unmodified traps when the 5x10 cm excluder design was used in 1994 (multiple sites) and 49% higher in 1995 (single site).

Interaction risk between the endangered Antipodean albatross (Diomedea antipodensis antipodensis) and fisheries was assessed by combining satellite-tracking data of individuals with data from AIS vessel tracking, as well as oceanographic data to determine how physical ocean features shape high-risk interaction zones. Hotspots for interactions ranged from 25°S to 40° S, varied seasonally, and were significantly higher in May-August and among juveniles. Interaction risk was also greatest where thermal fronts occur. Regional Fisheries Management Organizations could extend current bycatch mitigation measures to include fishing groups between 25 and 30°S to cover seasonal hotspots for juvenile and females. 

Small cetaceans are by-caught in salmon gillnet fisheries in British Columbia (BC) waters. In Canada, there is currently no generic calculation to identify when management action is necessary to reduce cetacean bycatch below sustainable limits. The researchers estimated potential anthropogenic mortality limits for harbour (Phocoena phocoena) and Dall’s (Phocoenoides dalli) porpoises and Pacific white-sided dolphins (Lagenorhynchus obliquidens) using quantitative objectives from two well-established frameworks for conservation and management (the United States’ Marine Mammal Protection Act and the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas), which are similar to some management objectives developed for marine mammal stocks elsewhere in Canada. Limits were calculated as functions of (i) a minimum abundance estimate (2004–2005); (ii) maximum rate of population increase; and (iii) uncertainty factors to account for bias in abundance estimates and uncertainty in mortality estimates. Best estimates of bycatch mortality in 2004 and 2005 exceeded only the most precautionary limits and only for porpoise species. Future research priority should be given to determining small cetacean stock structure in BC and refining species-specific entanglement rates in these and other fisheries. The approach offers a quantitative framework for Canada to meet its stated objectives to maintain favorable conservation status of cetacean populations.

Mobulid rays are distributed worldwide in tropical and warm temperate waters, and are landed as bycatch in many different fisheries. Five mobulid species (Mobula birostris, M. japanica, M.munkiana, M. tarapacana and M.thurstoni) are currently listed as vulnerable by the IUCN Red List for Threatened Animals for at least part of their geographic distribution. There is a lack of information on mobulid populations, and consequently it is very difficult to determine how the level of exploitation of mobulids in Indonesia may affected their stocks. Data in this study were derived from 409 mobulids that were taken as bycatch in drift gillnet fisheries targeting skipjack tuna (Katsuwonus pelamis), and subsequently examined at fish landing sites in Indonesia. Results identified M. japanica and M. tarapacana as the most abundant species represented. The disc width at maturity (DW50) of males, derived from the proportion of males at each size class with fully calcified claspers, ranged from 1538 mm for M. thurstoni to 3752 mm for M. birostris. The very low fecundity of the large and probably long-lived mobulid rays make the stocks of their species particularly susceptible to further increases in fishing.

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.

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.

Studies were conducted aboard beam trawlers in the North Sea to determine the performance of pulse beam compared to conventional tickler chain beam trawlers.  Overall the pulse beam trawl caught 68% less than the conventional trawls.  Specifically, the pulse beam trawl caught significantly fewer plaice (Pleuronectes platessa) and sole (Solea vulgaris) compared to the conventional beam trawl. There was no significant difference in catch rates of undersized plaice between the two gears but the pulse beam trawl caught significantly less undersized sole.  Pulse beam trawls caught more turbot (Psetta maxima) and brill (Scophthalmus rhombus) (78%-131%) than conventional trawls but fewer cod  (Gadus morhua) (15%-60%).  In addition, catch rates of bottom species, including sandstar (Astropecten irregularis), common starfish (Asterias rubens) and swimming crabs (Liocarcinus holsatus), were significantly less when the pulse beam trawl was used.

This study combines government reports, published journal articles, and data from a questinnaire administered to the fishing industry to assess marine mammal bycatch in Chile.