Skipjack tuna

Skipjack tuna in the Indian Ocean is not overfished and not subject to overfishing.This stock is managed and assessed by the Indian Ocean Tuna Commission (IOTC). Indian Ocean skipjack has been caught since the 1950s. Catches peaked at over 600,000 tonnes in 2006, dropped to around 350,000 t in 2012 and in recent years have increased again to around 600,000t. The last stock assessment was carried out in 2023, using data up to 2022. The next stock assessment is expected in 2026.The dramatic fluctuations in catches correspond with significant drops in spawning biomass (SB). SB is estimated to have dropped from very high levels in the 1980s to below target levels (SB40%, 40% of unfished biomass) in the early 2010s. It has since recovered. In 2022, biomass was 53% of unfished levels and 230% of SBMSY. Therefore, the stock is not in an overfished state.The target for fishing mortality is the level consistent with keeping biomass at the target level (F40%SSB). F has continuously increased, but is below the target. In 2022, F was 55% of the target level and 48% of FMSY. Therefore, the stock is not subject to overfishing.There are no projections for how the stock will change in the coming years. However, catch in 2022 was 666,408t - the highest on record and substantially above the estimated Maximum Sustainable Yield of 584,774t as well as the catch limit of 513,572t. Scientists consider it likely that these recent catches have been sustained by favourable environmental conditions, but those conditions are predicted to become less favourable. It will be important therefore that future catches remain within the limits, and that environmental indicators are closely monitored to understand the potential impacts on the stock.

Few appropriate management measures are in place for Indian Ocean skipjack tuna. Recent catches have been well above catch limits, and monitoring and enforcement needs to be improved.Tuna, marlin, and swordfish are highly migratory species, found on the high seas and in numerous countries' waters. This makes harmonised and effective management challenging. Regional Fisheries Management Organisations (RFMOs) are responsible for monitoring and managing these stocks on behalf of the countries that access them. However, the degree to which management is implemented, monitored and enforced by each country varies significantly.Indian Ocean skipjack tuna is managed and assessed by the Indian Ocean Tuna Commission (IOTC). The main management measure is a Harvest Control Rule (HCR), which has been in place since 2017. It has a target of maintaining the stock at or above 40% of unfished levels. There is also a limit reference point, at which additional management measures would be expected, set at 20% of unfished levels. If the stock reaches 10% of unfished levels, fishing should cease. Catch limits are calculated using the HCR and data from stock assessments, carried out every 3 years. Management measures therefore appear to be based on scientific advice.However, management is very poorly monitored and enforced. Catch limits do not appear to be split between countries, so there is no agreement on how they should be allocated. The catch limit for 2021-2023 was 513,572 t. Catches substantially exceeded it, averaging 597,588t for those three years. The new limit for 2024-2026 is 628,605t. This is higher than the previous limit because the stock has remained productive thanks to favourable environmental conditions. However, those conditions are predicted to become less favourable. Catch in 2022 was 666,408t - the highest on record and well above the new catch limit.The scientific committee recommends that future catches remain within the limits, especially as fishing effort for skipjack may also have consequences for bigeye and yellowfin stocks, and that environmental indicators are closely monitored to understand the potential impacts on the stock.As well as catch limits, there are limits and reductions on the capacity of the fishing fleet. This mainly applies to the purse seine fleet, which accounts for around 50% of catches. The number of supply vessels, which increase fishing capacity of purse seiners, should be reduced. FADs, which attract tuna and increase catches, have also been reduced, from 550 per vessel in 2015 to 300 from 2019 onwards. Countries that use FADs must report regularly to the Commission and submit FAD management plans outlining how they will minimise mortality of juvenile yellowfin and bigeye tuna and vulnerable non-target species such as sharks, turtles and rays.As of January 2024, countries are encouraged to stop fishing for tropical tunas for a 31-day period (dates TBC), or implement voluntary catch reductions for yellowfin. These measures are not mandatory and therefore do not influence management scoring for this rating. There is a freeze on the capacity of the fishing fleet to 2003 levels, to prevent the fleet from growing. This legislation is very generic, applying across all fleets, and would be better replaced by spatial and temporal closures and quota allocation. There also appear to be concerns that the freeze has not been well enforced thus far.Monitoring and compliance with management measures in the IOTC region is generally poor. Some countries repeatedly fail to report catch data to the commission. Since 2018, IOTC has introduced several measures aimed at improving reporting on catch and bycatch, including prohibiting a country from retaining a species if they fail to report catches for it. However, the scientific committee continues to record issues with data reporting. Mandatory observer coverage is very low, at just 5% for all vessels over 24m or under 24m and fishing outside of their Exclusive Economic Zone (EEZ). A number of countries fail to meet the 5% threshold. In general, 20% is scientifically recommended to ensure adequate monitoring of catch and bycatch. In 2019 a proposal was put forward to increase coverage to at least 20%, but consensus could not be reached.Other IOTC conservation and management measures of note include:To help address Illegal, Unregulated, and Unreported fishing (IUU), the IOTC maintains an active vessel register and an IUU Vessel List. In 2021, all transhipments at sea were banned, except for large scale tuna longliners, which must be pre-approved, monitored by an observer and the vessel uses a Vessel Monitoring System (VMS).In 2012 IOTC banned the use of driftnets on the high seas. In 2022 this was extended to the entire IOTC area (i.e. including countries' EEZs).Using aircraft and unmanned aerial vehicles as fishing aids, which significantly contribute to fishing effort by helping to detect fish, is banned.Using artificial lights to attract tuna and tuna-like species beyond territorial waters is banned.

