|Scientific Name:||Thunnus obesus|
|Species Authority:||(Lowe, 1839)|
Thunnus mebachi Kishinouye, 1915
Thynnus obesus Lowe, 1839
Thynnus sibi Temminck & Schlegel, 1844
|Red List Category & Criteria:||Vulnerable A2bd ver 3.1|
|Assessor/s:||Collette, B., Acero, A., Amorim, A.F., Boustany, A., Canales Ramirez, C., Cardenas, G., Carpenter, K.E., Chang, S.-K., Chiang, W., de Oliveira Leite Jr., N., Di Natale, A., Die, D., Fox, W., Fredou, F.L., Graves, J., Viera Hazin, F.H., Hinton, M., Juan Jorda, M., Minte Vera, C., Miyabe, N., Montano Cruz, R., Nelson, R., Oxenford, H., Restrepo, V., Schaefer, K., Schratwieser, J., Serra, R., Sun, C., Teixeira Lessa, R.P., Pires Ferreira Travassos, P.E., Uozumi, Y. & Yanez, E.|
|Reviewer/s:||Russell, B. & Polidoro, B.|
This species is important in commercial fisheries around the world. It is being effectively managed throughout the majority of its range, with the exception of the Western and Central Pacific stock. With the exception of the Western Pacific population, all other stocks are being fished below current maximum sustainable yield (MSY). Based on weighted declines of total biomass or spawning stock biomass (SSB) across all stocks, there has been an estimated 42% decline globally over the past 15 years (1992–2007), or three generation lengths. As the MSY of the Western and Central Pacific stock represents more than 20% of the global population, this species is listed as Vulnerable under Criterion A2. In addition, this species may undergo further declines if the mortality of the species in bycatch of the Skipjack fishery cannot be reduced.
|Range Description:||This species is circumglobal in tropical and temperate seas. It is not found in the Mediterranean.|
Native:American Samoa (American Samoa); Angola (Angola); Anguilla; Antigua and Barbuda; Argentina; Aruba; Australia; Bahamas; Barbados; Belize; Bermuda; Brazil; Brunei Darussalam; Cambodia; Canada; Cape Verde; Cayman Islands; Chile; China; Christmas Island; Cocos (Keeling) Islands; Colombia; Congo, The Democratic Republic of the; Cook Islands; Costa Rica; Côte d'Ivoire; Cuba; Dominica; Dominican Republic; Ecuador; El Salvador; Equatorial Guinea; Falkland Islands (Malvinas); Fiji; French Guiana; French Polynesia; Gabon; Gambia; Ghana; Grenada; Guadeloupe; Guam; Guatemala; Guinea; Guinea-Bissau; Guyana; Haiti; Honduras; Hong Kong; India; Indonesia; Ireland; Jamaica; Japan; Kenya; Kiribati; Korea, Democratic People's Republic of; Korea, Republic of; Liberia; Madagascar; Malaysia; Maldives; Marshall Islands; Martinique; Mauritania; Mauritius; Mexico; Micronesia, Federated States of ; Montserrat; Morocco; Mozambique; Namibia; Nauru; Netherlands Antilles; New Caledonia; New Zealand; Nicaragua; Nigeria; Niue; Norfolk Island; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Pitcairn; Portugal; Puerto Rico; Réunion; Russian Federation; Saint Barthélemy; Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Samoa; Senegal; Seychelles; Sierra Leone; Singapore; Solomon Islands; Somalia; South Africa; Spain; Sri Lanka; Suriname; Taiwan, Province of China; Tanzania, United Republic of; Thailand; Timor-Leste; Tokelau; Tonga; Trinidad and Tobago; Turks and Caicos Islands; Tuvalu; United Kingdom; United States; United States Minor Outlying Islands; Uruguay; Vanuatu; Venezuela, Bolivarian Republic of; Viet Nam; Virgin Islands, British; Virgin Islands, U.S.; Wallis and Futuna; Yemen
|FAO Marine Fishing Areas:||
Atlantic – northeast; Atlantic – eastern central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Pacific – southeast; Pacific – western central; Pacific – northwest; Pacific – eastern central; Pacific – northeast; Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
FAO worldwide reported landings show a gradual increase from 808 tonnes in 1950 to an average of approximately 400,000–450,000 tonnes from 1996–2006 (FAO 2009). There are four stocks that are globally managed for this species. As of 2004, the stocks in the Atlantic and Indian Ocean are considered Fully Exploited, and the Eastern Pacific and Western/Central Pacific stocks are considered Over-exploited (Majkowski 2007). It is assumed that the Bigeye Tuna in the Eastern Pacific comprise a separate stock from the Western Pacific.
