Longtail Tuna

FAO Species Fact Sheet
http://www.fao.org/fishery/species/2495/en

Scientific Name:
Thunnus tonggol

Authority:
Bleeker 1851

Common Name:
Longtail Tuna

LAUNCH GALLERY

Quick Facts

Longtail tuna, Thunnus tonggol, lives in the tropical and subtropical coastal waters of the Western Indian Ocean to the Western Pacific Ocean. It is not found in other oceans. Longtail tuna is found in water temperatures between 16℃ and 31℃. Juveniles and young adults prefer warmer waters and larger adults cooler waters. It lives in shallow waters less than 200 m depth and is most common at less than 50 m. It avoids water with low salinity and high turbidity. Unlike other Thunnus species, longtail tuna is not considered a highly migratory species.

TGG-003-FAO range map Thunnus tonggol
Large and continuing increases in landings throughout its range have motivated interest in the longtail tuna population stock structure and stock assessment for management. From several initial genetic studies, two stocks appear to occur: one along coastal northwest India and a separate, single stock across the South China Sea. Earlier genetic studies suggested a single stock along the coast of Australia and Papua New Guinea. Limited tagging data indicates some fish are capable of swimming hundreds of km in several weeks, yet most tagged longtail tuna maintain small ranges of only a few km over several years.

Longtail tuna is a small to medium-size tuna species, reaching maximum length of 136 cm fork length, maximum weight of 36 kg, and can live for at least 18 years, although most fish harvested are much younger. Longtail tuna in the northern hemisphere appear to grow faster than those in the southern hemisphere.. Longtail tuna feeds on marine crustaceans, fish, and cephalopods, and has a relatively slower growth rate than other tuna of comparable size.

FISHERIES

Historically longtail tuna has not been valued as highly as other tuna species such as the oceanic skipjack, yellowfin, bigeye, albacore and bluefin tuna. Despite currently supporting a large fishery, management agencies do not consider it a major commercial species. Because longtail tuna occurs in shallow coastal waters, it has local importance to smaller fishers for whom it provides income and food.

The Western and Central Pacific and Indian Ocean produce a total catch of approximately 250,000 tonnes per year. Between 1960 and 2014, reported landings have ballooned from 0 to 155,000 tonnes. In 2008, catches peaked at nearly 300,000 tonnes. The majority of reported longtail tuna landings (99%) are in the coastal waters of the following seven developing countries, namely (in order of 2015 landings), Iran, Indonesia, Pakistan, India, Oman, Malaysia, and Thailand.

Longtail tuna is primarily fished using gillnets, purse seines and troll lines. Gillnets target larger, sexually mature fish whereas purse seines capture smaller size classes, including juveniles. Although multiple gear types are used to target longtail tuna, gillnets are more commonly used in Pakistan, India, and Iran, purse seines used in Malaysia and Thailand, and trolls used in Indonesia, Yemen, and Oman, with gear type data incomplete for some countries. Free schools are targeted by the above gear. Juvenile longtail tuna may also be caught by fishers targeting other species associated with FADs.

SUSTAINABILITY AND MANAGEMENT

Recent assessments consider the Indian Ocean stock to be both overfished and subject to overfishing. However, there remains considerable uncertainty over the stock structure and total catches in the Indian Ocean. Research on longtail tuna in the Western Pacific Ocean is not as advanced and the number and status of stocks is unclear. No longtail tuna fishery has received certification of sustainability.

Management measures specific to longtail tuna fisheries are limited or absent. In the Indian Ocean, longtail tuna assessment and research is overseen by the Indian Ocean Tuna Commission. Coordinated monitoring of Western and Central Pacific longtail tuna is currently not in place. Longtail tuna stock assessments have and are being conducted in certain nation states, and efforts are underway, notably by SEAFDEC (Southeast Asian Fisheries Development Centre), to coordinate future research and management efforts for part of the range. Presently, longtail tuna is not covered in the mandate of the Western and Central Pacific Fisheries Commission.

The growth of fishing pressure on longtail tuna warrants research and management considerations, but existing tools that are effective for oceanic tuna fisheries may not be appropriate for neritic species like longtail tuna. Further, longtail tuna are less likely to receive international attention and management given that the species stays in near-shore, shallow water and avoids deeper, international waters. Since longtail tuna is commonly caught in multispecies fisheries, general fishing effort controls may be required to sustain longtail tuna across the Indo-West Pacific.

VALUE CHAINS

Longtail tuna is sold canned, smoked and fresh, including as sashimi, in domestic Indo-West Pacific markets and on the global market. Longtail tuna canning facilities are located in India, Indonesia, Iran, and Thailand and are supplied with fish captured primarily from purse seines. As a white meat tuna, canned longtail tuna is popular in markets such as in the Middle East, that sell other white meat species such as albacore tuna. In Indonesia, longtail tuna is cured by smoking and sold as a smoked fish. In Japan, longtail tuna is used fresh in sashimi.

FOOD

Information on the complete nutritional value of longtail tuna is not available. Comparisons among tuna indicate longtail tuna has lower fat and protein content than skipjack and yellowfin tuna.

ECOSYSTEM AND CLIMATE

Fishing affects attributed specifically to longtail tuna are difficult to assess because the species is commonly caught in multispecies fisheries, and landing reports across the Indo-West Pacific region are variable or incomplete. The carbon footprint of fishing for longtail tuna is likely small given fishing gear is primarily passive and deployed from small vessels with small engines and no refrigeration. In contrast, the ecological footprint of fishing longtail tuna is likely significant due to the use of large drifting gillnets that indiscriminately catch multiple tuna as well as species of conservation significance, including cetaceans and sea turtles. Ghost fishing by lost or damaged gillnets may also contribute to the unintended, yet significant loss of pelagic and benthic animals.

Longtail tuna catch processing likely creates a significant ecological impact. As for other fish species, canning and fresh fish processing use large volumes of water; large scale production and dumping of wastewater can contain high levels of organic, inorganic and particulate matter that pollutes local waterways.

Global climate change impacts on longtail tuna are not known, but from available biological and ecological knowledge, climate change is predicted to impact abundance and distribution through water temperature and prey changes. In decades to come, longtail tuna fisheries may become less productive in the tropics and grow in the subtropical and temperate regions.

Sustainability

WILD HARVEST FISHERIES

Throughout its distribution from the western Indian Ocean to the western Pacific Ocean, longtail tuna is a moderately common inshore species sought by both small scale fishers for local consumption and sale, and by commercial fishers for processing and export. It is vulnerable to many gear types, the most common of which are purse seines in various configurations, gillnets, longlines and trolls. Whilst some is caught in directed fisheries, more commonly longtail tuna is taken in fisheries that also target other neritic species such as bullet tunas, kawakawa, bonitos and seerfishes.

IUCN RED LIST STATUS

Unknown status, data deficient http://www.iucnredlist.org/details/170351/0.

The status is assigned because longtail tuna is longer lived relative to tuna species of similar size, its restricted distribution, the increasing catches and lack of fisheries data and stock assessments.

STATE OF THE STOCKS AND IMPACTS OF FISHING

In recent years, fishing on longtail tuna and other neritic tunas has increased. In the Indian Ocean, one stock of longtail tuna is assumed for stock assessments. The stock is assessed as being subject to overfishing and is overfished. Research on longtail tuna in the western Pacific is not as advanced and the number and status of stocks is unclear.

Indian Ocean

Stock Abundance

The most recent IOTC stock assessment assumes one stock for the Indian Ocean and suggests the biomass is in decline, subject to overfishing and is overfished state. The stock structure and the total catches are subject to considerable uncertainty (Indian Ocean Tuna Commission [IOTC], 2018).

Fishing Mortality

Catches have remained above MSY since 2011, except in 2015. Fishing mortality is currently estimated to be slightly below F_msy (IOTC, 2018).

Environment

No formal assessments of the impacts of the main fishing methods on the environment have been undertaken specifically for longtail tuna fisheries. About three quarters of the longtail tuna catch is taken in gillnets but this varies from country to country. Gillnets take large numbers of cetaceans in the northern Indian Ocean which is a source of conservation concern and probably having an adverse impact. Gillnets also take sharks but the range of species is unknown. Due to the inshore nature of the fisheries, the bycatch species will be different to those in offshore longtail tuna fisheries.

Longtail tuna taken in larger mesh purse seines (10 cm) has generally a small range of bycatch species and few juvenile fish. Purse seine fisheries in which longtail tuna are a bycatch take primarily juvenile fish. In Malaysia, longtail tuna is caught mainly on FADs and the catch is dominated by small fish.

