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Observer data collected between 2011 and 2014 from the Fijian longline fleet was analyzed to characterize the shark and ray catch composition. In addition, factors that could significantly explain standardized catch rates were identified. Catch data were fitted to a generalized linear model to identify significant explanatory variables. The nominal catch rate for elasmobranchs was 0.610 per 1000 hooks. Twenty seven species of elasmobranchs were observed captured. Of the elasmobranchs captured, 48% are categorized as Threatened by the IUCN Red List. Sharks and rays made up 2.4% and 1.4% of the total catch respectively. The most commonly caught elasmobranchs were blue sharks ((Prionace glauca; 51% of sharks) and pelagic stingrays (Pteroplatytrygon violacea; 99% of rays caught). Significantly higher catch rates were observed on narrower J-shaped hooks compared to wide circle hooks. Catch rates of sharks and rays were lower during the latter half of the year. The fishery does not use 'shark lines'. 

Bycatch interactions with deep-sea elasmobranchs are increasingly common and can lead to dramatic declines in abundance over short time scales. Sharks hooked in the deep sea could face a higher likelihood of severe physiological disturbance, at-vessel mortality, and post-release mortality (PRM) than their shallower counterparts. Robust PRM rates have not yet been estimated for longline-caught deep-sea sharks, and as such are not currently incorporated into total fishery mortality estimates or bycatch assessments, limiting the effectiveness of current conservation or management initiatives. The researchers empirically estimated PRM for 2 focal taxa of deep-sea shark, the Cuban dogfish Squalus cubensis and the gulper shark Centrophorus sp., using post-release enclosures deployed at-depth. The researchers calculated 24 h PRM rates of 49.7 ± 8.5% (mean ± SE) for S. cubensis and 83 ± 16% for Centrophorus sp. and identified blood lactate, total length, glucose, and vitality scores as predictors of PRM in S. cubensis. The researchers also observed all 24 h PRM within 11 h post-capture and demonstrated the effects of recovery depth and at-vessel blood chemistry metrics on post-release behavior. The results suggest that PRM rates of deep-sea sharks are high and highlight the need for filling in this gap in fishery mortality estimates for other common discards in the future.

Fishery data collected from the Reunion Island and Seychelles pelagic longline fisheries (targeting swordfish and tuna) between 2004 and 2015 was used to propose depredation indicators and to assess depredation levels in these fisheries. The interaction rate (depredation) was significantly higher for sharks compared to toothed whales in both fisheries. However, there was a higher depredation per unit effort from toothed whales compared to sharks indicating the impact was more significant. The gross depredation rate in the Seychelles fishery was 18.3%. A slight increase in the gross depredation rate was seen over time in the Reunion Islands fishery (4.1% 2007-2010 and 4.4% in 2011-2015). These indicators were used to estimate the economic loss to these fisheries from depredation events. For the Reunion Island fishery the economic loss was 0.09 EUR/hook and 0.86 EUR/hook for the Seychelles. The results suggest a southward decreasing tooth whale and shark depredation gradient. The depredation levels in the Seychelles are some of the highest in the world and may suggest a 'hot spot' of interactions between toothed whales and pelagic longlines.

The study quantified the impact of turtle excluder devices (TEDs) on the catches of various elasmobranchs caught off northern Australia using data collected during a previous study (Brewer, et al., 2006). The effect of fish size and various aspects of TED design such as grid orientation, grid angle, and bar space were quantified to determine their effect on the escape of elasmobranchs from shrimp trawls. The relatively low number of elasmobranchs encountered during sampling resulted in a lack of power to isolate the effects of the various factors tested. Generally, the study showed that TEDs facilitated the escape of large elasmobranchs, including several species of conservation interest (the scalloped hammerhead, Sphyrna lewini and the zebra shark, Stegostoma fasciatum). Bar space and orientation were important TED design factors affecting the escape of elasmobranchs. Top-shooter TEDs enabled more Carcharhiniformes (“ground sharks”, including requiem sharks and hammerhead sharks) to escape penaeid trawls, while bottom-shooter TEDs increased the escape of Myliobatiformes (rays, including stingrays and cownose rays). However, the TED bar space that facilitates maximum escape of elasmobranchs while maintaining catch of the target species is more difficult to quantify given the low catch rate of elasmobranchs in the trawls. 

This study investigated bycatch events in the northern South China Sea through interviews of fishers. The majority of interviewed fishers reported an estimated 7,464 annual bycatch events, with sea turtles encountered most commonly followed by Indo-Pacific finless porpoises (Neophocaena phocaenoides), whale sharks (Rhincodon typus) and Indo-Pacific humpback dolphins (Sousa chinensis). The gear most associated with bycatch were gillnets, trawl nets, and seine nets. Modeling suggests that bycatch may be influenced by distance from the coast and water depth for marine mammals and sea turtles, but by administrative region for whale sharks.

The authors worked with creel fishers to trial and assess whether sinking rope was practical to fish with in Scottish inshore waters, and therefore to reduce entanglement risk  to minke whales (Balaenoptera acutorostrata), humpback whales (Megaptera novaeangliae), basking sharks (Cetorhinus maximus), and other megafauna. Overall, the fishers reported few problems with the modified gear, and the gear performed well underwater according to Remotely Operated Vehicle (ROV) footage and sensors. Sinking rope may be a simple, viable option to reduce entanglement risk in the Scottish creel fishery.

This study tested the use of an excluder grid with 90mm bar spacing to reduce bycatch of blackmouth catshark (Galeus melastomus) in  demersal trawl fisheries in the Mediterranean. The 90mm excluder grid was not very efficient in reducing blackmouth catshark bycatch because only the larger individuals were excluded, and the target catches of greater forkbeard fish (Phycis blennoides) and (to a lesser extent) Norwegian lobster (N. norvegicus) was reduced. Results of modeling suggest that reducing the grid bar spacing to 70mm would provide a better trade-off of reducing blackmouth catshark bycatch while keeping a high catch rate of greater forkbeard and Norwegian lobster.

The authors performed modeling on 10 years of logbook data to analyze environmental and operational factors that influence shark and odontocete depredation in the New Caledonian longline tuna fishery. Results suggest that there are "hotspots" of odontocete depredation, and that it is driven by environmental factors such as sea surface temperature and bathymetry, while shark depredation is driven by operational fisheries factors such as soaking time and number of hooks. Alterations such as reducing soaking time to under 12 hours, or setting limits on hooks to <1,750, could significantly reduce the likelihood of depredation. 

The authors analyzed data regarding the influences of environmental and spatial factors in shark bycatch in western and central Pacific longline fisheries from 2013-2021. Results suggest that several environmental factors, including oxygen concentration, sea surface temperature, and chlorophyll-a concentration, impact shark bycatch per unit effort (BPUE) for multiple shark species. Hotspots of bycatch were identified for bigeye thresher shark (Alopias superciliosus), longfin mako (Isurus paucus), silky shark (Carcharhinus falciformis), oceanic whitetip shark (Carcharhinus longimanus), blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus). All species exhibited annual variations in BPUE, and bycatch risk trended eastward toward equatorial waters, likely due to a higher concentration of fishing effort in those areas.

Large escape openings located at the sorting grid panel, which could be a beneficial tool to reduce marine megafauna bycatch, such as Greenland shark (Somniosus microcephalus), did not impact northern shrimp (Pandalus borealis) catch rates in comparison to traditional trawl gear.