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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. 

Experiments were conducted aboard Korean pelagic longline vessels to determine if there were differences in the catch rates of target (tuna and billfish) and bycatch (sharks and other bony fish) species between 3 types of hooks; 4.0 traditional tuna hook (J-4), size 15 circle hook (C15) and size 18 circle hook (C18).  Within the target group significant differences between catch rates were only found between the J-4 and C18 hooks.  In the bycatch species group, significant differences were found between J4 and C15 and between J4 and C18.  Overall, the large circle hook (C18) had the lowest catch rates for tunas and other fish, while small circle hooks (C15) had the lowest catch rates for billfish and sharks.  Any differences in the length of fish caught by the individual hooks were minimal.

Tests were conducted on tuna longline fishing vessels in the eastern Pacific Ocean to determine if the use of J (size 4.0 traditional) or circle hooks (sizes 15, 16 and 18) and different bait resulted in differences in the catch rates of target and bycatch species. No significant differences in catch rates of the target species were found between hook types. Significant differences between J and circle hook size 15 and between J and circle hook size 16 were found in the bycatch species group (all species grouped together). The highest catch rates for tunas were found on circle hooks size 15 and for billfishes on J hooks. The largest circle hook (18) had the lowest catch rates. Squid and jack mackerel bait had the highest catch rates for tunas and other fishes, while chub mackerel bait caught the most billfish and sharks.

Tests were conducted on tuna longline fishing vessels in the eastern Pacific Ocean to determine if the use of J (size 4.0 traditional) or circle hooks (sizes 15, 16 and 18) and different bait resulted in differences in the catch rates of target and bycatch species. No significant differences in catch rates of the target species were found between hook types. Significant differences between J and circle hook size 15 and between J and circle hook size 16 were found in the bycatch species group (all species grouped together). The highest catch rates for tunas were found on circle hooks size 15 and for billfishes on J hooks. The largest circle hook (18) had the lowest catch rates. Squid and jack mackerel bait had the highest catch rates for tunas and other fishes, while chub mackerel bait caught the most billfish and sharks.

The study tested the vocalization response of harbor porpoises (Phocoena phocoena) to two different acoustic pingers, the AQUAmark 100 (20-160 kHz) and the AQUAmark 300 (10 kHz). Trials in Scotland and Denmark found that the AQUAmark 100 resulted in a significant reduction of porpoise vocalizations at 0,200, and 400 meters distance from the pingers. The vocalization behavior reveal no signs of habituation. Studies of the AQUAmark 300 resulted in a significant reduction of vocalizations at 0m and no significant reduction at 300m. Additionally, at one station, habituation effects were found.

The study evaluated the reactions of a six-year old harbor porpoise (Phocoena phocoena) to a banana pinger (Fishtek Marine Ltd.) in a controlled experiment at the SEAMARCO Research Institute in the Netherlands. The banana pinger sounds were comprised of signal blocks (duration ~0.5 s), each containing four frequency components (8–125 kHz; peak 70 kHz). Sounds were played back at mean received levels of 83, 89, 95, 101, and 107 dB re 1 μPa. Behavioral responses, including increased respiration rate, jumping, and swimming faster and farther away from the source, occurred from 95 dB re 1 μPa. At sea, distances at which harbor porpoises are deterred by pingers will depend on environmental parameters influencing sound propagation. 

A double-fish aggregating device (FAD) design was tested for its ability to mitigate the incidental capture of juvenile bigeye tuna (Thunnus obesus) in purse seine fisheries in the Western and Central Pacific Ocean. The design consisted of two separate FADs with underwater light stimuli attached. The number of animals caught was not large enough to conduct statistical analyses, but based on the weight of fish, the size proportion of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), and bigeye was bigger using the Double-FAD design compared to the standard design. The bycatch rate (proportion of total catch) of bigeye tuna was 6.1% and 7.2% using Double-FADs and 8.9% and 14.2% using standard FADs for numbers and weight respectively.  The proportion of skipjack tuna caught using the Double-FADs was 58.6% (number) and 29.1% (weight) compared to 72.4% (number) and 39% (weight) with the standard FAD.  The proportion of yellowfin tuna using the Double-FADs was 35.4% (number) and 63.7% (weight), while with the standard FAD, the proportion was 18.7% (number) and 46.8% (weight).  It appears this design has some effect on reducing bigeye tuna bycatch, despite the low sample size.

This study examined the spatial and temporal variations in bycatch rates of four species of great albatrosses (wandering albatross (Diomedea exulans), Tristan albatross (Diomedea dabbenena), southern royal albatross (Diomedea epomophora) and northern royal albatross (Diomedea sanfordi)). Observer data was obtained from the Uruguayan pelagic longline fleet and Japanese vessels operating in Uruguay. Vessel operational practices and habitat variables affected bycatch rates, including: setting time, moon phase, and area and season. 

A new toothless dredge design called the "Newhaven" was tested in the Isle of Man queen scallop (Aequipecten opercularis) fishery, to determine its effect on both catch and bycatch.  This new dredge design caught significantly more queen scallops compared to the traditional tooth dredge. However, there was no significant difference between the abundance of bycatch between the two dredge designs.  Bycatch species composition between the two dredge types was relatively similar but the "Newhaven" dredge did catch a significant number of dogfish (Scyliorhinus canicula).

Sea otters (Enhydra lutris) can be caught and drowned in fishing pots and traps. California sea otters were exposed to finfish traps, lobster traps, and mock Dungeness crab traps in captive trials.  Researchers found that the otters attempted to enter the circular and rectangular fyke openings and some became entrapped.  They determined that a 3x9 inch opening, rather than the standard 4x9 inch, would prevent bycatch of otters, while retaining crab catch.