|Scope: Gulf of Mexico|
|Scientific Name:||Thunnus thynnus (Linnaeus, 1758)|
Scomber thynnus Linnaeus, 1758
Thunnus vulgaris Cuvier, 1832
Thynnus linnei Malm, 1877
Thynnus mediterraneus Risso, 1827
Thynnus secundodorsalis Storer, 1855
|Taxonomic Source(s):||Eschmeyer, W.N. (ed.). 2015. Catalog of Fishes. Updated 7 January 2015. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 7 January 2015).|
|Taxonomic Notes:||This is now considered to be a separate species from the Pacific bluefin, Thunnus orientalis (Collette 1999).|
|Red List Category & Criteria:||Endangered A2bd (Regional assessment) ver 3.1|
|Assessor(s):||Collette, B.B., Wells, D. & Abad-Uribarren, A.|
All known spawning of this species in the Western Atlantic occurs in the Gulf of Mexico. Based on the most recent 2014 ICCAT stock assessment, there has been an approximate 65% decline in SSB over the past 39 years (1972-2012), or three generation lengths in the Western Atlantic. Although the most recent stock assessment states that this species is either severely overfished, or not overfished depending on the recruitment mode, the ISSF considers that the western Atlantic bluefin stock is overfished with overfishing no longer occurring. This species is therefore listed as Endangered in the Gulf of Mexico under A2bd. Adjustments of quotas and new regulations to protect the spawning area have shown promise of increasing the size of the spawning stock biomass and modest increases in SSB are estimated to have occurred in the past few years in the Western Atlantic.
|Range Description:||This species' historical distribution was in the western Atlantic from Canada to Brazil, including throughout the Gulf of Mexico and the eastern portion of the Caribbean Sea (R. Robertson pers. comm. 2014). The bulk of the population off Brazil has now disappeared (Porch 2005, Takeuchi et al. 2009, Worm and Tittensor 2011). Over the last 20 to 36 years, the species has not been recorded off the coast of Brazil (Lessa and Amorim pers. comm. 2010) and there are no records of Bluefin Tuna in southern Brazil in the 21st century (Gasalla pers. comm. 2010).|
In the eastern Atlantic, it is present from Norway to the Canary Islands and as far south as Ascension Island (Wirtz et al. 2014). It is also reported from Mauritania (Maigret and Ly 1986) and off South Africa (Collette and Nauen 1983). It is present in the Mediterranean Sea and the southern Black Sea. Black Sea Bluefin Tuna was well documented in ancient times and there was an annual migration from the Black Sea to eastern Mediterranean spawning grounds. However, after World War II, the environmental condition in the Black Sea deteriorated and now sightings in the Black Sea are rare. An analysis of present over historical ranges concluded that Atlantic Bluefin Tuna has shown larger range contractions (minus 46% since 1960) than any other pelagic species (Worm and Tittensor 2011).