Western Pacific Ocean

No coordinated assessment of the status of longtail tuna has been undertaken across its range in the western Pacific Ocean. However, several local assessments have been carried out.

Stock abundance

Over an 11 year period along western Peninsular Malaysia, no trend was observed in CPUE of longtail tuna and this was taken to suggest that fishing in this area was "sustainable."

In northern Australia, the stock is currently not considered to be experiencing growth overfishing (F current < F_MSY) or recruitment overfishing (F current < F_40%), but given the uncertainty in estimates of age at 50% maturity, the stock may be currently recruitment overfished if maturity is later than 2 years. The stock is above the established biological reference point (F_40%).

In Indonesia, using a surplus production model, an assessment concluded that the utilisation of neritic tunas (several species) in general was “moderate” and stocks were “healthy”; no specific conclusion was given for longtail tuna.

In Thai waters, neritic tunas are claimed not to be overfished for the period 2000-2011, although some contradictory evidence has also been noted.

Fishing Mortality

No stock based estimates of fishing mortality are available, although fishing mortality has been estimated directly from ageing data (2004-2006, Australia), and from modal progressions in length data (west coast peninsular Malaysia, Indonesia, Thailand).

Environment

Studies of bycatch of mammals and sea turtles commonly do not distinguish the fishing gear studied by key species of interest, e.g., a purse seine with a small mesh net used for small pelagics or larger nets used for tunas.

For Sarawak and Sabah (Malaysia), the incidental catch of cetaceans in purse seines (for which longtail tuna was recorded as catch but that were probably targeting small pelagics) was minor compared to the cetacean catch in gillnets (for which longtail tuna was not listed as a catch). In the Indian Ocean, longtail tuna once had been fished by pole and line when they associated with whale sharks but no substantiated records exist of whale sharks having been taken in these fisheries.

CERTIFICATES FOR SUSTAINABILITY OF WILD HARVEST FISHERY

No fisheries for longtail tuna have been certified.

FISHERIES ASSESSMENTS

T. tonggol is widely distributed in the coastal waters of the northern Indian Ocean and the western tropical Pacific Ocean (see Biology page) but limited evidence exists to support the case for a single or multiple stocks in each ocean. Some preliminary studies suggest that each ocean has one stock, but the areas sampled have not been comprehensive. This knowledge gap on stock structures has impeded accurate stock assessments.

INDIAN OCEAN

In the Indian Ocean, longtail tuna assessment is covered by the Indian Ocean Fisheries Commission (IOTC) and research and management advice is coordinated via the Commission’s Neritic Tuna Working Group. The Working Group takes information supplied by member countries (via fisheries agencies or research providers) and, where feasible, generates advice to the Commission about the need for, and potential format of, management measures.

Several stock assessments have been conducted, some being undertaken for fisheries in nation state waters or parts thereof. The outputs from these inform the ocean-wide assessment used as the basis for the IOTC’s judgement about overall stock status. Poor reporting by countries, coupled with a lack of information about the number of stocks increases the uncertainty about stock status.

WESTERN AND CENTRAL PACIFIC

Longtail tuna is not covered by the Western and Central Pacific Fisheries Commission (WCPFC) as it is not considered a highly migratory species. Up until June 2014 no regional coordination of research/management was provided for any of the neritic tunas but the finalisation of the SEAFDEC Regional Plan of Action (RPOA) for the Sustainable Utilisation of Neritic Tunas has provided a framework under which nations can collaborate. The RPOA is informed by four sub-regional working groups that cover the Sulu Sulawesi Sea, Andaman Sea, South China Sea and Gulf of Thailand.

FISHERIES MANAGEMENT

Although the total catch of longtail tuna in the Indo-Pacific region is comparable with that of bigeye and albacore tuna, it receives much less assessment and management attention due to the nature of its fisheries, and its coastal distribution that makes it less likely than the oceanic tunas to be subject to international management.

Based on area, gear type and season, longtail tuna may either be a low volume incidental catch (such as in the purse seine fisheries seeking small pelagics), a moderate volume catch (some gillnet fisheries where longtail tuna may be one of the dominant species taken) or the main catch (some gillnet fisheries and some purse seine fisheries where longtail tuna is clearly a target species). In Vietnam for example, longtail tuna is caught in both gillnets and purse seines but it is not a target species for either of these gear types; it is one of a suite of species of importance to fishers.

Unlike some of the oceanic tuna fisheries where effective, species-specific management measures are possible, the potential for sustainably managing longtail tuna via species specific measures seems limited. Nevertheless, management is required because longtail tuna is one of several neritic species that is experiencing strong and increasing fishing pressure. Input controls on fishing effort may be required to ensure that longtail tuna, and related species, are sustainably fished.

INDIAN OCEAN

In the Indian Ocean, longtail tuna is managed by member states of the Indian Ocean Tuna Commission (IOTC). No IOTC Conservation and Management Measures (CMM) are specific to longtail tuna.

In the Indian Ocean, longtail tuna is taken either in fisheries targeting neritic tunas (and tuna like species) or as a bycatch in fisheries targeting other pelagic species. The former include some purse seine and gillnet fisheries targeting larger fish whilst the latter include purse seine fisheries mainly aimed at small pelagics such as scads and mackerels.

In fisheries which are focused on catching neritic tunas, those for which the majority of the catch is longtail tuna (and thus could be called longtail tuna fisheries) are uncommon. Few, if any, fisheries have management measures aimed specifically at longtail tuna. Some fisheries have management measures aimed at the main species of interest and some fisheries may also have fisheries management measures that could have some incidental benefits for longtail tuna, such as seasonal closures on purse seining.

The management arrangements for 3 of the top 5 producers in the Indian Ocean are as follows:

Iran. Top two species are longtail tuna and kawakawa (Euthynnis affinis), managed by (a) for gillnets by size limits, mesh-size limits, engine power limits, time-area closures, licence, and (b) for troll line fishing, size limits, engine power limits, time-area closures, licence limitations.
Oman. Top two species are longtail tuna, followed by kawakawa (for artisanal gillnets), snappers and other benthic species (for artisanal troll and handlines); managed by gear type, vessel size and type, licences.
Pakistan. Gillnets, top two species longtail tuna and kawakawa, managed by vessel and fisher licencing.

WESTERN AND CENTRAL PACIFIC AND OTHER AREAS

The countries with fisheries for longtail tuna in the western Pacific Ocean do not have a coordinated approach to its management. Potentially, the RPOA for neritic tunas provides potential for coordination but this arrangement is at a very early stage.

Longtail tuna are usually taken in fisheries that are general pelagic species. The gillnet fisheries are focused on tunas and related species whereas most of the purse seine fisheries are focused on small pelagics.

The management arrangements for two of the top four producers in the Western and Central Pacific region are as follows.

Thailand (Gulf of Thailand). Main gear is purse seine, main species are longtail tuna and kawakawa (large mesh size), Indian mackerel spp and Indian scad spp (small mesh); managed by seasonal closures and, (a) for large mesh purse seine, closure season targeted towards small pelagics, and (b) for small mesh, minimum mesh size regulations.
Vietnam. Main gears are purse seine and gillnets, top two species are frigate tuna spp and kawakawa; no specific management arrangements for neritic tuna.

RECREATIONAL FISHING MANAGEMENT

In parts of its range, longtail tuna is a desirable species for recreational fishers due to its fighting behaviour as a sports fish and its good eating qualities.

In Australia, no commercial fishery is permitted to target longtail tuna. In Commonwealth managed tuna fisheries, a small bycatch limit is imposed. Longtail tuna catches by the recreational fishery are managed by State fisheries management authorities through daily catch and size limits.

AQUACULTURE

The aquaculture potential of longtail tuna has not investigated. However, researchers at Taiwan’s Fisheries Research Institute have successfully acclimated wild-caught longtail tuna in aquaria, indicating the species may be held in captivity for aquaculture purposes.

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GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For IUCN Red List, see Bruce Collette and colleagues (2011) and http://www.iucnredlist.org/details/170351/0.

For Indian Ocean stock status information, see the Indian Ocean Tuna Commission (IOTC) Stock Status Dashboard (http://www.iotc.org/science/status-summary-species-tuna-and-tuna-species-under-iotc-mandate-well-other-species-impacted-iotc), and Tom Nishida and K Iwasaki (2015), IOTC (2018), IOTC Secretariat (2015), Fatma Rashid Al-Kiyumi and colleagues (2014) (Oman), and Shane Griffiths (2010) (Australia) . For bycatch see R. Charles Anderson (2014), Richard Banks (2011) (Thailand), Pakjuta Khemakorn and Kingkan Vibunpant (2008) (Thailand), Pavarot Noranarttragoon and colleagues (2013) (Thailand), and Ahmad Adnan Nuruddin and colleagues (2015) (West Coast Peninsular Malaysia).

