Capture method — Troll
Capture area — Indian Ocean: Western (FAO 51), Eastern ( FAO 57)
Stock area — Indian Ocean
Stock detail — All Areas
Updated: November 2019
A stock assessment was carried out in 2018, indicating that the stock was overfished and subject to overfishing (spawning biomass, SB was estimated to be at 0.83 SB MSY and fishing mortality, F at 1.2 F MSY). There is some uncertainty in these estimates and a workplan is underway to address these uncertainties, although no new advice could be provided in 2019. Provisional catch in 2018 was 423,815 tonnes - an increase from 2017 (409,101t) and taking the 2014-2018 average catch to 404,655t. This is higher than the estimated Maximum Sustainable Yield, which is 403,000t. Projections indicated that if 2017 catch levels were to be maintained there would be a 100% probability of the stock exceeding its limits (SSB would be less than 0.4 SSBMSY and F would be above 1.4 FMSY) by 2027. Should catches increase by 10% to 450,000t, it is projected that the stock would crash by 2027. Reductions in catch of 20% or more (i.e. to around 327,000 t) would see the stock recovering to sustainable levels by 2027 with 50% probability. The stock status has been driven by unsustainable catches of yellowfin tuna taken over the last five years, and the relatively low recruitment levels in recent years. Some countries in the IOTC do not report fishery data which is important for stock assessment and management and in 2018, the IOTC introduced a new measure aimed at improving reporting on direct and incidental catches, including prohibiting a country from retaining a species if they fail to report catches for that species.
About 5% of the catch comes from troll fisheries. Trolling is a very selective method of fishing and typically uses less baitfish than pole & line.
Commercial buyers should establish what measures the flag state and fleet relating to their source is taking to improve reporting, local management and to recover the yellowfin stock. Some troll, handline and pole & line fleets here are in a Fishery Improvement Project making progress at improving elements of the fishery. More info about these FIPs is available from fisheryprogress.org.
Tuna belong to the family Scombridae. They are large, oceanic fish and are seasonally migratory, some making trans-oceanic journeys. Yellowfin are found throughout the world’s tropical and subtropical seas, except the Mediterranean. They often form large, size specific schools, frequently associated with dolphins or floating objects. Yellowfin is a large fast growing species, reaching maximum sizes of 240cm in length, 200kg in weight and an age of 8 years. They mature when 2 to 5 years old and mainly spawn in summer. Smaller fish are mainly limited to surface waters, while larger fish are found in surface and deeper waters, but rarely below 250m. Yellowfin has medium resilience to fishing.
Criterion score: 0.75 info
Indian Ocean stocks are managed by the Indian Ocean Tuna Commission (IOTC). Catches of Indian Ocean yellowfin tuna peaked in 2004 at over 500,000 t, dropped to around 250,000 t in 2009 and in recent years have stabilised at around 400,000 t. A stock assessment was carried out in 2018, indicating that the stock was overfished and subject to overfishing (spawning biomass, SB was estimated to be at 0.83 SB MSY and fishing mortality, F at 1.2 F MSY). Spawning stock biomass in 2017 was estimated to be 30% of the unfished levels. There is some uncertainty in these estimates and a workplan is underway to address these uncertainties, although no new advice could be provided in 2019.
Provisional catch in 2018 was 423,815 tonnes - an increase from 2017 (409,101t) and taking the 2014-2018 average catch to 404,655t. This is higher than the estimated Maximum Sustainable Yield, which is 403,000t. Projections indicated that if 2017 catch levels were to be maintained there would be a 100% probability of the stock exceeding its limits (SSB would be less than 0.4 SSBMSY and F would be above 1.4 FMSY) by 2027. Should catches increase by 10% to 450,000t, it is projected that the stock would crash by 2027. Reductions in catch of 20% or more (i.e. to around 327,000 t) would see the stock recovering to sustainable levels by 2027 with 50% probability.
The stock status has been driven by unsustainable catches of yellowfin tuna taken over the last five years, and the relatively low recruitment levels in recent years.
It is possible that the stock area does not match management areas, as the boundary between the Atlantic Ocean and Indian Ocean stock is not clear, but genetic analysis suggests that more of the South African catch is from the Indian Ocean stock, while it is currently reported as Atlantic stock.
Criterion score: 0.75 info
Most tuna stocks range across and are accessed by numerous coastal states, making harmonised and effective management of these individual stocks very difficult. To try and achieve this, Intergovernmental Regional Fisheries Management Organisations (RFMOs) have been established; for this stock it is the Indian Ocean Tuna Commission (IOTC). There are five main tuna RFMOs worldwide and it is their responsibility to carry out data collection, scientific monitoring and management of these fisheries. Whilst the RFMOs are responsible for the development of management and conservation measures, the degree to which they are implemented, monitored and enforced still varies significantly between coastal states. For this reason, it is important to choose tuna that has been caught by vessels that are well regulated by their flag state.