Native:Albania; Algeria; Anguilla; Antigua and Barbuda; Bahamas; Barbados; Belgium; Belize; Bermuda; Bonaire, Sint Eustatius and Saba; Brazil; Bulgaria; Canada; Cape Verde; Cayman Islands; Colombia; Croatia; Cuba; Curaçao; Cyprus; Denmark; Dominica; Dominican Republic; Egypt; Estonia; Finland; France; French Guiana; Germany; Gibraltar; Greece; Grenada; Guadeloupe; Guatemala; Guyana; Haiti; Honduras; Ireland; Israel; Italy; Jamaica; Latvia; Lebanon; Libya; Lithuania; Malta; Martinique; Mexico; Monaco; Montserrat; Morocco; Namibia; Netherlands; Nicaragua; Norway; Panama; Poland; Portugal; Puerto Rico; Saint Barthélemy; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Sint Maarten (Dutch part); Slovenia; South Africa; Spain; Suriname; Sweden; Syrian Arab Republic; Trinidad and Tobago; Tunisia; Turkey; Turks and Caicos Islands; United Kingdom; United States; Venezuela, Bolivarian Republic of; Virgin Islands, British; Virgin Islands, U.S.; Western Sahara
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Atlantic – northeast; Atlantic – eastern central; Mediterranean and Black Sea
|Population:||This species has become rare relative to historical levels because of massive overfishing (Fromentin and Powers 2005, Majkowski 2007, MacKenzie et al. 2009). The Center for Biological Diversity (CBD 2010) petitioned the U.S. Government to list the Atlantic Bluefin Tuna under the U.S. Endangered Species Act. The U.S. government agreed to conduct a status review for this species (Schwaab 2010), but decided not to list it as Endangered or Threatened but as a Species of Concern (NMFS 2011) with plans to review its status again in 2013.|
Genetic differentiation and homing to breeding sites indicates that there are at least three reproductively isolated stocks (Boustany et al. 2008, Carlsson et al. 2007) although there is considerable trans-Atlantic migration of individuals from the Mediterranean and western North Atlantic stocks (Rooker et al. 2008, Dickhut et al. 2009). The western Atlantic stock is found from Labrador and Newfoundland south into the Gulf of Mexico and Caribbean Sea; the eastern Atlantic stock from Norway south to the Canary Islands and the Mediterranean Sea. There is a distinct Mediterranean/East Atlantic stock but there is some mixing with the western Atlantic stock in the North Atlantic (Block et al. 2005); in addition, there are genetically recognizable populations within the Mediterranean (Riccione et al. 2010).
Worldwide reported landings show fluctuating, but relatively stable landings from 1950–1993, of between 15,000 and 39,000 tonnes per year. Reported catches increased to a peak of 52,785 tonnes in 1996, and then fell again to 38,830 tonnes in 2006 (FAO 2009). However, in many regions, the catch statistics for this species are considered to be unreliable because catches are not reported from some countries and landings data are confounded by ranching harvests occurring months to years after the fish have been caught (STEFC 2009). Based on the most recent stock assessment (ICCAT 2010), summed SBB biomass for both the Eastern and Western Atlantic stocks has declined at least 51% since 1970.
Western Atlantic Stock
In the western North Atlantic, the reported catch from 2000–2004 averaged 2,000–3,000 tonnes/year, and the status of the stock is Depleted (Majkowski 2007, ICCAT 2010). Western Atlantic Bluefin Tuna fisheries have been managed since the early 1980s (as of when 1982 quota restrictions were imposed) and catches have been relatively stable at around 2,500 tonnes (t) until 2001. They increased in 2002 to 3,319 t and have been declining since then, reaching 1,624 t in 2007. In 2008, catches increased again to 2,015 t. The most recent stock assessment (ICCAT 2010) is consistent with previous analyses in that spawning stock biomass (SSB) declined steadily between the early 1970s and early 1990s. Since then, SSB is estimated to have fluctuated between 21% and 28% of the 1970 level, but with a gradual increase in recent years from the low of 21% in 2003 to 29% in 2009. The stock has experienced different levels of fishing mortality over time, depending on the fish targeted by various fleets. A key factor in estimating MSY-related benchmarks is the highest level of recruitment that can be achieved in the long term. Assuming that average recruitment cannot reach the high levels from the early 1970s, recent F (2006–2008) is 70% of the MSY level and SSB2009 is about 10% higher than the MSY level. However, estimates of stock status are more pessimistic if a high recruitment scenario is considered (F/FMSY=1.9 and B/BMSY=0.15) (SCRS ICCAT 2010).
As linear regression did not provide the best fit for the steep declines observed in SSB over time in the Western Atlantic, using endpoints of the base case (ICCAT 2010) there has been an estimated 72% decline in SSB over the past 39 years (1970–2009), and a less than 1% decline in SSB over the past 21 years (1988–2009).
Based on the most recent stock assessment in 2012 (ICCAT 2014), there has been an approximate 65% decline in SSB over the past 39 years (1972-2012). Adjustments of quotas and new regulations to protect the spawning area have shown promise increasing the size of the spawning stock biomass, and modest increases in SSB are estimated to have occurred in the past few years (ICCAT 2014).