For Western Pacific Ocean stock status information, see Samsudin Basir and Sallehudin Jamon (2012) (West Coast Peninsular Malaysia), Shane Griffiths (2012) (Australia), T Hidayat and T Noegroho (2015) (Indonesia), P Nootmorn (SEAFDEC 2015) and P Nootmorn and P Khemakorn (2015) (Thailand). For environmental issues, see Saifullah Jaaman and colleagues (2009) (Sarawak and Sabah, Malaysia), and Mitsuo Yesaki (1987) for whale shark historical associations.

For longtail tuna stock structure as a basis for assessment, see Biology page, Fatma Rashid Al-Kiyumi and colleagues (2014), Swaraj Kunal and colleagues (2014) and Demian Willette and colleagues (2015). For assessment information in the Indian Ocean, see the IOTC Neritic Tuna Working Group (http://www.iotc.org/science/wp/working-party-neritic-tunas-wpnt); for information relevant to stock assessments in Southeast Asia, see SEAFDEC (2015).

For fisheries management information, see NV Nghia and P Hung in SEAFDEC (2015) (Vietnam), IOTC Neritic Tuna Working Group papers, and SEAFDEC (2015).

For recreational fishing information, see Shane Griffiths (2012).

REFERENCES

Al-Kiyumi, FR, L Al-kharusi, T Nishida & I Al-Anboori. 2014. Stock assessment of longtail tuna (Thunnus tonggol) in the NW Indian Ocean by ASPIC using standardized CPUE from drift gillnet fisheries in Sultanate of Oman, IOTC-2014-WPNT04-34.
Anderson, RC. 2014. Cetaceans and Tuna Fisheries in the Western and Central Indian Ocean. IPNLF Technical Report 2, International Pole and Line Foundation, London. 133 p.
Banks, R. 2011. Sustainability Assessment Report for Tonggol/longtail tuna (Thunnus tonggol) taken in the Gulf of Thailand and Andaman Sea, Poseidon Aquatic Resource Management Ltd, July 2011, 60 pp.
Basir, S & S Jamon. 2012. Catch performance of the purse seines for the neritic tuna fishing in the Strait of Malacca. IOTC-2012-WPNT02-20.
Collette, B, A Di Natale, W Fox, M Juan Jorda, N Miyabe, R Nelson, C Sun, & Y Uozumi. 2011. Thunnus tonggol (Longtail Tuna). The IUCN Red List of Threatened Species. Version 2015.2. . Downloaded on 27 July 2015.
Griffiths, SP. 2010. Stock assessment and efficacy of size limits on longtail tuna (Thunnus tonggol) caught in Australian waters. Fisheries Research 102:248–257.
Griffiths, SP. 2012. Stock assessment of longtail tuna in Australian waters: data input, model selection and assessing population status. IOTC-2012-WPNT02-2.
Hidayat, T. & T Noegroho. 2015. Neritic tuna fisheries in the South China Sea. Annex 8 in SEAFDEC. 2015. the First Meeting of the Scientific Working Group on Neritic Tuna Stock Assessment in the Southeast Asian Waters, Shah Alam, Selangor, Malaysia, 18-20 November 2014, Southeast Asian Fisheries Development Center. 95 pp.
IOTC (Indian Ocean Tuna Commission). 2018. Report of the Twenty-first Session of the IOTC Scientific Committee. IOTC: Seychelles, 3-7 December 2018. IOTC–2018–SC21–R[E], 250 p.
IOTC (Indian Ocean Tuna Commission) Secretariat. 2015. Assessment of Indian Ocean longtail tuna (Thunnus tonggol) using data poor catch-based methods IOTC, Seychelles.
Jaaman, SA, YU Lah-anyi, & GI Pierce. 2009. The magnitude and sustainability of marine mammal by-catch in fisheries in East Malaysia. Journal of the Marine Biological Association of the United Kingdom, 2009, 89(5), 907–920.
Khemakorn, P. & K Vibunpant. 2008. Purse Seine Fisheries in the Southern Gulf of Thailand Technical Paper No. 7/2008. Southern Marine Fisheries Research and Development Center (Songkhla) Marine Fisheries Research and Technological Development Institute, Marine Fisheries Research and Development Bureau, Department of Fisheries.
Kunal, SP, G Kumar, MR Menezes & RM Meena. 2014. Genetic homogeneity in longtail tuna Thunnus tonggol (Bleeker, 1851) from northwest coast of India inferred from direct sequencing analysis of mitochondrial DNA D-loop region. Marine Biology Research 10:738-743 DOI: 10.1080/17451000.2013.852682
Nghia, NV & P Hung. 2015. Country report neritic tunas in Vietnam. Annex 13 in SEAFDEC. 2015. the First Meeting of the Scientific Working Group on Neritic Tuna Stock Assessment in the Southeast Asian Waters, Shah Alam, Selangor, Malaysia, 18-20 November 2014, Southeast Asian Fisheries Development Center. 95 pp.
Nishida, T & K Iwasaki. 2015. Longtail tuna (Thunnus tonggol) stock assessment in the Indian Ocean by ASPIC (A Stock–Production model Incorporating Covariates) using available CPUE information. IOTC-2015-WPNT05-28 Rev_2.
Nootmorn, P & P Khemakorn. 2015. Neritic Tuna Fisheries in Thailand Annex 12 in in SEAFDEC. 2015. the First Meeting of the Scientific Working Group on Neritic Tuna Stock Assessment in the Southeast Asian Waters, Shah Alam, Selangor, Malaysia, 18-20 November 2014, Southeast Asian Fisheries Development Center. 95 pp.
Noranarttragoon, P, P Sinanan, N Boonjohn, P Khemakorn, & A Yakupitiyage. 2013. The FAD ﬁshery in the Gulf of Thailand: time for management measures Aquatic Living Resources. 26, 85-96.
Nuruddin, AA, S Jamon, EM Faizal, & S Basir. 2015. Neritic tuna fishery and some biological aspects in West Coast of Peninsular Malaysia. IOTC-2015-WPNT05-10.
SEAFDEC (Southeast Asian Fisheries Development Centre). 2015. the First Meeting of the Scientific Working Group on Neritic Tuna Stock Assessment in the Southeast Asian Waters, Shah Alam, Selangor, Malaysia, 18-20 November 2014, Southeast Asian Fisheries Development Center. 95 pp.
Willette DA, MD Santos & D Leadbitter. 2015. Longtail tuna Thunnus tonggol (Bleeker, 1851) shows an atypical partitioning into multiple stocks across the Indo-Pacific based on mitochondrial DNA. Journal of Applied Ichthyology, Accepted, in press. DOI 10.1007/s00338-015-1294-y.
Yesaki, M. 1987. Synopsis of biological data on longtail tuna, Thunnus tonggol. Indo-Pacific Tuna Development and Management Programme (IPTP), IPTP/87/WP/16, 56 p.

Production

SPECIES IMPORTANCE

As longtail tuna only occurs in the Indo-West Pacific region, all production is from this region. The total catch of longtail tuna is around 250,000 tonnes per year. This is similar to that of bigeye tuna in the Indo-West Pacific (264,000 t), slightly greater than that of albacore tuna in the Indo-West Pacific region (in 2014, about 212,000 t), much greater than that of southern bluefin tuna and northern Pacific bluefin tuna combined (29,000 t). Yet despite the size of the fishery, fisheries management agencies do not consider it to be a major commercial tuna.

The main catches are taken in the coastal waters of developing countries, particularly (in order of catch volume) Iran, Indonesia, Malaysia, Thailand, Oman, India, Pakistan and Yemen. In 2011, these eight countries accounted for 99% of reported landings. Reported landings have grown from zero to 155,000 tonnes over the period 1960 to 2014. Although a peak in landings of nearly 300,000 t was reported in 2008, the subsequent decline in reported landings may reflect changes in reporting (e.g. better identification) rather than any real decline.

The catch statistics contain considerable uncertainty. Many countries are considered to underreport longtail tuna, especially where the fisheries operate close inshore. This may, in part, be counterbalanced by some misidentification and some communication challenges. For example, in Indonesia longtail tuna is called "tongkol abu abu" but other neritic species also share the name "tongkol" and for many years the Indonesian government did not separate tongkols when reporting landings, resulting in significant over-reporting.