There are persistent failures by some countries to report to the commission annually, including reporting catch data, and other issues with lack of data and poor quality data persist. In 2018 IOTC introduced a new measure aimed at improving reporting on direct and incidental catches, including prohibiting a country from retaining a species if they fail to report catches for that species.
IOTC has set targets and thresholds for fishing effort and spawning stock biomass for the species it manages, but there is no Total Allowable Catch. The 2018 stock assessment indicates that the stock remains overfished and subject to overfishing, and that current catches remain unsustainable. There is a 100% probability of the stock falling below safe limits by 2027 if fishing pressure is not adequately reduced. In 2018 the scientific committee continued to recommend that catches should be reduced by 20% from to 2014 levels to around 330,000 tonnes. Provisional catch in 2018 was 423,815 tonnes, an increase of around 9% from 2014 levels. Work to implement a formal management procedure is underway, but not expected to be completed until 2021.
Widespread concern has been expressed about the state of the stock and lack of progress to rebuild it. Sainsbury’s, Waitrose, Marks and Spencer, Tesco, Asda, Morrison’s, Co-op, and New England Seafood International provided a joint statement to the IOTC in 2019 expressing their concern over the lack of an effective rebuilding plan and robust harvest strategy. The Maldives, which are heavily 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 Indian Ocean yellowfin tuna stocks.
A yellowfin tuna rebuilding plan has been in place since 2016, mainly focussed on reducing catches. In 2017, 2018 and 2019 the measures in force were estimated to achieve only a 10% reduction from 2014 levels. Some of the fisheries subject to catch reductions had fully achieved a decrease in catches in 2018 in accordance with the plan, but these reductions were offset by increases in catches from exempt countries. Some countries may have inaccurately reported their 2014 catches as being below certain thresholds so as to escape some measures.
The rebuilding plan requires countries whose 2014 catches exceeded certain thresholds (5000t for all gears except gillnet, which is 2000t) must reduce their catches by a certain amount compared to 2014 levels (purse seine by 15%, gillnet and longline by 10%, other gears by 5%). Countries can determine their own methods for achieving these reductions. If they exceed their catch limits, the excess is deducted from the following two years’ allowance. In addition, the number of supply vessels (which increase fishing capacity) is limited to 50% of the number of purse seine vessels in 2018-2019 and 40% in 2020-2022. The plan also ‘encourages’ countries to fast-track phasing out of gillnets, to set them at 2m deep to mitigate ecological impacts, and increase observer coverage on gillnetters to 10%.
Other IOTC conservation and management measures of note include:
A ban on the discarding of bigeye, yellowfin and skipjack tunas by purse seine vessels, as well as of non target species such as other tunas and billfish.
A ban on the use of aircrafts and unmanned aerial vehicles as fishing aids, which significantly contribute to fishing effort by helping to detect fish.
A ban on surface or submerged artificial lights for the purpose of aggregating tuna and tuna-like species beyond territorial waters.
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. within countries’ EEZs as well).
Regarding the use of drifting Fish Aggregation Devices (FADs): The maximum number of drifting FADs that can be in use at any one time by each purse seiner has been steadily reduced from 550 in 2015 to 300 in 2019, and the maximum that can be acquired each year reduced from 1100 in 2015, to 500 in 2019. 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 was a freeze on capacity and tonnage to 2006 levels for vessels over 24m, or vessels under this length operating in international waters. This measure expired in 2018, and IOTC reverted to previous legislation which froze capacity and tonnage to 2003 levels. 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.
5% regional observer coverage is required for all vessels over 24m and for vessels under 24m fishing outside of their Exclusive Economic Zone (EEZ). In 2019 a proposal was put forward to increase this to at last 20%, as 5% was considered to be insufficient. However, consensus on minimum coverage could not be reached.
To help address IUU, the IOTC maintains an active vessel register and an IUU Vessel List and prohibits transhipments for large scale vessels at sea unless they are pre-approved, monitored by an observer and the vessel uses a Vessel Monitoring System (VMS).
In 2016 IOTC introduced a number of resolutions to improve the poor compliance with existing management measures, e.g. observer coverage, catch and effort reporting, support for countries to implement measures.
Criterion score: 0 info
Trolling is a small scale method of fishing which uses lures or baited hooks attached to single lines which target tuna near the surface. It’s a labour intensive and very selective form of fishing and currently accounts for approximately 5% of the yellowfin catch in the Indian Ocean.
Based on method of production, fish type, and consumer rating: only fish rated 2 and below are included as an alternative in the list below. Click on a name to show the sustainable options available.Anchovy, anchovies
Herring or sild
Horse Mackerel, Scad
Salmon, Atlantic (Farmed)
Salmon, Chum, Keta, Calico or Dog salmon
Salmon, Pink, Spring , humpback
Salmon, Sockeye , Red Salmon, Bluebacks, Redfish
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