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Location | Gear | Catch | Technique | Bycatch Species | Type | |
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Seychelles and Reunion Island |
Hooks-and-Lines | Swordfish and tuna | Mammals, Sharks | Summary study | ||
Summary: Fishery data collected from the Reunion Island and Sechelles 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. Effect on Bycatch: N/A |
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Hooks-and-Lines | Sharks | Field study in the wild | ||||
Summary: 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. Unfortunately, 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. We 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. We 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. We 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. Our 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. Effect on Bycatch: |
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Northeast Atlantic Ocean |
Hooks-and-Lines | Tuna | Electromagnetic deterrents | Prionace glauca (Blue shark) | Field study in the wild | |
Summary: Two models of high field strength neodymium magnets (N35-Ni and N35-NdFeB types) were tested to determine their ability to deter sharks incidentally captured in Spanish and Portuguese longline fisheries operating in the Northeast Atlantic Ocean. The main shark species tested was blue shark (Prionace glauca). The larger magnet was 26 mm X 11 mm X 12 mm, 0.885 T and the smaller magnet was 20 mm X 13 mm X 15 mm, 0.464 t. Field test results indicated the magnets do not reduce blue shark catch rates and may instead have an attractive effect. The attractive effect was significantly higher for the larger magnets. Effect on Bycatch: Magnets did not deter blue sharks and may have had an attractive effect. |
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Seychelles |
Hooks-and-Lines | swordfish and tuna | Bony Fishes, Sharks | Summary study | ||
Summary: Experiments were conducted aboard longline vessels operating in the Seychelles targeting swordfish and tuna. Experimental longlines fitted with hook timers and temperature depth recorders were used to identify differences in species composition, quantity and depth of catch between night sets using a shallow basket (swordfish target) and day sets using both shallow and deep baskets (tuna target). The majority of species were caught during day sets (75%). Lancetfish was the main bycatch species during daytime sets. Sharks were the most common nightime bycatch species, with blue and shortfin mako sharks being the predominant shark species. All marketable species were caught in the 150 m layer, marlins were never caught below 100 m. Sharks were caught below 150 m during both night and day sets. For other bycatch species, all were caught in depths less than 150 m during night sets. Daytime depth captures varied. Effect on Bycatch: All marketable species were caught in the 150 m layer during day and night sets. |
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NE Atlantic |
Hooks-and-Lines | Tuna and blue sharks | Electromagnetic deterrents | Sharks | Field study in the wild | |
Summary: Pelagic longline hooks equipped with magnets were tested for their ability to repel blue sharks. Tests were conducted aboard pelagic longliners operating in the Northeast Atlantic Ocean. Two magnets, one large and one small, were tested. Magnets were manually attached to the hooks (polarized so the magnet field was oriented N or S and in parallel with the hook axis). Three test zones, each with 5 hooks with 1 magnet, 11 hooks with 2 magnets and 16 control hooks, were deployed along a longline. The results indicated that blue shark catch rates were not reduced with the use of magnets, and can instead have an increased attractive effect. The attraction was higher with the large magnet. Effect on Bycatch: Magnets increased and did not decrease blue shark catch rates. Larger magnets had a stronger effect. |
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Tyrrhenian Sea |
Trawls | Norway lobster (Nephrops norvegicus) and greater forkbeard (Phycis blennoides) | Excluder devices | Sharks | Field study in the wild | |
Summary: Trials were conducted using excluder grids on trawls targeting Norway lobster (Nephrops novegicus) and greater forkbeard (Phycis blennoides) in the Tyrrhenian Sea. The excluder grids were tested for their ability to reduce the incidental capture of blackmouth catshark (Galeus melastomus). In order to estimate the number of escaped fish, covers were placed over the escape outlet before the grid and over the codend. The 90 mm excluder grid did not result in reduced catches of blacknouth catshark. The grid did result in decreased catches of greater forkbeard and Norway lobster, to a smaller degree. Explorative simulations suggest a smaller grid spacing of 70 mm may prove more effective at reducing blackmouth catsharks catches. Effect on Bycatch: 90 mm excluder grid did not reduce catches of blackmouth catshark (Galeus melastomus) |
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Minch and Stanton Banks |
Trawls | Whitefish | Modified ground gear (mobile) | Sharks, Skates/Rays | Field study in the wild | |
Summary: A study was conducted to determine the impact of removing the 'tickler' from in front of groundgear of trawls. The 'tickler' is a length of chain placed in front of the groundgear of trawl gear, which is supposed to increase catches of sharks and rays. Tests were conducted where the 'tickler' was removed and secondary nets (groundgear bags) were placed behind the groundgear to determine the amount and species of fish that escaped capture. The results indicated that removing the 'tickler' from in front of the groundgear reduced the capture of skates and sharks. Therefore, prohibiting the use of 'tickler' chains in critical habitats for skates and sharks could be a beneficial management tool. Effect on Bycatch: Removing the 'tickler' chain resulted in decreased catches of sharks and skates |
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Massachusetts Bay |
Trawls | Silver hake | Excluder devices | Sharks | Field study in the wild | |
Summary: An excluder grate (grid) was tested in the silver hake trawl fishery in Massachusetts Bay to determine it's effectiveness in reducing spiny dogfish bycatch. The effects of color (white or black), angle and direction of the 50 mm spaced grids were investigated through video observations and data collection. The number of spiny dogfish caught in trawls with the excluder grate were greatly reduced for all gear configurations, while the number of target species caught remained within typical commercial quantities. Over 88% of spiny dogfish were excluded by the grate regardless of color or gear configuration. There were no observed differences in the behavior of spiny dogfish between gear configurations or grate colors. Effect on Bycatch: There were no observed differences in the behavior of spiny dogfish between gear configurations or grate colors. |
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Brazil |
Hooks-and-Lines | Tuna (pelagic) sharks (bottom) | Circle hooks | Sharks | Field study in the wild | |
Summary: The type (circle 18/0 0 degree offset and J-style 9/0 10 degree offset) and position of hooks in the water column were tested to determine the effects on catch rates and mortality of elasmobranchs. Tests were conducted aboard pelagic and bottom longline vessels. CPUEs for blue, silky and oceanic whitetip sharks were significantly higher with circle hooks than with J-style hooks. Silky, blue and oceanic whitetip sharks had a significantly higher mortality at haulback with J-style hooks. Significant differences in hooking location between the two hook types was found for night, blue, silky and oceanic whitetip sharks. These sharks were more commonly hooked externally vs internally. No significant differences between hook types was found for the CPUE's on bottom longlines. Significantly more blacknose were alive at haulback when circle hooks were used on bottom longlines. Bottom longlines were also used to test for differences in CPUE by fishing depth. Demersal hooks had significantly higher CPUE's than those suspended in the water column for blacknose and nurse sharks and southern stingrays. Effect on Bycatch: Mortality at haulback was significantly higher for on J-hooks. |
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Macduff Marine Aquarium, UK |
Non-specific | n/a | Electromagnetic deterrents | Sharks, Skates/Rays, Elasmobranchs | Study in the lab | |
Summary: Neodymium-iron-boron (Nd2Fe14B) permanent magnets were used to test behavioral responses in spotted catsharks (Scyliorhinus canicula) and thornback skates (Raja clavata). Both species significantly avoided the Nd2Fe14B magnets more often in comparison to the control and procedural control and they fed significantly more from the control an procedural control in comparison to the magnets. The study also demonstrated a correlation between avoidance speed and distance with water temperature. Effect on Bycatch: Species significantly avoided magnets |
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