Eastern Pacific Ocean
In the Eastern Pacific, annual catches although fluctuating, average 100,000–130,000 tonnes and are increasing. The expansion of the purse seine fisheries in mid 1990s has contributed to this increase in landings (STECF 2007). The stock size in 1993 is estimated to have been 34% of its unexploited size. After 1993, purse seining for tunas associated with fish-aggregating devices (FADs) took significant quantities of small and medium-sized Bigeye Tuna. In 2005, after several years of poor recruitment and excessive levels of fishing mortality, the stock size was estimated to be at about 14% of its unexploited size. Due to recent spikes in recruitment, the current level has increased to 17% (IATTC 2008). Recent catches, such as in 2008, have been above the estimated maximum sustainable yield (MSY) of 84,000 tonnes (ISSF 2010).
Previous analyses indicated that the spawning stock biomass (SSB) was below MSY, and that fishing mortality rates were about 20% greater than those corresponding to the MSY (IATTC 2008, Aires da Silva and Maunder 2007), indicating that the Bigeye Tuna stock in the Eastern Pacific was over-exploited (IATTC 2008). However, according to the most recent stock assessment conducted in 2009 (Aires da Silva and Maunder 2010), fishing mortality rates are estimated to be below the level corresponding to MSY, and the recent levels of spawning biomass are estimated to be above that level (IATTC 2010). However, these results are more pessimistic if a stock-recruitment relationship is assumed, if a higher value is assumed for the average size of the older fish, if lower rates of natural mortality are assumed for adult Bigeye Tuna, and if only the late period of the fishery (1995–2009) is included in the assessment (IATTC 2010). In addition, La Niña events may become stronger and more frequent during the period 2010–2030, and this La Niña dominance may negatively influence recruitment strength of Bigeye Tuna in the Eastern Pacific Ocean (IATTC 2010).
Based on linear regression of SSB estimates from the most recent 2009 stock assessment (Aires da Silva and Maunder 2010), there has been an estimated 18% decline in SSB over the past 15 years (1992–2007) in the Eastern Pacific.
Western and Central Pacific Ocean
The overall trend in the Western Central Pacific Ocean is that biomass declined rapidly during the 1950s and 1960s, was relatively stable through the 1970s and 1980s, and then declined steadily from 1990 onwards (Langley et al. 2008). Adult biomass has declined by at least 20% over the last decade (STECF 2007, Langley et al. 2008). Fishing mortality has increased steadily since the introduction of commercial fishing. Current fishing mortality exceeds FMSY, and it was estimated that a 34–50% reduction from the level of fishing mortality in 2004–2007 would be needed to keep the biomass above the level corresponding to MSY (ISSF 2010). However, current bomass is also greater than BMSY. It was predicted that if fishing mortality continues at current levels, the biomass would be reduced to about half the MSY level (Harley et al. 2010, ISSF 2010).
Based on linear regression of SSB estimates from the most recent 2010 stock assessment (Harley et al. 2010), there has been an estimated 29% decline in SSB over the past 15 years (1992–2007) in the Western and Central Pacific. Currently, this stock is approaching an overfished state, if it is not already slightly overfished (Harley et al. 2010).
In previous assessment conducted in 2005 (Hillary and Mosquiera 2006), spawning stock biomass was estimated to have declined from approximately 180,000 tonnes to about 75,000 tonnes from 1954–2006, and given 2002 levels of fishing mortality and effort, was projected to decline to approximately 50,000 tonnes by 2014 (Hillary and Mosqueira 2006).
Results of an updated assessment conducted in 2009 based on various models (IOTC 2009), showed that results were broadly similar to previous work. Current (2008) exploitation levels for this stock (107,000 t) are within the range of estimated MSY levels (100,000–115,000 t), although catches in the past (1997–1999) have significantly exceeded MSY. Estimated values of fishing mortality and SSB for 2008 are also close to MSY-related values, indicating a fully exploited stock (IOTC 2009). Current spawning stock is estimated to be two billion individuals and 800,000 tonnes (IOTC 2009).
Based on linear regression of SSB estimates from the most recent 2009 stock assessment (IOTC 2009), there has been an estimated 73% decline in SSB over the past 15 years (1992–2007) in the Indian Ocean.