Based on the most recent stock assessment in 2012 (ICCAT 2014), the status of this species is either severely overfished, or not overfished depending on the recruitment model. For years, the SCRS has been unable to give an idea about which of the two assumptions is more plausible. ISSF considers that SCRS should revisit this issue as a matter of priority so that it can provide unambiguous advice that is based on one of the two assumptions. ISSF believes that it is more precautionary to assume that the high recruitment hypothesis applies and that the stock can be rebuilt to the higher levels estimated in the 1960s and 1970s. As a result, ISSF considers that the western Atlantic bluefin stock is overfished and that overfishing no longer occurring (ISSF 2014 Status of the Worlds Tuna Fisheries Report).
Gulf of Mexico (GOM)
The GOM is one of two major spawning grounds for Thunnus thynnus, the other being the Mediterranean. Although it is a large, migratory species all known spawning in the Western Atlantic occurs in the GOM from mid-April to June (Richards 1976, Stokebury et al. 2004). An index of abundance was constructed from logbook data in the US Pelagic longline fishery in the GOM for the time period 1987 - 2010. Thunnus thynnus is prohibited from being landed in the pelagic long-line fishery, which primarily targets swordfish, bigeye and yellowfin tunas, and is considered incidental bycatch in this fishery. This index was standardized for the use of weakhooks, which bend when a large fish in landed and result in a 46% reduction in the catch rates of T. thynnus. The percent decline in standardized CPUE from 1987-2013 (27 years) in the GOM ranged from 40-50% (Walter and Cass-Calay 2014).
Current climate forecasting models predict that water temperatures in the Gulf of Mexico (GOM) large marine ecosystem will be significantly affected by climate change (Christensen et al. 2007). Thunnus thynnus may be adversely affected by warm (>28-30 C) waters, and large individuals spawning in the GOM during the late spring may approach the limits of their cardiac capacity (Blank et al. 2004). A specific temperature window exists for spawning of T. thynnus in the GOM, therefore it is likely that shifts in water temperatures will affect the spatial and/or temporal distribution of spawning. Models predict that areas of larval occurrence will decrease in late spring by 39-61% by 2050 and by 93-96% by the end of the 21st century (Muhling et al. 2011). In Mexico, the catching season for this species is beginning earlier (moving from January in 1994 to November in 2007), with no change in fishing effort, which could be due to increasing water temperatures (Abad-Uribarren et al. 2014 Col. Vol. Sci. Pap. ICCAT 70(2) 684-698).
Eastern Atlantic and Mediterranean stock
In the Eastern Atlantic and Mediterranean stock, the reported catch from 2000–2004 averaged 32,000–35,000 tonnes/year, and the status of the stock is Over-Exploited (Majkowski 2007, ICCAT 2010). Currently this stock is fished at levels above FMSY, and estimated SSB is only about 35% of the biomass that is expected under a MSY (SRCS ICCAT 2010). The increase in mortality for large Bluefin Tuna is consistent with an apparent shift in targeting larger individuals destined for fattening and/or farming in the region. A quota system has been put in place to set levels for maximum sustainable yield (MSY) of 29,000 mt (STECF 2009), but current models put the MSY at 13,500 mt (SCRS ICCAT 2010). The current management structure has established TACs for the entire Mediterranean; however, recent genetic studies suggest multiple populations within the Mediterranean (Riccione et al. 2010). This is problematic because there is the potential for overfishing of segments of the Mediterranean population. In addition, information available has demonstrated that catches of Bluefin Tuna from the East Atlantic and Mediterranean were seriously under-reported between the mid-1990s through 2007. The lack of compliance with TAC and underreporting of the catch may have severely undermined the conservation of the stock (SRCS ICCAT 2010).
In the most recent stock assessment (SCRS ICCAT 2010), final estimated spawning biomass differs slightly between the two satisfactory model runs. The spawning biomass peaked at over 300,000 tonnes in the late 1950s and early 1970s, followed by a decline. Under run 13, the biomass continued to decline slightly to about 150,000 tonnes, while under run 15 biomass slightly increased during the late 2000s to about 2000,000 tonnes. Considering both runs, the analyses indicated that recent (2007–2009) SSB is about 57% of the highest estimated SSB levels (1957–1959).