The importance of longtail tuna varies from area to area depending on catch volumes, importance relative to that of other species caught, and whether it has commercial value or is important for food security. As an inshore species it is accessible to more fishers than would be the case if it was more oceanic in habit and thus has local importance either as a food fish or as a source of income for smaller scale fishers. In some fisheries (also see Sustainability page) it can be a significant proportion of the catch (up to 70% for one of Thailand's purse seine fleets) and thus could be considered to be of major importance. Conversely, it is also commonly a very minor catch in fisheries directed at small pelagics (1%) and is thus of little or no importance.

FISHING METHODS

The gear types responsible for the majority of longtail tuna landings are gillnets, purses seines and troll lines.

Gillnets are designed to entangle fish that try to push through the meshes. They are the dominant gear used for longtail tuna in Iran, Pakistan and India. Whilst gill nets can be selective in terms of the size of the fish they catch (the larger the mesh, the larger the fish) they are less discriminating in terms of species caught and can also entangle species other than fish. Gillnets used to target larger size tunas can have mesh sizes of about 150 mm. Smaller mesh sizes are very common in the inshore fisheries and take smaller fish of a wide variety of species, including juvenile tunas.

Purse seine fishing nets with larger mesh sizes (100 mm or more) are used to target tunas whilst those with smaller mesh sizes (25-40 mm) are used to target small pelagics and those with even smaller mesh sizes (5 mm or less) are used for anchovies. Longtail tuna are vulnerable to both larger (100 mm) and smaller mesh sizes (25 -100 mm) with the smaller sizes generally being used in fisheries directed at small pelagics such as mackerels and scads. In fisheries for small pelagics, significant catches of juvenile longtail tuna are also taken, which reduces the stocks of adult longtail tuna and also may affect the status of the stock as a whole. In terms of purse seines, whilst the catch of juveniles in the small pelagic purse seines is small (generally <5%), the total weight of fish caught can be as large as the catch of adults.

The main sources of catches of troll caught fish are Indonesia, Yemen and Oman but information for this gear type is incomplete (but see links for Iran and Oman in the further reading section).

In addition, significant but inadequately recorded catches of longtail tuna are also taken in certain other fisheries, especially in the set net fisheries in Taiwan and Japan and the recreational fisheries in Australia and Oman.

The gear types used have differing impacts on age classes with gillnets generally taking the larger, sexually mature fish (75 cm in Iran, and purse seines the smaller fish (40 cm Thailand).

INDUSTRIAL-SCALE FISHERIES

Information on the destinations for catches from different gears is scarce. Canning facilities in the Middle East, India, Indonesia and Thailand are likely supplied by catches from gillnets and purse seines. Troll caught fish may or may not supply canning plants. In Thailand, domestically sourced longtail tuna for canning primarily come from the Thai tuna purse seine vessels (coded TUN in the Thai fisheries catch system).

In Iran, the larger gillnetters that carry freezing or refrigerated seawater facilities on board have about 10-15 crew. A small number of purse seiners carry a crew of about 30-35 along with another 10-15 crew used to man the dhow which takes out the net.

In Malaysia, the bulk of neritic tuna catches (dominated by longtail tuna and kawakawa, Euthynnus affinis) are caught by purse seine vessels of >70 GRT. Sets are made on both free schools and FADs and a wide variety of species is caught. The mesh size of the nets is not documented but when the catches (diversity of species) are compared to that of the Thai purse seine catches, the Malaysian fleet likely is fishing with smaller mesh nets so as to catch small pelagics as well as neritic tunas.

In Thailand, purse seine vessels are generally 24 m long and carry 35-45 crew. Fishing takes place in the early morning with vessels using sonar to locate schools of fish on the surface. The mesh size of the nets is about 100 mm which take fish close to the average size of first maturity.

In Pakistan, gillnet vessels are up to 23 m long and use nets up to 20 km long with an average 15 cm mesh size.

In India, about 81% of longtail tuna landings were taken by gillnet.

SMALL SCALE FISHERIES

As a coastal species, longtail tuna is more accessible to small scale fishers than many of the oceanic tuna species, especially in areas with a wide continental shelf.

As juveniles, longtail tuna are probably vulnerable to the widely used small mesh gillnets used by inshore fishers but the catches are probably very minor. In Thailand, the estimated catches by the small scale sector are very low in comparison to those from the larger scale vessels which catch 13,000 times the weight of the small scale catch.

In Oman and Iran, a variety of artisanal fishing vessels take longtail tuna. The vessels are generally small dhows and skiffs and the fishers use troll gear, handlines and gillnets.

In Indonesia, similar fishing vessel designs and fishing gear may be used by both small and larger scale fisheries and sometimes the distinctions by scale are difficult to make. The catches of longtail tuna are relatively large but so too is the number of vessels. Whilst much work has been undertaken to resolve catch reporting issues, much remains to be done to resolve catch by gear type and the markets for the catch.

RECREATIONAL FISHING

Recreational fishing is growing in countries like India but the recreational tourism companies do not specifically mention longtail tuna as a target species.

In Australia, no commercial fishery is permitted to target longtail tuna. Longtail tuna catches by recreational fishing are managed through daily catch number and size limits.

AQUACULTURE

Longtail tuna is not produced in aquaculture.

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GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For information on oceanic tuna catches, see ISSF (2015). For longtail tuna catches see FAO FishStatJ, and for specific information on Indian Ocean landings see IOTC (2015).

For gear types in the Indian Ocean, see IOTC (2015), and for FAD fishing in the Gulf of Thailand see Pacarot Noranarttragoon and colleagues (2013).

With respect to fishing gears that catch longtail tuna, the FAO FIRMS (Fisheries Resources Monitoring System) website provides useful information for several Asian countries. On the FIRMS search page (http://firms.fao.org/firms/fishery/search/en), find longtail tuna fishing gear information for a particular geographic area by entering “longtail tuna” and the area, e.g., country. At present, information is available for fisheries in Iran and Oman.

General descriptions of the main gear types used for the capture of longtail tuna can be found at:

Gillnets: http://www.fao.org/fishery/geartype/107/en

Troll lines: http://www.fao.org/fishery/geartype/235/en

Purse seines: http://www.fao.org/fishery/vesseltype/140/en

In addition to the above, for industrial scale fishing, see also Sallehudin Jamon (2014) (Malaysia); Praulai Chantawong (1999) (Thailand); David Ardill and colleagues (2013) and Muhammad Moazzam and Rab Nawaz (2014) (Pakistan); and EM Abdussamad and colleagues (2013) (India).

And for small scale fisheries, see D Lymer and colleagues (2008) (Thailand).

REFERENCES

Abdussamad, EM, KP Said Koya, P Rohith & S Kuriakaose. 2013. Neritic tuna fishery along the Indian coast and biology and population characteristics of longtail and frigate tuna. IOTC-2013-WPNT03-18.
Ardill, D, D Itano, & R Gillett. 2013. A review of bycatch and discard issues in Indian Ocean tuna fisheries. Indian Ocean Tuna Commission and Smart Fishing Initiative, Report No. SF/2013/32, 44 p.
Chantawong, P. 1999. Review on the status of small tunas along the Andaman Sea Coast of Thailand. IOTC Proceeding No. 2 (1999): 57-62.
IOTC (Indian Ocean Tuna Commission). 2015. Report of the 5th Session of the IOTC Working Party on Neritic Tunas. Zanzibar, Tanzania 26-29 May 2015. IOTC-2015-WPNT05-R[E], 105 pp.
ISSF (International Seafood Sustainability Foundation). 2015. ISSF Tuna Stock Status Update, 2015: Status of the world fisheries for tuna. ISSF Technical Report 2015-03A. International Seafood Sustainability Foundation, Washington, D.C., USA.
Jamon, S. 2014. Evaluating catches by FAD and free school purse seiners in the west coast of Malaysia. IOTC-2014-WPNT04-13, 8p.
Lymer, D, S Funge-Smith, P Khemakorn, S Naruepon, & S Ubolratana. 2008. A review and synthesis of capture fisheries data in Thailand large versus small-scale fisheries. RAP Publication 2008/17, FAO RAP, Bangkok, 2008.
Moazzam, M & R Nawaz. 2014. By-catch of tuna gillnet fisheries of Pakistan: A serious threat to non-target, endangered and threatened species. Ecosystem Approaches to the Management and Conservation of Fisheries and Marine Biodiversity in the Asia Region, 56(1):85-90.
Noranarttragoon, P, P Sinanan, N Boonjohn, P Khemakorn, & A Yakupitiyage. 2013. The FAD fishery in the Gulf of Thailand: time for management measures Aquatic Living Resources. 26, 85-96.