Genetic, tagging and fisheries data suggest this species constitutes a single interbreeding population in the Atlantic. The total catch for this species in the Atlantic increased up to the mid-1970s reaching 60,000 t and fluctuated over the next 15 years. In 1991, catch surpassed 95,000 t and continued to increase, reaching a historic high of about 133,000 t in 1994. Reported and estimated catch has been declining since then and fell below 100,000 t in 2001. This gradual decline in catch has continued, although with some fluctuations from year to year, until the most recent year of data 2009. The preliminary estimate for 2009 is 86,011 t, the highest value in the last five years. This estimate includes preliminary estimates made for a few fleets that have not yet provided data to ICCAT (SCRS ICCAT 2010).
In 2010, the plausible range of MSY estimated from the joint distribution using three types of abundance indices was between 78,700 and 101,600 tons (80% confidence limits) with a median MSY of 92,000 t. Historical estimates show large declines in biomass and increases in fishing mortality, especially in the mid 1990s when fishing mortality exceeded FMSY for several years. In the last five or six years there have been possible increases in biomass and declines in fishing mortality. The biomass at the beginning of 2010 was estimated to be at between 0.72 and 1.34 (80% confidence limits) of the biomass at MSY, with a median value of 1.01 and the 2009 fishing mortality rate was estimated to be between 0.65–1.55 (80% confidence limits) with a median of 0.95 (SCRS ICCAT 2010).
Based on linear regression of total biomass estimates from the most recent 2010 stock assessment (ICCAT 2010), there has been an estimated 40% decline in total biomass over the past 15 years (1992–2007) in the Atlantic Ocean.
|Habitat and Ecology:||
This pelagic and oceanodromous species occurs in waters with temperatures ranging from 13–29°C, but the optimum is between 17°C and 22°C. Variation in occurrence is closely related to seasonal and climatic changes in surface temperature and thermocline. Juveniles and small adults school at the surface in monospecific groups or mixed with other tunas, and may be associated with floating objects. Adults stay in deeper waters (Maigret and Ly 1986). This species is mostly found above 500 m, but can dive deeper. This species feeds on a wide variety of fishes, cephalopods and crustaceans during the day and at night (Collette 1995).
Eggs and larvae are pelagic (Kailola et al. 1993). This species is a multiple spawner that may spawn every one or two days over several months (Nikaido et al. 1992). They spawn over periods of the full moon, and spawn throughout the year in tropical waters (Kailola et al. 1993). Although spawning apparently occurs widely across the equatorial Pacific Ocean, the greatest reproductive potential appears to be in the eastern Pacific, based on apparent maturation, size frequencies, and catch per unit of effort (Kikawa 1966). In the eastern and central Pacific, spawning has been recorded between 15°N and 15°S and between 105–175°W during most months when sea surface temperatures exceeded 24°C with a peak from April through September in the northern hemisphere and between January and March in the southern hemisphere. Spawning is primarily at night between 1900 and 0400 hr. The average mature female spawned every 2.6 days. The estimated mean relative fecundity is 24 oocytes/g body weight. The number of eggs per spawning has been estimated at 2.9–6.3 million (Collette 2010).
Longevity for this species may vary by region. Estimated maximum age for this species in the Western Pacific is 16 years (Farley et al. 2006), in the Indian Ocean is eight years (Tankevich 1982), in the Atlantic Ocean is nine years (Hallier et al. 2005), and in the Eastern Pacific is five years (Schaefer and Fuller 2006).
Age at first maturity is estimated to be about two years (Nootmorn 2004, Farley et al. 2006). However, Calkins (1980) reports a sexual maturity for this species at 100–130 cm at an age of about three years old. Minimum length at sexual maturity for females can be 80–102 cm, and predicted length at 50% maturity of 102–135 cm (approximately 3.5 years of age) has also been reported in different areas. Males tend to dominate the catches over the entire size range (Collette 2010).
The generation length for this species is between 4.4 and five years based on age structure data across different stocks (Collette et al. 2011).
The all-tackle game fish record is of a 197.31 kg fish caught off Cabo Blanco, Peru in 1957 (IGFA 2011) .
Overfishing is occurring primarily in the Western Pacific, with adult biomass having declined about 20% over the past decade (Langley et al. 2008), and if fishing mortality continues at current levels, the biomass is predicted to reduce to about half the MSY level (Harley et al. 2010, ISSF 2010). In addition, this species may undergo further declines if the mortality of the species in bycatch of the Skipjack Tuna fishery cannot be reduced.
