2.1.10.2 BLT

CHAPTER 2.1.10.2 AUTHORS: LAST UPDATE: BULLET TUNA J. VALEIRAS and E. ABAD Sept. 4, 2006

2.1.10.2 Description of Bullet Tuna (BLT)

1. Names

1.a Classification and taxonomy

Species name: Auxis rochei (Risso 1810) ICCAT species code: BLT ICCAT names: Bullet tuna (English), Bonitou (French), Melvera (Spanish)

According to Collette and Nauen (1983), the bullet tuna is classified as follows:

• Phylum: Chordata • Subphylum: Vertebrata • Superclass: Gnathostomata • Class: Osteichthyes • Subclass: Actinopterygii • Order: Perciformes • Suborder: Scombroidei • Family: Scombridae

Some authors have used the name Auxis thazard as including Auxis rochei in the belief that there was only a single worldwide species of Auxis (Collette and Nauen 1983).

1.b Common names

List of vernacular names used according to ICCAT, FAO and Fishbase (www.fishbase.org). The list is not exhaustive and some local names might not be included.

Albania: Skumri i madh. Australia: Long corseletted frigate mackerel, Maru frigate mackerel. Azores Islands: Bullet mackerel, Bullet tuna, Frigate mackerel, Judeu. Barbados: Blow goat, Frigate mackerel. Brazil: Bonito-cachorro, Cavala. China Main: 㞬㫅⯦㫎. Chinese Taipei: ⰼ↮, ᅭⰼ㫎, ↮௘㨶. Cuba: Melva aleticorto. Denmark: Fregatmakrel. Ecuador: Botellita. France: Auxide, Bonitou. Germany: Fregattmakrele. Greece: ȉȠȣȝʌĮȡȑȜȚ, ȀȠʌȐȞȚ, ȀȠʌĮȞȑȜȚ, ǺĮȡİȜȐțȚ, ȉİȡȞȑIJIJĮ, Kopani, Koponi-Kopanaki. India: , Bullet-tuna, Eli-choorai, Kutteli-choorai, Ragondi, Urulan-choorai. Italy: Tombarello. Japan: Chiboh, Dainanpo, Kobukura, Kogatsuo, Kubarai, Magatsuwo, Manba, Mandara, Marugatsuwo, Marumejika, Marusöda, Marusôda, Marusödakatsuo, Mejika, Nodoguro, Rohsoku, Soda, Soku, Subo, Subota, Uzawa. Libya: ϱΘϴδΗΎϣ, Matseti. Madeira Island: Judeu. Malaysia: Aya selaseh, Bakulan, Kayu, Tongkol. 209 ICCAT MANUAL, 1st Edition (January 2010)

Malta: Bizu, Mazzita, Pizzintun, Sgamirru, Tombitombi, Tumbreall, Tumbrell, Zgamirru. Mexico: Bonito, Melva, Melvera. Micronesia: Mackerel tuna, Yasiuneiu-yauma. Mozambique: Judeu melveira. Nicaragua: Melvera. Norway: Auxid. Papua New Guinea: Bullet tuna. Peru: Barrilete negro. Philippines: Aloy, Bodboran, Bodboron, Bonito, Buboron, Budburon, Bullet tuna, Buroboto bilog, Burot, Frigate tuna, Kuringding, Lubak-lubak, Mangko, Manko, Perit, Pidlayan, Pirit, Tangi, Tulingan, Turingan, Vahuyo. Poland: Tazar marun. Portugal: Judeu. Slovenia: Trupec. South Africa: Bullet tuna, Koeël-tuna. Spain: Melva, Melvera. Sri Lanka: Eli-choorai, Kutteli-choorai. St Helena: Mackerel tuna. Sweden: Auxid. Turkey: Gobene baligi, Tombik baligi. United Kingdom: Bullet tuna, Frigate mackerel, Frigate tuna. Uruguay: Bullet tuna, Sanguzo. United States of America: Bullet mackerel, Bullet tuna. Vietnam: Bullet tuna, Cá Ngӯ o.

2. Identification

Figure 1. Drawing of an adult Auxis rochei (by A. López ‘Tokio’).

Characteristics of Auxis rochei (see Figure 1 and Figure 2)

Bullet tuna is a small tuna species. Maximum size in east Atlantic is 51 cm fork length (Neves dos Santos and García 2006). In the Gibraltar Strait is 47 cm fork length and about 1.9 kg weight (Rodríguez-Roda 1966). Common size is 35 cm (Collete and Nauen 1983; Collete 1986).

Colour:

• Colour bluish iridescence on dorsal parts turning to deep purple or almost black on the head.

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x Pattern of 15 or more dark bars or wavy lines, oblique to nearly vertical, in the scaleless area above lateral line. x White belly without stripes or spots. x Pectoral and pelvic fins are purple, with black inner sides. x Black patch at postero-ventral border of eye.