Using endpoints of the base case (ICCAT 2010) there has been an estimated 45% decline in SSB over the past 39 years (1970–2009), and a 30% decline in SSB over the past 21 years (1988–2009) in the Eastern Atlantic stock.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||This is a pelagic, oceanodromous species, that seasonally can be found close to shore and can tolerate a wide range of temperatures. This species schools by size, sometimes together with Albacore, Yellowfin, Bigeye, Skipjack etc. It preys on small schooling fishes (anchovies, sauries, hakes) or on squids and red crabs. A recent study on the Mediterranean diet of this species provided evidence that juveniles prey mainly on zooplankton and small pelagic coastal fishes, sub-adults prey on medium pelagic fishes, shrimps and cephalopods, while adults prey mainly on cephalopods and larger fishes (Sarà and Sarà 2007).|
This species has a maximum size over 300 cm fork length (FL), but is more common to 200 cm. Longevity is at least 35 years and possibly to 50 years (Santamaria et al. 2009).
In the Western Atlantic, this species spawns in the Gulf of Mexico from mid-April to early June at temperatures of 22.6–27.5°C, starting at age 8–10 years at around 200 cm (FL), although most individuals first spawn closer to age 12 (Rooker et al. 2007, Rooker et al. 2008, Boustany et al. 2008, Diaz et al. 2009, Collette 2010). Recently, a few larvae were collected northeast of Campeche Bank suggesting that they were spawned outside of the Gulf of Mexico (Muhling et al. 2011). Maximum age is at least 32 years (Neilson and Compana 2008), although age composition structure has also changed over time (e.g., there are more younger individuals). For the most recent stock assessment, an age of first maturity was estimated to be approximately 145 kg or about age nine years in the Gulf of Mexico (SRCS ICCAT 2010). For the western Atlantic stock, the generation length is therefore estimated to be approximately 13 years based on average survivorship and fecundity across known scombrid stocks (Collette et al. 2011).
The Eastern Atlantic stock spawns in the Mediterranean Sea from May to August at temperatures of 22.5–25.5°C, starting at age three years and full recruitment is reached by age five years. There are distinct behaviours during the spawning time, most noticeably with changes in diving times and depths. Estimated relative batch fecundity is greater (more than 90 oocytes/g of body weight) than estimated for other tunas in the genus Thunnus (Sissenwine et al. 1998, Corriero et al. 2003, Rooker et al. 2007, Boustany et al. 2008, Rooker et al. 2008, Collette 2010). Fromentin and Powers (2005) reported that there is spawning site fidelity for this species both in the Mediterranean Sea and in the Gulf of Mexico. There are several spawning grounds throughout the Mediterranean. In addition, there are genetically recognizable populations within the Mediterranean (Riccioni et al. 2010).
Median sexual maturity in the Mediterranean Sea was reached at 103.6 cm (FL), and females weighing between 270 and 300 kg produce as many as 10 million eggs per spawning season (Corriero et al. 2005).
In the Eastern Atlantic stock and in the Mediterranean Sea, age of first maturity is about 3–5 years (115–121 cm FL), with a longevity of 35 years or more (Corriero et al. 2003, Santamaria et al. 2009, Rooker et al. 2007, Rooker et al. 2008). For the most recent stock assessment, an age of first maturity was estimated to be approximately 25 kg or age four years in the Mediterranean (SRCS ICCAT 2010). For the eastern Atlantic stock, the generation length is therefore estimated to be approximately seven years based on average survivorship and fecundity across known scombrid stocks (Collette et al. 2011).
Maximum Size (in cms) 458 (TL). The all-tackle angling record is of a 678.58 kg fish caught off Aulds Cove, Nova Scotia, Canada in 1979 (IGFA 2011.)
|Generation Length (years):||7-13|
|Movement patterns:||Full Migrant|
|Use and Trade:||This is a highly valued species for the Japanese sashimi markets, which has led to severe overfishing in both the Eastern and Western Atlantic. It is also an important gamefish particularly in the United States and Canada.|
This species is mainly caught by purse-seine, longline and traps. It is also used for commercial fish farming in the Mediterranean Sea.