Some skipjack tuna from the Indian Ocean is caught by purse seining. This method is associated with bycatch of species such as sharks, rays, and turtles.Purse seining accounts for 54% of Indian Ocean skipjack tuna catches (around 340,000t in 2022). Most of these are from Fish Aggregating Devices (FADs) and the rest is on free schooling tuna, but it is not always possible to verify which catches are from which method.Purse seining is associated with bycatch of species such as sharks, turtles and marine mammals, although less so than longlining. Bycatch is higher when FADs are used. In the Indian Ocean, bycatch per ton of tuna averages 0.8% on free school sets and 3% on FADs. FADs are floating objects that tuna and other species tend to aggregate around. FADs can include hanging elements such as ropes and nets, which can entangle vulnerable species. FADs can also become lost at sea, continuing to ghost fish and be a source of marine debris.Some mitigation measures are in place. The IOTC is reducing the number of FADs that countries can use, and working on ways to reduce impacts through development of biodegradable and non-entangling FADs. Countries must submit FAD management plans outlining how they will minimise mortality of juvenile yellowfin and bigeye tuna and vulnerable non-target species such as sharks, turtles and rays.However, concerns remain. 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.Yellowfin tuna is often caught in purse seine sets targeting skipjack. The IOTC scientific committee has noted that the increasing proportion of juvenile yellowfin being caught, particularly in FAD skipjack fisheries, has reduced the maximum sustainable yield of the yellowfin stock. Yellowfin tuna is overfished and subject to overfishing.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.Most bycatch of cetaceans is by drift gillnetting. Purse seine nets have the potential to encircle or entangle the animals, although interactions are thought to be low. It is illegal to intentionally set a purse seine net around a cetacean. These interactions are not well recorded and the scale of impact of IOTC fisheries is unclear. In 2023, a new resolution was brought in requiring countries to report all cetacean interactions. The IOTC scientific committee notes that maintaining or increasing fishing effort in the Indian Ocean without appropriate mitigation measures in place will likely result in further declines in a number of cetacean species. In 2020, it was noted that there are tuna-dolphin associations for yellowfin tuna. The dolphins are not targeted, but can be caught as bycatch. This association appears to be widespread around the Indian Ocean, and is used by coastal country fishermen in Maldives, Sri Lanka, Oman and elsewhere to target yellowfin tuna.In 2021, around 80,000t of sharks and rays were caught. Longlines were responsible for around 40% of the catch, followed by gillnet (35%), and handline and trolling (15%). Much of the data is not reported to species levels, and data on sharks that are not retained is poor, so data on total interactions is poor. Purse seine is thought to account for less than 0.5% of total catches, but susceptible species include the endangered pelagic thresher, the longfin mako and the silky shark. 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.FADs are also of concern due to the unknown impacts such gear might have on other tuna and fish species in relation to species composition of schools, migratory patterns, growth rates and predation rates. Juvenile yellowfin and bigeye tuna are caught by purse seining, and scientific recommendations are for these impacts to be reduced to protect the stocks.