Supply Chains

POST HARVEST

Despite being less well known than some of the oceanic tunas such as skipjack and yellowfin tuna, longtail has a ready market in canned and fresh forms both in domestic and export markets. In addition to canning/fresh, longtail tuna is smoked, and used as sashimi.

CANNING

Longtail tuna is widely used in canned form. Markets include the USA, Australia, Finland and Sweden. Product forms include both consumer and catering pack sizes. Plants that can longtail tuna are located in India, Indonesia, Iran and Thailand.

In Thailand the fish destined to be canned for export are delivered to the cannery from purse seine vessels unloading fresh (unfrozen) at local ports (such as Songkla) or they are imported frozen. Once at the cannery the fish are graded for size and quality before being cooked. The meat is removed manually and placed in cans prior to vacuum sealing and labelling.

In Bitung, Indonesia, some longtail tuna is packed in catering-sized cans destined for the food service market in the USA. However, most is packed in consumer-sized cans under a variety of labels and sold to small retailers. Some of the larger tuna companies, which mainly focus on skipjack and yellowfin tuna, also carry a few Stock Keeping Units (SKUs) of longtail tuna as it is appreciated by those consumers that also like albacore tuna.

A number of companies based in India advertise the availability of canned longtail tuna but volumes and markets are unknown.

In some Middle Eastern countries longtail tuna is known as "tonggol" and is popular as a canned white meat tuna. In the United Arab Emirates, about 30% of the canned market is for white meat (albacore tuna and tonggol). Most of the white meat tuna consumed in Lebanon is tonggol.

SMOKED

In Indonesia, longtail tuna (known locally as tongkol abu abu) is hot smoked and is known as fufu/ikan asar, as is skipjack prepared in the same way.

SASHIMI

Longtail tuna is used for sashimi in Japan where it is known as koshinaga maguro. It is caught in Japan waters in the south west of the country. The use of longtail tuna in other sashimi markets is unknown.

COMMON MARKET NAMES

The FAO names are: longtail tuna (English), Thon mignon (French) and Atún tongol (Spanish).

Other names are: tongkol abu abu (Indonesia); koshinaga (Japan), and aya, kayu, tongkol hitam (Malaysia). In Malaysia and Indonesia, the name "tongkol" is used for several small tuna species from coastal waters, such as the mackerel tuna (Euthynnus affinis), longtail tuna (Thunnus tonggol), and frigate tuna (Auxis thazard).

In Australia, Thunnus tonggol is called longtail, tonggol, and, in the past, was called northern bluefin tuna.

NUTRITIONAL VALUE

Complete nutritional value information is not available for longtail tuna.

In Iran a study of fish from a processing factory compared a limited number of parameters (moisture, fat, protein, ash and Total Volatile Nitrogen content) for skipjack, yellowfin and longtail tunas and found that longtail had the lowest fat and protein content of the three species.

Little is known about the levels of mercury in longtail tuna, although it is often advertised as having a low mercury concentration. Studies in Malaysia and the Persian Gulf found similar ranges in the concentrations of total mercury of about 0.2 to 1.5 parts per million. Whilst the upper value was above the World Health Organisation recommended limit the average was below. In the Persian Gulf study the average was 0.4 parts per million.

Many vessels that do not have onboard refrigeration deliver their fish to market on ice, in brine, or salted. A small study in Iran found that current handling practices may pose health risks for human consumption of longtail tuna due to histamine-producing bacteria.

TRADE AND MARKETS

Longtail tuna is a valued catch where and whenever it is taken. Commonly, the neritic tunas, in general, and longtail tuna, in particular, are acknowledged as important in artisanal fishers. Despite this recognition, the trade in longtail tuna, is very difficult to understand accurately due to the lack of documentation of the inshore fisheries in which they are caught along with many other species.

Trade statistics do not specify longtail tuna. Listings for white meat tuna also include species such as albacore tuna. Thus, whilst canned longtail tuna has an export market, the volume traded and the full number of country markets is unknown. This lack of clear documentation is indicative also of traceability issues.

Consumer guides for longtail tuna, based largely on sustainability criteria, currently convey contradictions, likely reflecting the basic lack of information on the species and differences among the criteria used by different advisory agencies. Most of the consumer advice is provided by environmental non-government organisations. Typically, the advice is given for longtail tuna harvested in a particular country by a particular gear. Currently, the advice ranges from "avoid until more is known about the status of the stocks" to "avoid", and through to "green" or "good alternative." Some of the advice appears to have been predicated on conservation positions based on gear type, with little relevance as to whether longtail tuna is caught by the gear or even if the fishery is focused on neritic tunas.

EMPLOYMENT, SOCIAL FACTORS AND GENDER

No employment, social and gender-specific information could be found specific to the catches of longtail or neritic tuna species in general.

FISHING

Literature specific to labour and employment in fishing for neritic tunas is not available.

PROCESSING FACILITIES

In Indonesia and Thailand, longtail tuna is processed in plants that process other tuna species such as skipjack, albacore and yellowfin tuna (see Skipjack Tuna Supply Chains page). Processing plants are generally staffed by a majority of women on the processing floor. Some Thai plants are subject to social audits by purchasing companies based in Scandinavia and employment abuses such as have been uncovered in some other seafood processing facilities in that country are unlikely.

________________________

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For further information on nutritional value and quality, see Ali Aberoumad and Kiumars Purshafi (2010) (Iran). On mercury content, see P Hajeb and colleagues (2010) (Malaysia) and MS Mortazavi and S Sharifian, (2011) (Persian Gulf). On histamine, see Koohdar Valiollah and colleagues (2012).

For trade and markets, see various conservation NGO seafood consumer schemes.

For further information on tuna processing, see the Skipjack Tuna Supply Chains page).

REFERENCES

Aberoumad, A & K Pourshafi. 2010. Chemical and proximate composition properties of different fish species obtained from Iran. World Journal of Fisheries and Marine Science, 2:237-239.
Hajeb, P, S Jinap, & I Ahmad. 2010. Biomagnifications of mercury and methylmercury in tuna and mackerel. Environmental monitoring and assessment. 171:205-217.
Mortazavi, MS & S Sharifian. 2011. Mercury Bioaccumulation in Some Commercially Valuable Marine Organisms from Mosa Bay, Persian Gulf. Int. J. Environ. Res., 5(3):757-762.
Valiollah, K, R Vadood, K Abolhassan & S Alireza. 2012. Histamine-producing bacteria isolated from frozen longtail tuna (Thunnus tonggol). African Journal of Microbiology Research, 6: 751-756.

Environment & Climate

Longtail tuna is caught in multispecies tuna fisheries that may take a range of oceanic and neritic tunas and a range of bycatch species including pelagic sharks, billfish, seerfish, turtles and cetaceans. As such, attributing fishing effects on the environment and ecosystem specifically to fishing for longtail tuna is difficult. Furthermore, the quality and consistency of reporting of catch (including bycatch) and effort data in the many small coastal fisheries that operate in the countries that occupy most of the geographic range of longtail tuna has not allowed scientists to obtain a deep understanding of the impacts of longtail tuna fishing on the environment.

The primary means of catching longtail tuna is by passive fishing gears from small vessels (<15 m LOA) generally having no refrigeration. Thus, longtail tuna fisheries have a reasonably small carbon footprint. However, the extensive use of long (up to 20 km) drifting gillnets in countries such as Pakistan and India that indiscriminately catch a wide range of pelagic species, including species of conservation significance such as turtles and cetaceans, means some longtail tuna fisheries have a significant ecological footprint. In some countries, longtail is also commonly taken by trolling and seine nets (see Production).

Longtail tuna occupies a very narrow niche within the neritic pelagic zone. This habitat is likely to be impacted significantly under current ocean warming scenarios, possibly resulting in an expansion in the geographic range as longtail tuna moves to seek optimal thermal habitats. Many factors including spawning success and larvae survivorship as well as the responses of prey to climate change will dictate the long term sustainability of longtail tuna in the Indo-Pacific.

EFFECTS OF FISHING ON OTHER SPECIES

Along with many other species, longtail tuna is caught primarily with gillnets, purses seines, troll lines, ring seines and longlines, deployed by small scale and industrial scale vessels (see Production page). Significant catches of longtail tuna are also taken in other fisheries, especially in set net and recreational fisheries

Typically, the gears used to catch longtail tuna do not come into contact with the seafloor during normal operations and therefore do not affect benthic habitats or communities. However, ghost fishing from lost or damaged gillnets may be a significant source of mortality for pelagic animals, but also sessile epibenthos when the gear settles or moves across the seafloor.