The eastern Atlantic Bluefin Tuna stock is taken by a variety of vessels and types of fishing gears, with landing sites located in many countries. The main gears are longline, trap and baitboat for the east Atlantic, and purse-seine, longline and traps for the Mediterranean. Recreational fishing may also be a relevant but unquantified source of fishing mortality on juvenile Bluefin Tuna. The paucity of reliable data from various fisheries has compromised the stock assessments of the eastern Atlantic Bluefin Tuna stock for many years (see for example SCRS ICCAT 2010, STECF 2009). Size composition data from purse seine fisheries was missing for many years, particularly in the 1990s. For most of the 2000s, tuna farming compounded the problem of obtaining accurate catch and size-composition data because the fish cannot be accurately sampled until harvesting, which takes place from four months to several years after the fish are caught in the wild. The accuracy of overall catches has also been affected over time by under-reporting or over-reporting associated with quotas. In addition, data on juvenile Bluefin Tuna catches from the Mediterranean were also unavailable for many years. Since 2008, ICCAT has adopted several measures that should address these concerns, such as an increase in minimum size, and 100% observer coverage on purse seiners and transfers of fish to cages. However, despite the expectation that these measures will improve fishery statistics, substantial gaps remain in the historical data used for stock assessments.
In the western Atlantic, the fishery is conducted by the US, Canada and Japan. There are concerns over the potential impacts on the 2010 year class from the Deep Horizon oil spill that occurred in the Gulf of Mexico between April–August of that year (Campagna et al. 2011, Richards 2011).
Climate change is likely to impact migration, spawning and recruitment of Atlantic Tunas and billfishes, however potential responses and mechanisms remain largely unknown. Temperate species such as T. thynnus may be most vulnerable to the effects of climate change. Down-scaled climate variables were input into oceanographic habitat models in the Gulf of Mexico and indicated that climate change (warming) could substantially diminish potential spawning habitat of T. thynnus in the next 50 years (Muhling et al. 2014).
There are several conservation measures for this species mainly based on regulation of fisheries activities. The International Commission for the Conservation of the Atlantic Tuna (ICCAT) was established in 1967. Fisheries quotas have been set up since 1982, and a comprehensive pluri-annual recovery action plan adopted by the ICCAT contracting parties in 2007, including time closure for fishing activities and mandated reduction in fishing capacity. However, many conservation measures are not fully enforced and illegal catch continues. Enforcement of the existing measures is needed to prevent extinction of this species. Also, although the Bluefin Tuna probably has more data collected on it than most other fish species, uncertainties in the data make much of it unreliable. It is crucial to improve the quality of data if fisheries managers are going to be able to improve their methods.
High priority also needs to be given to protecting spawning adults in the Gulf of Mexico and Mediterranean Sea. Large adults in the northern foraging region in the Gulf of Maine and Gulf of St. Lawrence also need protection because this region represents critical refugia (Rooker et al. 2008). ICCAT has prohibited fishermen from targeting western Atlantic T. thynnus in their only known spawning ground, the Gulf of Mexico, however it is still taken as incidental catch in long-line fisheries targeting swordfish and sharks (ICCAT).
Eastern Atlantic and Mediterranean
For EU Member States, driftnet fishing for tuna has been banned since 1st January 2002, while the ban entered into force in 2004 for all the other Contracting Parties to ICCAT, as well as the GFCM Member States, but a driftnet fishing activity is still officially permitted in Morocco. The ICCAT further believes that a time area closure could greatly facilitate the implementation and the monitoring of rebuilding strategies. In 2006, ICCAT established a management plan to rebuild the stock to Bmsy by 2022 with 50% or greater probability (Rec. 06-05). As various issues related to implementation of the plan have come up, the plan has been amended and strengthened every year since. In [Rec. 09-06] the Commission established a total allowable catch for eastern Atlantic and Mediterranean Bluefin Tuna at 13,500 t for 2010. The current management plan (Rec. 10-04) calls for rebuilding to be achieved with at least 60% probability. It includes a number of conservation measures (country-specific TACs, minimum size limit, closed fishing seasons, management controls of fishing and farming capacity) as well as Monitoring, Control and Surveillance (MCS) measures (vessel registers, vessel monitoring systems, observer programs, transshipment prohibitions, weekly catch reporting, etc.). ICCAT has also approved a research program with different components aimed at improving data and knowledge of Bluefin Tuna biology and behaviour. It is still early to see what practical improvements these efforts will have on rebuilding the stock and improving stock assessments, but it is generally agreed that investments in research and MCS need to be sustained if overfishing is to be avoided.
