Most albacore catches from the Indian Ocean are by longline. While longlining is unlikely to have habitat impacts, it can have a bycatch of highly vulnerable species such as sharks, turtles, and seabirds.Around 90% of the albacore catch in the Indian Ocean is taken in pelagic and coastal longline fisheries. Most of the rest is by handlines and trolls, which are very selective and low-impact. A small amount of the catch is by gillnet, which would receive a default red rating from MCS owing to the very high levels of cetacean and turtle bycatch.A number of Endangered and Critically Endangered species are caught as bycatch in Indian Ocean longline fisheries, but scientifically recommended gear modifications to reduce impacts have not been implemented. Several countries have failed to implement national plans of action (NPOAs) for sharks, seabirds and turtles as required. Monitoring and reporting of bycatch in fisheries managed by IOTC is poor. Most data come from scientific observers on vessels. Scientific recommendations are that 20% of a fishery should be observed for accurate data. IOTC only requires coverage of 5%. Many fleets are not reaching this level. This makes it difficult to assess the impact of these fisheries on vulnerable species.Longlining for swordfish and albacore tuna takes place closer to the surface than in other fisheries. This increases the bycatch risk, as animals such as sharks and seabirds are more easily attracted to the bait.The IOTC reports that flatback, green, hawksbill, leatherback, loggerhead and olive ridley turtles are caught in its fisheries. Of these, hawksbills, southwest Indian Ocean leatherbacks, and northwest Indian Ocean loggerheads are critically endangered. Data on interactions is not regularly submitted, so the extent of bycatch is unknown. Gillnetting is the biggest concern for turtles, with estimates ranging from 11,000-52,000 individuals being caught annually. Longlining is estimated to catch around 3,500 turtles annually. In the southwest, longlining could be threatening local populations. Turtles can also be entangled by Fish Aggregating Devices used by purse seiners, and around 250 turtles are estimated to be caught by purse seiners annually. An estimated 75% of turtles are released alive from longliners and purse seiners. The scientific committee advises that maintaining or increasing fishing effort in the Indian Ocean without appropriate measures in place will likely result in further population declines. Current mitigation measures include requirements to release turtles wherever possible. Longliners must carry cutters or de-hookers to aid with this but scientifically recommended gear modification, such as circle hooks, is not required.Seabirds caught in IOTC fisheries include a number of endangered albatrosses, including the critically endangered Tristan albatross. Albatrosses and large petrels are amongst the most threatened groups of birds in the world, due in a large part to the impacts of bycatch in longline fisheries. Data on interactions is not regularly submitted, so the full extent of bycatch is unknown. Available information suggests higher sea bird bycatch at higher latitudes, and in coastal areas in the southern Indian Ocean. Impacts have been assessed in more detail in areas south of 25 degrees, and very high seabird bycatch rates have been recorded. This coincides with the greatest densities of albatrosses and large petrels. The scientific committee notes that the available evidence indicates considerable risk from longline fishing to the status of seabirds in the Indian Ocean. A recent assessment estimated that approximately 30,000-40,000 seabirds were killed by longlining in the Southern Hemisphere (including south Indian Ocean) between 2012 and 2016. The required longline mitigation measures, which only apply to areas south of 25 degrees S, do not follow recommended best practice. IOTC requires two measures from a set list of options, including weighted hooks, bird scaring lines and night setting. ACAP (the Agreement on the Conservation of Albatrosses and Petrels) recommends the simultaneous use of all three, or hook-shielding or underwater bait setting devices.Most bycatch of cetaceans is by gillnetting, but interactions with longliners have been recorded. Cetaceans such as pilot whales, Risso's dolphins and killer whales can be attracted by the fish caught on the line. These interactions are not well recorded and the scale of impact by longlining is unclear. There are no mitigation measures for longline. The IOTC scientific committee notes that maintaining or increasing fishing effort in the Indian Ocean without appropriate mitigation measures in place may result in further declines in a number of cetacean species.In 2020, around 82,000t of sharks were caught, with rays totalling around 1,800t. Gillnets are responsible for around 40% of the catch, followed by longline, handline, and trolling. It is estimated that around 30,000t is blue shark, which is not overfished or subject to overfishing. Most of the rest was not reported to species, so data on interactions is poor. However, species such as the critically endangered oceanic whitetip and scalloped hammerhead, and the endangered shortfin mako and pelagic thresher are known to be caught at significant levels in the Indian Ocean. The available evidence indicates considerable risk to these species. Mobulid rays are also bycaught and are declining across the Indian Ocean.There are some mitigation measures, such as restrictions on finning, and bans on retaining some species. Most thresher sharks die after being hooked, even if released. Therefore the ban on retaining them is probably not effective at protecting them. There are no gear-specific measures, in spite of evidence that this could reduce impacts. In the Atlantic, the use of circle hooks has been shown to increase survival of shortfin mako, blue marlin and swordfish if accidentally caught.