Given the passive nature of gillnets, they are often unselective in terms of species caught, but highly selective for particular fish sizes, which is a function of the mesh size used, usually 110-165 mm when longtail tuna is caught. Most fisheries that capture longtail tuna are multispecies fisheries that target co-occurring species of small neritic tunas including kawakawa (Euthynnus affinis), frigate tuna (Auxis thazard), and bullet tuna (A. rochei), and seerfishers, including narrow-barred Spanish mackerel (Scomberomorous commerson). Gillnets can be up to 20 km in length in some countries such as Pakistan, and account for a range of bycatch species, many of conservation importance, including cetaceans, turtles, seabirds and sharks, including whale sharks. The numbers of animals captured as bycatch in these fisheries is not known accurately given the poor reporting systems in some countries and lack of scientific observer coverage. However, annual catches of cetaceans in Pakistan and Indian waters has been estimated to be 30,000 and 10,000 animals, respectively. In northern Australian waters where observer coverage of the drift gillnet fishery between 1979-1986 was high, around 14,000 cetaceans (mainly Tursiops truncatus and Stenella longirostris) were caught each year. In 1986, this marine mammal bycatch forced the closure of the fishery by the Australian government.

The set net fisheries in Taiwan and Japan, which account for a large percentage of the longtail tuna catch from these countries, are also multi species fisheries for highly diverse suites of commercially important pelagic fish such neritic tunas (E. affinis, A. thazard, A. rochei), dolphinfish (Corphaena hippurus) and billfish, notably sailfish. Set nets capture a large diversity of bycatch comprising pelagic and demersal species across a range of trophic levels including forage fishes, sunfish (Masturus lanceolatus), and sharks. Bycatch in these fisheries also includes five species of turtles and the whale shark, all listed by the International Union for the Conservation of Nature (IUCN), but these listed species are often released alive since nets are generally checked twice per day. In Taiwan, fishing for whale shark has been prohibited since 2008.

IMPACTS ON AIR AND WATER

Gillnet vessels that account for the majority of the global longtail tuna catch use fossil fuel to power both inboard and outboard engines, which produce greenhouse gases (GHG). GHG emissions are an exhaust byproduct from these engines that are the main contributor to global warming from the fishery. Although some vessels also produce GHG from refrigeration units, many vessels do not have onboard refrigeration and deliver fish to market on ice, in brine, or salted. Reliable estimates of the global carbon footprint of gillnet vessels are unavailable. The fleet of relatively small vessels, i.e., less than 20 m LOA, operating in the neritic regime catching longtail tuna using passive gear are most likely to consume a small fraction of the global industrial fishery GHG emissions (9 million metric tonnes in 2009). In 2010, the 20,000 gillnet vessels operating in Indian waters, but likely not all catching longtail tuna, produced 0.190 million tonnes of GHG emissions, which was 8% of the emissions from Indian trawl vessels. In 2012, Malaysian drift gillnet vessels produced 0.24 million tonnes of GHG emissions, which was 21% of the emissions produced by trawl vessels.

In 2010, the 20,000 gillnet vessels operating in Indian waters, but likely not all catching longtail tuna, produced 0.190 million tonnes of GHG emissions, which was 8% of the emissions from Indian trawl vessels. In 2012, Malaysian drift gillnet vessels produced 0.24 million tonnes of GHG emissions, which was 21% of the emissions produced by trawl vessels.

The most significant environmental impacts of the fisheries that catch longtail tuna is likely to be on water quality and subsequent ecological impacts as a result of catch processing. Large volumes of water are required for the processing of tuna for canning; for the fresh market, large volumes of water are used for washing and cleaning, and also for storage, refrigeration and as a transportation medium for fish between handling and processing phases. Wastewater, such as bloodwater, contains high concentrations of organic, inorganic and particulate matter that can have a negative effect on the environment. For example, discharge of suspended solids can reduce the biomass of aquatic macrophytes as a result of reducing the amount of light that can enter the water. Similarly, high concentrations of nitrates, phosphates and ammonia from high protein blood, oil and slime discharge can cause the eutrophication of local waterways. In many countries, stringent wastewater management regulations prevent pollution of the environment. However, the regulations in many countries that make the largest contributions to the global catch of longtail tuna are likely to be less stringent and enforced.

EFFECTS OF ENVIRONMENT ON LONGTAIL TUNA

The distribution of longtail tuna is governed by its physiological tolerance of maximum and minimum water temperatures of 16 ℃ to 31℃, respectively, and the presence of prey in sufficient quantities that can sustain its high metabolic rate, which is exacerbated by the lack of a swim bladder and high bioenergetic demands (see Biology). In most regions throughout its distribution, longtail tuna abundance is seasonal as the species in some cases appears to follows its preferred habitat envelope within seasonally moving water masses.

The vertical and horizontal distributions of tuna species common in the open ocean (e.g. yellowfin and bigeye tunas) are highly influenced by the depth of the thermocline and the minimum oxygen layer, which can vary with respect to El Niño/La Niña events in the Pacific Ocean. These oceanographic features can restrict their habitat, and at times make them more susceptible to capture by particular fisheries. In contrast, longtail tuna occupy relatively shallow waters that lack strong vertical temperature gradients and dissolved oxygen boundaries. Consequently, longtail are able to utilise the entire water column and are likely to have a relatively constant vulnerability to capture by fisheries.

Little is known about the effects of environmental regimes (e.g. El Niño/La Niña) on the relative distribution, abundance, and catchability of longtail tuna throughout its range. A small number of studies have analysed catch data with respect to physical oceanographic features such as temperature, but none have attempted to determine the long-term environmental drivers of longtail tuna productivity. However, anecdotal evidence from both commercial and recreational fishers on the east coast of Australia suggests that when rainfall is high during La Nina events longtail tuna distribution is patchy due to its avoidance of highly turbid lower salinity areas in the vicinity of large river mouths and it may even move further offshore into deeper waters.

EFFECTS OF CLIMATE CHANGE ON LONGTAIL TUNA

Under global climate change predictions by the Intergovernmental Panel on Climate Change (IPCC), the relative abundance of longtail tuna in specific areas may be expected to change in response to altered oceanographic regimes. However, given the uncertainty in global and regional climate forecasting, predicting climate impacts on longtail tuna is largely speculative. Longtail tuna occupies a narrow coastal habitat envelope that is predicted to experience the most rapid changes due to global warming. Increasing mean atmospheric temperatures will increase sea surface temperatures (SST), which will occur fastest in shallow coastal waters. This warming is predicted to increase the temperature and velocity of prominent ocean currents within the distribution of longtail tuna, such as the East Australia Current off Australia, the Kuroshio Current off the Philippines, Taiwan and Japan, the monsoonal currents within the South China Sea, and the Indian Ocean North Equatorial Current. This will extend the spatial extent of these currents, which may have several ecological and biological effects on longtail tuna.

The temperature preferences of longtail tuna means its distribution may be seasonally extended latitudinally, northward in the northern hemisphere and southward in the southern hemisphere as it occupies an expanding habitat. Surface waters may become too warm for longtail tuna near equatorial regions, resulting in a decrease in abundance and fishery catches in these regions as it moves poleward to seek more suitable habitat. Away from tropical regions, a subsequent possible increase in the abundance and the seasonal duration of longtail fisheries may allow the development of local fisheries, or force the movement of existing tropical fisheries.

Although the specific spawning locations of longtail tuna are poorly known, spawning probably occurs in tropical waters of 24-28℃ as for most tunas. Under climate warming, spawning may take place further poleward from existing spawning habitats. However, if suitable spawning habitats do not exist where SST is optimal for spawning, reduced recruitment success of larvae into the plankton and from the plankton to the adult population may result. This may potentially cause a decrease in the adult spawner biomass. Similarly, if longtail tuna continues to spawn in existing spawning locations, the elevated SST may decrease larval survival, potentially translating to a decrease in the adult population abundance.

The distribution and local abundances of longtail tuna may also be influenced by the presence of suitable prey in sufficient quantities that can satisfy its high daily prey consumption requirements. Elevated SST may cause a decline in the abundances of prey. Alternatively, longtail tuna may switch to more abundant prey that are tolerant of warmer waters, which may result in increased competition with other predators and a shift in the structure and trophic flows within ecosystems.

_________________________________________________________________

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For descriptions of fisheries for longtail tuna, see Production and Pillai and colleagues (2003); Shubhadeep Ghosh and colleagues (2010); Masahiko Mohri and colleagues (2010); Wei-Chuan Chiang and colleagues (2011) Shane Griffiths (2012); Shane Griffiths and colleagues (2013); Lucia Pierre and colleagues (2014).