External:

x Body robust elongate and rounded. x Body naked, except for the corselet which is well developed. Corselet wide in its posterior part (more than 6 scales wide under second dorsal fin origin, usually 10 to 15). x Strong median keel on each side of caudal peduncler, between two smaller keels. x Two dorsal fins separated by a large interspace (at least equal to length of first dorsal fin base). Second dorsal lower than first, followed by 8 finlets. x Anal fin followed by 7 finlets. x Short pectoral fin which does not reach the beginning of scaleless area above corselet. Pectoral rays: 22- 25. x Dorsal spines: 10-12. x Gillrakers on first arch: 38-47. x Inter-pelvic process single and very large, equal to length of pelvic fins.

Internal:

x Swimbladder absent. x Right lobe of liver very long, extending the length of the body cavity and left lobe greatly reduced. x Vertebrae: 39. x Cutaneus artery present but divided into separate dorsal and ventral branches. The ventral branch is very poorly developed.

Pattern of 15 or more dark bars or wavy lines, oblique to nearly vertical, in the scaleless area above lateral line

Strong median keel on each side of caudal peduncler, between two Short pectoral fin which does not reach the beginning of scaleless smaller keels area above corselet

Figure 2. Synthesis of the most outstanding characteristics of Auxis rochei (by A. López ‘Tokio’).

3. Distribution and population ecology

3.a Geographical distribution

The genus Auxis is distributed worldwide in tropical and subtropical waters. The confusion surrounding the identification of the species of Auxis is reflected in their reported distribution in the world’s oceans. Auxis is distributed in both sides of the tropical and subtropical Atlantic Ocean, including the Mediterranean, Caribbean Sea and Gulf of Mexico (Figure 3). Latitudinal range reported for genus in Atlantic is from 45ºN to 35ºS.

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In the eastern Atlantic is reported as far north as Norway and as far south as South Africa waters. In the western Atlantic off the east coast of North America has been recorded from Gulf of Maine, (Cape Cod). Off the Atlantic coast of South America the species is recorded to Mar del Plata (Argentina).

Figure 3. Geographical distribution of Auxis sp. (FAO. c2001-2009. Compilation of aquatic species distribution maps of interest to fisheries. In FAO Fisheries Department [online]. Rome. [15 sept. 2009]. http://www.fao.org/fishery/collection/fish_dist_map).

3.b Habitat preferences

Bullet tuna is an epipelagic and neritic fish as well as oceanic occurring in warm waters. Larvae have a high temperature tolerance of at least 21.6 to 30.5ºC, (the widest among tuna species studied), their optimum is 27- 27.9ºC.

The species has a strong schooling behaviour.

3.c Migrations Information concerning to migration patterns is scarce and fragmented (Rey and Cort 1981). Several authors have suggested a genetic migration from the Atlantic Ocean to the spawning areas in the Mediterranean trough the Gibraltar Strait (Sabatés and Recasens 2001).

3.d Recruitment Knowledge of the early life stages in tunas is very scarce. It is assumed that larval period is short. During the first life stages bullet tuna are not caught and juvenile life history is unknown. Immature fish first appear in fishery from around 25 cm of fork length.

4. Biology

4.a Growth Bök and Oray (2001) studied age and growth by otoliths and dorsal spines analysis and found five age groups (0- 4) for the Aegean Sea and the eastern Mediterranean. Von Bertalanffy growth parameters are showed in Table 1. Rodriguez-Roda (1983) studied vertebrae of 27 bullet tuna from Atlantic area near Gibraltar strait and found four age groups (1-4).

212 2.1.10.2 BLT

Table 1. Growth parameters for bullet tuna (L’LQFP.LQ\-1, t0 in y).

Growth Parameter Area Country Reference N FL range Method

L’ kt0 (cm) 45.26292 0.39722 -1.6044 Aegean Sea and Eastern Turkey Bök and Oray, 2001 630 28.5-44.5 Dorsal spine, Mediterranean otoliths 45.08422 0.33988 -1.5984 Aegean Sea and Eastern Turkey Bök and Oray, 2001 311 males 30-44.5 Dorsal spine, Mediterranean otoliths 47.76151 0.29235 -2.3649 Aegean Sea and Eastern Turkey Bök and Oray, 2001 309 females 32.6-44.5 Dorsal spine, Mediterranean otoliths

4.b Length-Weight relationship

Published length-weight relationships for several geographical areas in Atlantic are showed in Table 2.

Table 2. Published bullet tuna length-weight relationships.

