Few appropriate management measures are in place for Indian Ocean yellowfin tuna. Stock rebuilding plans have been in place since 2016, but have been ineffective. Catches are too high, 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 yellowfin tuna is managed and assessed by the Indian Ocean Tuna Commission (IOTC). The stock is overfished and subject to overfishing. Interim rebuilding plans have been in place since 2016 to recover it to target levels. These have not succeeded.The rebuilding plans for 2016-2021 were based on reducing catches by 20% from 2014 levels (405,000t), with variations for different gear types. However, even with good compliance, the measures were actually estimated to achieve only a 10% reduction from 2014 levels. However, catches have increased. Provisional catch in 2020 was 432,624t, and the 2016-2020 average is 434,239t. It is projected that if catches are maintained at 2020 levels, there is a 76% probability that yellowfin biomass will remain below the target level and a 72% probability that fishing mortality will be above it by 2023, rising to 93% and 85% by 2030, respectively.Some countries, particularly the longline fleets, achieved the required decreases for 2016-2021, which is positive. The Maldives, which are economically dependent on healthy tuna stocks, decommissioned their longline yellowfin tuna fleet in 2019 (which was catching roughly 3,000 tons per year), to contribute rebuilding of yellowfin tuna. However, these efforts were offset by significant increases elsewhere, especially in the gillnet fleets. The plans to date have not, therefore, been adequately enforced, and management is inadequate to protect the stock.A number of concerns have been expressed relating to the rebuilding plans of 2016-2021. Catch reductions only applied to countries who caught more than 5,000t of yellowfin in 2014, so some countries may have inaccurately reported lower 2014 catches to escape the measures. Countries were allowed to determine their own methods for achieving reductions, resulting in inconsistent and ineffective approaches. The plans appear to have displaced activity onto purse seines using Fish Aggregating Devices (FADs), which has led to an increase in catches of skipjack tuna and juvenile yellowfin and bigeye.A new interim rebuilding plan for 2022 has included additional reductions and freezes on catch levels, which vary depending on catches for 2014/15 and 2017-2019. It is projected that the new measure will reduce catches to 401,000t if fully implemented, but it is too early to tell if it will be successful. A number of countries with high yellowfin catches objected to it, and therefore are exempt from the measure. While total catch reductions are crucial, specific focus is needed on reducing catches of juvenile yellowfin. There are no minimum size limits for this fishery to protect juveniles. Some gears, such as gillnets, FAD-associated purse seines, and poles and lines, catch high proportions of juveniles and may need further restrictions to protect the stock. It is also crucial to improve monitoring and compliance with management measures. Any rebuilding or management plan appears highly unlikely to succeed without significant changes to ensure that catch limits are being complied with.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 30% 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.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. In 2018 IOTC introduced a new measure 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, in 2021 the commission noted that data reporting issues persist. 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.It is possible that some catches are being misreported, as the boundary between the Atlantic Ocean and Indian Ocean stock is not clear. Genetic analysis suggests that much of the South African catch is from the Indian Ocean stock, while it is currently reported as Atlantic stock.Other IOTC conservation and management measures of note include:Discarding bigeye, yellowfin and skipjack tunas at sea is banned.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 will be 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.