For bycatch in longtail tuna gillnet fisheries, see Umair Shahid (2012); Ramūnas Žydelis and colleagues. (2013); Muhammad Moazzam and Rab Nawaz (2014). For indicative estimates of cetacean bycatch in gillnet fisheries, see Durant Hembree and Mary Harwood (1987); R. Charles Anderson (2014).

For bycatch in longtail tuna set net fisheries, see I. Jiunn Cheng and Tien-Hsi Chen (1997); Chuen-Chi Wu and colleagues (2001), Che-Tsung Chen and colleagues (2002); Wann-Duen Chiou and Liang-Kang Lee (2004); Hui-Xin Hong and colleagues (2004); Takeshi Yamane (2008); Wei-Chuan Chiang and colleagues (2009); Kwang-Ming Liu and colleagues (2009); Hua Hsun Hsu and colleagues (2012).

For on-water environmental impacts by the longtail tuna fishery (primarily drifting gillnet), see E Vivekanandan and colleagues (2013) and Nurashida Saad and colleagues (2014) for estimates of GHG emissions for India and Malaysia, respectively, and contrast to the global industrialised tuna fisheries described by Peter Tyedmers and Robert Parker (2012). For environmental effects of ghost fishing by gillnets, see Tatsuro Matsuoka and colleagues (2005).

For environmental impacts of tuna processing, see Kate Barclay (2010) and Pankaj Chowdhury and colleagues (2010).

For effects of the environment on longtail tuna through variability in preferred habitats, see Mitsuo Yesaki and Peerasak Jantarapagdee (1981); Masahiko Mohri and colleagues (2005); Masahiko Mohri and colleagues (2008); Shane Griffiths (2011); Masahiko Mohri and Yoritake (2014).

For effects of climate change on longtail tuna, see Terry Barker and colleagues (2007) for climate change scenarios and impacts on oceans and see Alistair Hobday and colleagues (2009) and Barbara Muhling and colleagues (2015) for modelling of closely related tuna species. For hypothesising plausible changes in spawning locations and larval survival based on closely related tuna species, see Kurt Schaefer (2001) and Jeanne Wexler and colleagues (2011).

For prey requirements of longtail tuna, see Shane Griffiths and colleagues (2007), while for environmental effects on prey species see Larry Jacobson and colleagues (2001).

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Chiang, WC, HH Hsu, SC Fu, SC Chen, CL Sun, WY Chen, DC Liu & WC Su. 2011. Reproductive biology of longtail tuna (Thunnus tonggol) from coastal waters off Taiwan, First meeting of the IOTC Working Party on Neritic Tunas, Chennai, India, 15 November, 2011. Document IOTC-2011-WPNT01-30.
Chiang, WC, CL Sun, SP Wang, SZ Yeh, Y Chen, WC Su, DC Liu & WY Chen. 2009. Analysis of sex-specific spawning biomass per recruit of the sailfish (Istiophorus platypterus) in the waters off eastern Taiwan. Fishery Bulletin: 265-277.
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Griffiths, SP, GC Fry, FJ Manson & RD Pillans. 2007. Feeding dynamics, consumption rates and daily ration of longtail tuna (Thunnus tonggol) in Australian waters, with emphasis on the consumption of commercially important prawns. Marine and Freshwater Research, 58: 376-397.
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Biology

DESCRIPTION

Longtail tuna is a small to medium size tuna with a robust anterior tapering to an elongated posterior, hence its common name of “longtail”. The first dorsal fin is similar to, or slightly smaller than, the second dorsal fin. The pectoral fins are long (22-31% of fork length) in fish Thunnus that lacks a swim bladder. The ventral surface of the liver lacks striations (as for yellowfin tuna, T. albacares) and the first gill arch has 19 to 27 rakers.

Body colouration ranges from black on the back to dark blue above the lateral line with an iridescent blue band extending along the lateral line from the top margin of the gills to the caudal keel. The flanks are silver, grading to a silvery-white belly with opaque horizontal rows of elongated oval spots, which are often absent in larger fish. The first dorsal fin ranges from dark blue to pale yellow, while the second dorsal and anal fins are silvery-white to pale yellow. The finlets are pale yellow with grey to black margins. The tail is black to dark blue, occasionally with a pale yellow colouration at the posterior base of the fork. The caudal keel is black to dark blue (as opposed to bright yellow in southern bluefin tuna, T. maccoyii).

ECOSYSTEM ROLE

In coastal ecosystems, longtail tuna plays an important role as both a predator and as prey, as it occupies different habitats as it grows. Juvenile and young adult longtail tuna (Euthynnus affinis) and frigate and bullet tunas (Auxis thazard and A. rochei) and, together, are prey for larger seerfish, billfish and sharks. Larger longtail tuna (>50 cm FL) occurs in smaller schools and as a solitary individual and is a near-apex predator consuming larger epipelagic fishes.

HABITAT AND DISTRIBUTION

Longtail tuna is distributed throughout subtropical and tropical waters from the Western Indian Ocean to the Western Pacific Ocean, between latitudes 47° N and 33° S. It extends from the sub-tropical east and west coasts of Australia, northward to southern Papua New Guinea and Indonesia and northwest through Malaysia and Thailand; it has a continuous distribution to the northeast to southern Japan and to the northwest through India, Sri Lanka, and Pakistan, to the Persian Gulf and the Red Sea. The species is nearly exclusively confined to the neritic regime within the continental shelves surrounding landmasses in waters of less than 200 m, but most commonly less than 50 m. This distribution differs from that of most other species in the genus Thunnus, which may move thousands of kilometres across ocean basins. In the neritic regime, longtail tuna is often absent near the mouths of large estuaries with low salinity and/or high turbidity. The absence of a swim bladder may be an evolutionary adaptation (or physiological constraint) for its apparent affinity for neritic waters and restriction to the surface mixed layers.

Analyses of data from electronic tagging of adult longtail tuna in Australian waters and fishery catches throughout the Indo West Pacific indicate it can tolerate water temperatures of between at least 17°C and 31°C. As juveniles to small adults, it tends to occupy more equatorial tropical waters and prefers water temperatures of 24-28°C, while larger fish appear to seasonally occupy cooler subtropical waters of 18-22°C. Although the species has been recorded to dive to 79 m, it has a strong affinity for the coastal regime and spends the majority of its time in waters less than 30 m. Longtail tuna does not appear to undertake distinct vertical migrations to surface at night, which is common in closely related species that occupy offshore waters, such as yellowfin and bigeye tunas.

Little research has been directed at defining the population stock structure of longtail tuna. Two studies using DNA genetic analyses in the northern hemisphere indicated that longtail tuna exist as a single stock throughout Indian waters and another within the South China Sea. Whether these two stocks are linked is unknown. In the southern hemisphere, analyses using early genetic techniques suggested the existence of a single stock throughout the waters of Australia and Papua New Guinea. Length frequency data from catches of longtail tuna made over many decades throughout the species’ distribution indicates a possible migration over its lifespan from equatorial nursery grounds to higher latitudes, and therefore a single stock. However, the existence of separate stocks of longtail tuna cannot be discounted considering the discontinuities and constrictions of neritic habitat and potential barriers presented by water masses throughout its global distribution.

Given the historic low commercial importance of longtail tuna in most countries, little tagging has been done. As a result, the movements of the species are poorly understood compared to those of closely related oceanic species. Evidence from limited scientific research and cooperative tagging programs with recreational fishers suggest that tagged longtail tuna at liberty for more than a few weeks are capable of travelling at least 650 km from their release points. Fish appear to move during the austral summer with seasonally expanding water masses, such as the East Australia current. Site fidelity is indicated from tagging in a few regions within the Indo-Pacific across a range of fish sizes, with many tagged fish being recaptured after several years within only a few kilometres of their release points. Whether fish move extensively and seasonally and visit preferred habitats such as large marine embayments or remain sedentary during the period at liberty is unknown.

GROWTH, REPRODUCTION AND DIET

Longtail tuna grows to a maximum weight of at least 35.9 kg, a total length of 136 cm FL, and age of at least 18 years. Despite the importance of longtail tuna to coastal commercial and subsistence fisheries in many countries, few biological studies have been undertaken, and the results of those obtained indicated that the reproductive and growth dynamics differ significantly between the northern and southern hemispheres.

In the northern hemisphere, longtail tuna reaches maturity at around 40-50 cm FL and spawns around the beginning and end of the monsoonal period between March-May and July–December. In contrast, longtail tuna in the southern hemisphere matures at 50-60 cm FL and has a single long spawning period that extends between October and April. In both hemispheres, longtail tuna produces between 768,000 and 1.9 million oocyctes per spawning, which may occur daily if water temperatures remain between 24–28°C, being the optimal spawning temperature for most Thunnus species. The sex ratio of fish in both regions is 1:1 males to females. In the southern hemisphere the sex ratio of fish >100 cm FL is closer to 2:1, but unfortunately no sex ratio data for large fish is available from the northern hemisphere.

