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This study characterizes bycatch of marine mammals in fisheries that export fish to the United States of America from Ecuador, and identifies opportunities for collaboration on bycatch mitigation. The marine mammal species reported most frequently as bycatch were the humpback whale (Megaptera novaeangliae), bottlenose dolphin (Tursiops truncatus) and common dolphin (Delphinus delphis). Most interviewees indicated that the mammal bycatch rate has remained unchanged or increased over the last five years.

The effects of hook soak time on targeted reef fish and shark bycatch were investigated in the eastern Gulf of Mexico bottom longline fishery. Hook timers were used to evaluate capture time and catch per unit effort (CPUE) for the target species, red grouper (Epinephelus morio). The results indicate the typical duration of hook soak times is longer than needed to efficiently harvest red grouper. Reducing soak time to less than one hour would result in minimal to no reduction and CPUE of red grouper. Because the mean capture time of sharks and red grouper differ significantly, reducing the hook soak time would likely reduce bycatch of sharks in the fishery.

Study authors conducted a comprehensive review of technical bycatch mitigation measures for sharks for all major commercial fishing gears. Only one technique (changing fishing gear), received a “beneficial” Conservation Evidence (CE) rating (indicating a high level of certainty and effectiveness, and low probability of harm), demonstrating that no single bycatch reduction measure can be applied to all species, fishing gear, and regions. However, many different types of BRTs were rated as “likely to be beneficial”, although additional testing or information is needed. Furthermore, fishery-specific characteristics may mean that BRTs reported as effective in one area or fishery may not be as effective elsewhere. Even when a measure has been rated as being potentially beneficial, implementation in commercial fisheries may still not be feasible due to technical complexities, cost, safety issues, pollution issues, a negative impact on target catch (e.g., electropositive metals), or animal harm/welfare issues. Future research priorities should include development and incorporation of necromones (natural compounds released by decomposing organisms) into commercially viable artificial baits, production of active electrical repellents at scale to encourage uptake, investigating the impact of removal of light-sticks from longlines on shark catch rates, and refinement of circle hook design to reduce shark catch rates. 

Researchers tested modified hooks fitted with stiff wire appendages of different lengths (3.8 cm, 7.6 cm, and 11.4 cm) to determine whether they could reduce catch of yelloweye rockfish (Sebastes ruberrimus) in the Pacific halibut (Hippoglossus stenolepis) fishery on the west coast of the United States. The 3.8 cm and 7.6 cm appendage hooks reduced yelloweye rockfish catches by about 28% and 45%, respectively, while not significantly reducing Pacific halibut catches compared with standard hooks. Additionally, most fish were captured within the first two hours of gear deployment, so shorter soak times may improve fishing efficiency while reducing the potential for depredation and bycatch mortality. 

This report summarizes how seal scarers have been tested in Swedish waters, particularly in small-scale coastal fisheries. Results of the seal scarers have been mixed, with evidence of deterrence in trap fisheries, while in gillnet fisheries, there may be an attractive ("dinner bell") effect. Additionally, for small-scale coastal fishers, the use of seal scarers is unlikely to be commercially viable without financial incentives from government agencies. 

A monofilament gill net (267 mm stretched mesh, 10.5 meshes high, 10 mm braided float line with a foam core, twine diameter of 0.65 mm and a length of six nets at 120 m per net) was deployed in November 2019 at a depth of approximately 25 m off the coast of Cornwall (UK) during normal fishing operations. A single male bycaught porpoise (Phocoena phocoena) was recovered upon hauling the net. A multi-hydrophone passive acoustic monitoring system tracked the three-dimensional movements and acoustic behavior of the harbor porpoise, as well as a second animal that was in close proximity but did not interact with the net. The results indicated that the porpoises were foraging around the net prior to the bycatch event, that the bycaught animal lifted the net by approximately 7 m while entangled and that the two animals were potentially a social unit, with the surviving porpoise exhibiting unusual communication behavior for several hours after the bycatch occurred. Understanding behaviors prior to and during a bycatch event could significantly improve bycatch mitigation strategies in static net fisheries. 

Leaders in offshore, deep water pound nets in the Virginia portion of Chesapeake Bay (United States) incidentally take protected sea turtles. To reduce this take, federal resource managers restricted the use of traditional leaders during periods of peak sea turtle strandings. In response to these restrictions, a modified leader was developed. Testing of the new design in 2004 and 2005 indicated that the modified leader significantly reduced sea turtle interactions. Finfish were also sampled from the nets in the study, with results showing no difference in catch weights of four finfish species and the experimental leader harvesting significantly more of a fifth species than the control.

Average annual seabird bycatch in Alaska (U.S.) has declined by 73% in the last 5 years (2002-2006) compared to bycatch from the late 1990s. Despite the recent reductions resulting from mandatory mitigation requirements, seabirds continue to be caught at higher rates than would be expected, given results of controlled studies that demonstrated bycatch reductions of nearly 100% with paired streamer lines. The results of this study demonstrate that a few individual vessels continue to be responsible for the majority of seabird bycatch.

A questionaire administered to the bottom trawling fleet in the western Mediterranean (northeastern Spain) reported 238 bycacth events involving loggerhead sea turtles (Caretta caretta), calculated as a monthly CPUE of .09. The authors dicuss this figure relative to nearby coastal regions and suggest some possible mitigation measures.

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.