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Tests were conducted aboard deep-set Hawaii (U.S.) tuna longline vessels to determine differences in catches, fish size selectivity and survival on 18/0 circle hooks vs. Japanese style tuna hooks size 3.6 sun and vs. 9/0 "J" hooks.  There were no significant differences in catch, catch rate or mean length between hook types for bigeye tuna (the primary target) but catch rates on circle hooks were lower for 16 other species than on the Japanese style tuna hook and for 8 species on the "J" hook.  Fish length was significantly shorter on Japanese style tuna hooks for four species compared to circle hooks and four 3 species on "J" hooks.  Survival was significantly higher for 6 species, including bigeye tuna, on circle hooks compared to Japanese style hooks and for five species on "J" hooks.

A software tool was developed to assess observer coverage with respect to several objectives for documenting or estimating rare-event bycatch. The ObsCovgTool predicts observer coverage performance for a given total fishery effort in relation to three metrics: (1) the conditional probability of observing any bycatch given that bycatch occurred in the fishery and the probability of any bycatch in the total fishery effort, (2) the upper confidence limit for total bycatch when none is observed, and (3) precision (coefficient of variation) of the bycatch estimate. 

Blue sharks (Prionace glauca) and oilfish (Ruvettus pretiosus) are frequently caught incidentally in the swordfish (Xiphias gladius) surface drifting longline fishery of the eastern Mediterranean Sea. An information theoretic generalized additive model approach, modelling separately: (1) the probability of making a catch; and (2) the positive catch rates, suggested the presence of intra-annual variations in their abundance and revealed interesting associations with some environmental features. Blue sharks were more frequently encountered during late summer in cool water masses. However, the likelihood of making a larger catch peaked in warmer waters through late spring in the vicinity of land. Occurrences of blue sharks were more frequent to the south-west (Ionian Sea), while positive catch rates were higher in the eastern-most regions (Levantine). Oilfish occurrences, as well as catch rates, were always above average to the east. Intra-annual variation was analogous to that of blue sharks. The species showed a preference for cooler water bodies and its distribution was strongly dictated by the lunar cycle. Annual time series showed a decreasing trend of blue sharks abundance. Catch rates for both species depended on fishing gear configuration. Deeper settings (.20 m), more resilient lines and use of fish attractant light-sticks increased the probability of capturing a fish.

A ten year study in the Aegean Sea, divided into two sub-periods (1995-2000; 2003-2006) examined bottom trawl fishery data for chondrichthyan fishes. A total of 30 different species were caught making up 14.3% of the total catch in weight and 2.2% by number. A significant decrease in the chondrichthan species richness  and abundance was observed. More than 90% (by number) of individuals were discarded at sea. 

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.

Penguins are one of the most threatened groups of seabirds, with 10 of the world’s 18 species listed as Vulnerable or Endangered on the IUCN Red List. At-sea threats, such as the bycatch of penguins in fishing gear has been the subject of few directed studies and has not been fully assessed. In this literature review, researchers assess which species and fishing gear are largest contributors to penguins globally. Authors suggest the accuracy of fully assessing penguin bycatch may be deceptive and quantitative estimates prove difficult as a lack of overall research, publishing bias, and random sampling in areas of perceived conflict or resource availability should be taken into consideration. 

Findings of this review identified 14 of the 18 total penguin species were recorded in bycatch events. Gillnets, and to a lesser extent trawls, were shown to pose the greatest threat to penguins. Of the 14 species, yellow-eyed Megadyptes antipodes (Endangered), Humboldt Spheniscus humboldti (Vulnerable) and Magellanic Spheniscus magellanicus penguins (Near Threatened) were the species of most concern in these bycatch events. Penguins face many threats; reducing bycatch mortality in fishing gear will greatly enhance the resilience of penguin populations to threats from habitat loss and climate change that are more difficult to address in the short term.

Harbor porpoise (Phocoena phocoena) avoided an area around a non-lethal, experimental gillnet equipped with a pinger in British Columbia, Canada. In a separate experiment with gillnets in the Baltic Sea, pingers did not affect the catch of targeted herring (Clupea harengus).

This study investigated the effect of acoustic pingers on the behavior of Burmeister's porpoise (Phocoena spinipinnis) in the vicinity of the Peruvian small-scale driftnet fleet. Over a 4-yr period (2009-2012), 116 control (without pingers) and 94 experimental (with pingers) fishing sets were observed, and porpoise acoustic activity around nets was recorded using passive acoustic loggers (C-PODs). In regions of preferred habitat associated with cooler (17-18 C), shallow waters (within the 100 m. isobath), the use of pingers lead to an 86% reduction in porpoise activity around nets. The results suggest that pingers are likely to be effective at deterring Burmeister's porpoises from fishing nets, and given the vast capacity of this and other fleets in the region, may substantially reduce mortality.

The use of blue-dyed squid bait on pelagic longlines was tested to determine its ability to reduce both surface and subsurface interactions with seabirds.  In addition, blue-dyed fish bait was tested for its ability to reduce seabird strikes at the surface. Blue-dyed squid bait reduced seabird interactions by 68% compared to non-dyed squid bait when the longline was submerged, and only 3-8% of the blue-dyed squid bait were struck at the surface, compared to 75-98% of non-dyed squid bait.  Around 48% of blue-dyed fish bait was struck at the surface during the first two days of the trial, and 90% were struck over the last three days of the trial.