The specific timing and location(s) of spawning by longtail tuna is poorly understood. However, based on catches of females in spawning condition and the presence of larvae, possible spawning areas in the northern hemisphere include the outer neritic zone in the Gulf of Thailand, the western Sea of Japan, and the East China Sea. In the southern hemisphere the evidence for spawning is less convincing, but may occur throughout the Gulf of Carpentaria, near Aru Islands in the Arafura Sea and deeper shelf waters near Broome, Western Australia.

Growth dynamics of longtail tuna in the northern hemisphere has been inferred in studies only by modal progressions in length-frequency data; these suggest the species is fast-growing but possibly variable, reaching 30-45 cm FL and 45-85 cm FL by year one and two, respectively. In Oceania, two growth studies separated by over 20 years using otoliths (ear bones) showed good agreement in suggesting that longtail tuna are slow-growing and reach about 100 cm FL by age five. In both hemispheres males and females did not differ in their growth dynamics.

Dietary studies undertaken in Papua New Guinea, Malaysia, Australia, and India show that longtail tuna is a highly opportunistic predator, primarily consuming epipelagic prey including schooling pelagic fishes (sardines, anchovies, scads, flyingfishes and needlefishes), squids, and crustaceans. However, at times its diet is comprised of a range of demersal and benthic prey, such as flatfishes, leatherjackets, stomatopods, crabs, and prawns, indicating fish may often forage close to the sea floor in shallow waters. The diet composition changes distinctly when fish reach about 100 cm FL, from consuming small schooling fishes and planktonic crustaceans to larger fish such as mackerels, scads, jacks, flyingfishes and needlefishes. Longtail tuna is a voracious predator that consumes an average of 2.36% of its body weight per day, although this consumption rate decreases during the spawning period. Longtail tuna primarily feeds during the daytime, but some feeding does occur during the night. Its importance as a high level predator may be most apparent in Australia where fish commonly exceed 100 cm FL and occupy a trophic level of 4.62.

GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For description of longtail tuna, see Bruce Collette (2001) and FishBase on longtail tuna, and on swim bladders, Jeffrey Graham and Kathryn Dickson (2001).

For ecosystem role, see AC Simpson and S Chikuni (1978); Mitsuo Yesaki (1982, 1987); Shane Griffiths and colleagues (2007a); Shane Griffiths and colleagues (2007b); Thomas Okey and colleagues (2007).

For global distribution, see Bruce Collette and Cornelia Nauen (1983); Bruce Collette (2001).

For stock distribution see Mark Wilson (1981); SZ Abdulhaleem (1989); Shane Griffiths (2010); Swaraj Kunal and colleagues. (2014); Demian Willette and colleagues (2015).

For feeding ecology see EG Silas (1967); Dominic Serventy (1942, 1956); Mark Wilson (1981); EM Abdussamad and colleagues (2012); Shane Griffiths and colleagues (2007a).

For movement and temperature preferences: Dominic Serventy (1956); Mark Wilson (1981); Mitsuo Yesaki and Peerasak Jantarapagdee (1981); Babera Kaltongga (1998); Masahiko Mohri and colleagues (2005); Masahiko Mohri and colleagues (2008); Shane Griffiths (2011); Masahiko Mohri and Kajikawa Yoritake (2014), and the NSW DPI gamefish tagging program (http://www.dpi.nsw.gov.au).

For size and age information in the northern hemisphere: Boonchai Chiampreecha (1978); Hiran Klinmuang (1978); EG Silas and colleagues (1986); Sakul Supongpan and Pairochana Saikliang (1987); Aghanashinikar Prabhakar and RG Dudley (1989); Mitsuo Yesaki (1989); Shubhadeep Ghosh and colleagues (2010); Farhad Kaymaram and colleagues (2011); EM Abdussamad and colleagues (2012); Dawood Al-Mamari and colleagues (2014), and for the southern hemisphere see Dominic Serventy (1942, 1956); Mark Wilson (1981); John Stevens and Stephanie Davenport (1991); Shane Griffiths and colleagues (2010a).

For reproduction and maturity, see: Mark Wilson (1981); Amara Cheunpan (1984); Shane Griffiths and colleagues (2010b); Wei-Chuan Chiang and coleagues (2011); Masoud Hedayatifard (2011); EM Abdussamad and colleagues (2012). For spawning see Mark Wilson (1981); Mitsuo Yesaki (1982); Yasuo Nishikawa and Shjoi Ueyanagi (1991); Tomoyuki Itoh et al. (1999); Paitoon Puewkhao and colleagues (2000); Shane Griffiths and colleagues (2010b).

For age and growth, see: Dominic Serventy (1956); Boonchai Chiampreecha (1978); Hiran Klinmuang (1978); Mark Wilson (1981); EG Silas and colleagues (1985); Sakul Supongpan and Pairochana Saikliang (1987); Aghanashinikar Prabhakar and RG Dudley (1989); Mitsuo Yesaki (1989); Shubhadeep Ghosh and colleagues (2010); Shane Griffiths and colleagues (2010a); Farhad Kaymaram and colleagues (2011); EM Abdussamad and colleagues (2012).

For diet and feeding see EG Silas (1967); Dominic Serventy (1942, 1956); Mark Wilson (1981); Shane Griffiths and colleagues (2007a); Masoud Hedayatifard (2011); EM Abdussamad and colleagues (2012).

REFERENCES

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Hedayatifard, M. 2011. The surveying of biological characteristics of long tail tuna (Thunnus tonggol) in the southern coasts of Iran, First meeting of the IOTC Working Party on Neritic Tunas, Chennai, India, 15 November, 2011. Document IOTC–2011–WPNT01–INF03.
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EXTERNAL LINKS

FAO Longtail Tuna Fact Sheet
http://www.fao.org/fishery/species/2495/en
IUCN Red List Longtail Tuna
http://www.iucnredlist.org/details/170351/0
IOTC Longtail Tuna Species Summary
http://www.iotc.org/science/status-summary-species-tuna-and-tuna-species-under-iotc-mandate-well-other-species-impacted-iotc
FishBase Longtail Tuna
http://www.fishbase.org/summary/148#
World Register of Marine Species (WoRMS)
http://www.marinespecies.org/aphia.php?p=taxdetails&id=219722
Encyclopedia of Life Longtail Tuna
http://eol.org/pages/212863/overview
Global Biodiversity Information Facility
http://www.gbif.org/species/2373933
CSIRO (Australia) Longtail Tuna
https://www.longtailtuna.com.au/

Contributors & Reviewers

Authors and Reviewers

Quick Facts: author Demian Willette; reviewers Duncan Leadbitter, Shane Griffiths; Updated Feb 2019 by Victoria Jollands
Sustainability: author Duncan Leadbitter; reviewers Ana Justel, Muhammad Moazzam Khan, Antony Lewis, Rishi Sharma, Shane Griffiths, Demian Willette; Updated Feb 2019 by Victoria Jollands
Production: author Duncan Leadbitter; reviewers Ana Justel, Antony Lewis, Shane Griffiths, Demian Willette
Supply Chains and Markets: author Duncan Leadbitter, reviewers Ana Justel, Antony Lewis, Demian Willette
Supply Chains and Markets - Indonesia (to be uploaded): author Thomas Nugroho
Environment and Climate: author Shane Griffiths; reviewers Ana Justel, Farhad Kaymaram, Antony Lewis, Prathibha Rohit, Duncan Leadbitter, Demian Willette
Biology: author Shane Griffiths, reviewers Ana Justel, Farhad Kaymaram, Antony Lewis, Prathibha Rohit, Demian Willette

Edited by Meryl Williams

Photographics and Graphics

United Nations Food and Agriculture Organization, Fisheries and Aquaculture Department (Thunnus tonggol image, distribution map)
Shane Griffiths - photographs
Antony D Lewis - photographs
Thomas Nugroho - photograph
Duncan Leadbitter - photographs

Information

The following agencies/people have provided additional resources, in addition to the references cited.

SEAFDEC (Southeast Asian Fisheries Development Centre), Somboon Siriraksophon

Funding and Support

Funding to prepare the longtail tuna profile was provided by the International Seafood Sustainability Foundation (iss-foundation.org) and the Asian Fisheries Society. Victor Restreppo, Chair of the ISSF Scientific Advisory Committee provided special support.
In-kind support has been provided by the host organizations of those who provided information and reviewed drafts.