In the Pacific, Bigeye Tuna are primarily exploited by longliners from 40°N to 40°S and by purse seiners from 10°N to 20°S. In the Eastern Pacific Ocean there have been substantial changes in the Bigeye Tuna fishery over the last 15 years. Initially, the majority of the Bigeye Tuna catch was taken by longline vessels, but with the expansion of the fishery using fish-aggregating devices (FADs) since 1993, the purse seine fishery has taken an increasing proportion of the Bigeye Tuna catch. The FAD fishery captures smaller Bigeye Tuna, and has therefore reduced the yield per recruit and the maximum sustainable yield (MSY). On average, the fishing mortality of Bigeye Tuna less than four and a half years old has increased substantially since 1993, and that of older fish has increased slightly (IATTC 2008).
In the Indian Ocean, Bigeye Tuna is mainly caught by industrial purse seine and longline fisheries and appears only occasionally in the catches of other fisheries. However, in recent years the amounts of Bigeye Tuna caught by gillnet fisheries are likely to be considerably higher due to the major changes experienced in some of these fleets, notably changes in boat size, fishing techniques and fishing grounds. In recent years catches of Bigeye Tuna in the western Indian Ocean have dropped considerably, especially in areas off Somalia, Kenya and Tanzania and in particular in 2008 and, especially, 2009. The drop in catches is the consequence of a drop in fishing effort in the area of both purse seine and longline fisheries, due to the effect of piracy in the western Indian Ocean region, while catches are increasing in the eastern Indian Ocean probably due to the shift of some longline fleet in the areas because of the piracy activities along the Somalia area (IOTC 2010).
In the Atlantic this stock is exploited by three major gears/fisheries: longline (50–60%), purse seine (25%) and pole-and-line (15%) (ISSF 2010). Although there are a number of data uncertainties, including a lack of data on illegal, unregulated and unreported (IUU) fishing, stock assessment models estimate the MSY to be between 90,000-93,000 tonnes (ISSF 2010). Based on these projections, biomass is expected to rebuild to the MSY level in a few years if catches are maintained at or below 85,000 tonnes. It is important to note the use of high-tech FADs in the Gulf of Guinea and increases in effort due to vessels coming from the Indian Ocean, will increase already high levels of fishing mortality of juvenile Bigeye Tuna.
This species is listed as a highly migratory species in Annex I of the 1982 Convention on the Law of the Sea (FAO Fisheries Department 1994).
In the Pacific, several countries such as Ecuador, Colombia and Peru have created closures for this species. The vast majority of the catch is from Ecuador in this region. SPC made a recommendation to reduce catches in the Pacific. In Taiwan, the fleet has been reduced by 183 Bigeye long-line vessels (which is more than 30% of fishing capacity) (IATTC 2008). As of December 2009, NOAA has put into place catch limits for US pelagic longline fisheries in Western and Central Pacific Ocean for 2009, 2010 and 2011 having determined that the Pacific Ocean population is subject to overfishing. Under this rule, the U.S. will reduce its longline catch of Bigeye Tuna from the 2004 baseline catch of 4,181 metric tons (mt) to 3,763 mt.
In the Atlantic, the Scientific, Technical and Economic Committee for Fisheries (STECF) recommends that the total catch does not exceed 85,000 t (STECF 2009). Recommendation 04-01 also implemented a new, smaller closure for the surface fishing in the area 0–5ºN, 10–20ºW during November in the Gulf of Guinea.
|Citation:||Collette, B., Acero, A., Amorim, A.F., Boustany, A., Canales Ramirez, C., Cardenas, G., Carpenter, K.E., Chang, S.-K., Chiang, W., de Oliveira Leite Jr., N., Di Natale, A., Die, D., Fox, W., Fredou, F.L., Graves, J., Viera Hazin, F.H., Hinton, M., Juan Jorda, M., Minte Vera, C., Miyabe, N., Montano Cruz, R., Nelson, R., Oxenford, H., Restrepo, V., Schaefer, K., Schratwieser, J., Serra, R., Sun, C., Teixeira Lessa, R.P., Pires Ferreira Travassos, P.E., Uozumi, Y. & Yanez, E. 2011. Thunnus obesus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 13 December 2013.|
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