Deferring effective management measures will likely result in even more stringent measures being necessary in the future to achieve the ICCAT objectives. STECF agrees with the ICCAT-SCRS that the minimum catch size should be set at 25 kg in order to avoid misreporting and/or discarded catches of mature fish between 25 kg and 30 kg. There remains an urgent need to have more reliable and complete size frequency data (particularly, but not only, for early year-classes 1–3) for the period following the introduction of a TAC in the Mediterranean. Tagging programs, fishery independent surveys and mining of historical data will all contribute to a better understanding of the status of this species and should be encouraged (STECF 2009).
In 1998, the Commission initiated a 20-year rebuilding plan designed to achieve BMSY with at least 50% probability. In response to recent assessments, in 2008 the Commission recommended a total allowable catch (TAC) of 1,900 t in 2009 and 1,800 t in 2010 [Rec. 08-04] (SRCS ICCAT 2010). Probabilities of achieving BMSY within the Commission rebuilding period were projected for alternative catch levels. The "low recruitment scenario" suggests that biomass is currently sufficient to produce MSY, whereas the "high recruitment scenario" suggests that BMSY has a very low probability of being achieved within the rebuilding period. Despite this large uncertainty about the long term future productivity of the stock, under either recruitment scenario current catches (1,800 t) should allow the biomass to continue to increase. Also, catches in the order of 2,500 t (the level established in previous TACs) would prevent the stock from rebuilding (SRCS ICCAT 2010).
As noted previously by the SCRS, both the productivity of western Atlantic Bluefin and western Atlantic Bluefin fisheries are linked to the eastern Atlantic and Mediterranean stock. Therefore, management actions taken in the eastern Atlantic and Mediterranean are likely to influence the recovery in the western Atlantic, because even small rates of mixing from East to West can have significant effects on the West due to the fact that Eastern plus Mediterranean resource is much larger than that of the West (SRCS ICCAT 2010, STECF 2009).
Directed longline fishing for bluefin in the Gulf of Mexico is prohibited, although a bycatch of one Bluefin Tuna is allowed during fishing directed at Yellowfin Tuna. Effective 5th May 2011, NMFS requires the use of “weak hooks” by pelagic longline vessels fishing in the Gulf of Mexico with the hopes that smaller Yellowfin Tuna will be retained on the hook and larger Bluefin Tuna will pull free (NMFS 2011). It is not yet clear if this technique will avoid adding to the thermal stress that longline-caught bluefins face on the spawning grounds in the Gulf of Mexico (Block et al. 2005).
It is strongly recommended that long-term larval studies in the Gulf of Mexico continue to assess the size of the population and to determine the potential impact of the Deepwater Horizon Oil Spill on the western Atlantic population, especially as the oil spill occurred during spawning season in May and June 2010. In addition, all tuna long-lining should be prohibited in the Gulf of Mexico during the spawning season in order to try to rebuild the population. There are closures of certain long-line fishing gear in April and May in the north central Gulf of Mexico, the primary area where this species spawns (Federal regulation in US). Incidental catch in the US Gulf of Mexico is allowed up to 100 tonnes per year catch, including dead discards.
|Citation:||Collette, B.B., Wells, D. & Abad-Uribarren, A. 2015. Thunnus thynnus. The IUCN Red List of Threatened Species 2015: e.T21860A76599358.Downloaded on 19 June 2018.|
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