Equation N FL range (cm) Sex Area Country Reference W= 0.0076 x FL 3.24 936 28.5-44.5 All Aegean Sea and Eastern Turkey Bök and Oray, 2001 Mediterranean W= 0.000156 x FL 4.29 311 30-44.5 Male Aegean Sea and Eastern Turkey Bök and Oray, 2001 Mediterranean W= 0.000719 x FL 3.89 309 32.6-44.5 Female Aegean Sea and Eastern Turkey Bök and Oray, 2001 Mediterranean W= 0.00001005 x FL 3.12987 744 34-45 All Gibraltar Strait Spain Rodríguez-Roda, 1966 W= 0.00559 x FL 3.29 458 25.9-47 All Western Mediterranean Spain Macías et al., 2006

4.c Reproduction

Spawning

This species is a multiple spawner with asynchronous oocyte development that carried out several spawning step by reproductive season (Niiya, Y, 2001; Macías et al. 2005).

The spawning season may vary from region to region depending on the hydrographical regime: in many parts of the Mediterranean and in the Straits of Gibraltar, maturing fish are common from May onwards, and more than 30% are spent by September. The spawning period in the Mediterranean has been reported to occur from June to September (Ehrenbaum 1924; Piccinetti et al. 1996; Alemany 1997; Macías et al. 2005).The spawning period of this species in the Aegean Sea and in the Mediterranean Sea was determined to be from March to September (Bök and Oray 2001). In western African coasts the spawning occurs from April to June in the gulf of Guinea and September-October to March off Congo and Angola (Rudomiotkina 1984).

In large areas of the Gulf of Mexico, peaks of batch spawning are reported from March to April and from June to August, while in the coastal waters from Cape Hatteras to Cuba and in the Straits of Florida, the spawning season begins in February.

Maturity

Fork length at first maturity off Gibraltar is 35 cm in females and 36.5 cm in males (Rodriguez-Roda 1966). In the Aegean and in the Mediterranean Seas, Auxis rochei reached the sexual maturity at 34.4 cm length and the development of the gonads is almost the same for both genders. The gonads are mature after the month of March for most of the male or female individuals (Bök and Oray 2001).

Sex ratio

The sex ratio in Aegean Sea is approximately 1:1 (Bök and Oray 2001). Macías et al. (2005) found a sex ratio of 1:1.7 at western Mediterranean catches.

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Fecundity

This species is a fish with indeterminate fecundity (Macías et al. 2005). In the Mediterranean the average fecundity. The average fecundity is 233941 oocytes by spawning batch (Macías et al. 2006).

4.d First life stages

Eggs and Larvae

Eggs are pelagic, 0.82-0.88 mm of diameter and with one oil globule (0.24-0.25 mm of diameter). The yolk is homogeneus. The hatch size is 2.14 mm. The embryo presents melanophores, green chromatophores and 6-14 stellate chromatophores on oil globule. Larvae present pigmentation on midbrain, hindbrain, gut, cleithral symphysis dorsal and ventral margins of tail (Richards 2005).

4.e Diet

Food is primarily selected by the size of gillrakers. The species feeds on fish, crustaceans, cephalopods and others. Fish prey largely of small pelagic fishes, particularly anchovies and other clupeoids (Etchevers 1957). Crustaceans are especially planktonic crustaceans as megalops and stomatopods larvae.

Predators: several tuna species, pelagic sharks, billfishes and big pelagic fish (Coryphaena hippurus, Alepisaurus sp, Sphyraena sp.). Because of its abundance, they are considered an important element of the food chain, being a forage prey for other commercial species (Olson 1982).

4.f Physiology

There is a lack on information on this topic.

4.g Behaviour

This species makes large schools of similar sized individuals. Often mixes with Auxis thazard in same school.

4.h Natural mortality

There is a lack on information available on this biological parameter.

5. Fisheries biology

5.a Populations/Stock structure

There is little information available to determine the stock structure of bullet tuna. Current information does not allow for an evaluation of stock status.

5.b Description of fisheries: catches and effort

Bullet tuna is exploited mainly by surface gears and artisanal fisheries as trolling lines, handlines, small-scale longlines, and a wide variety of nets, especially traps, gill or drift nets, ring nets, beach seines, otter trawls, and purse seines. In some of these fisheries, Auxis species are taken incidentally as by-catch as in purseseine fisheries for yellowfin and skipjack tuna.

In the Atlantic, catches of Auxis species are usually not identified to species. Thus in the total catch of frigate tuna, the proportion of each of the two species is not known. However, almost the entire Venezuela, Atlantic and Mediterranean catch is supposedly Auxis rochei (Collette and Nauen 1983).

Annual catches reach 3,634 t in 1990 (Figure 4). Average estimated landings from 1980 to 2004 is 581 t. Unknown quantities of bullet tuna are landing and recorded as frigate tuna in the Atlantic (ICCAT 2006).

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BLT

4000

3500

3000

2500

2000

1500 1000 500 0

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year

Figure 4. Catch distribution of bullet tuna in the Atlantic Ocean for 1980-2004 (t).

6. Bibliography ALEMANY, F. 1997. Ictioplancton del Mar Balear. Ph. D. thesis, Univ. Illes Balears. BÖK, T. and K. Oray, 2001. Age and growth of bullet tuna Auxis rochei (Risso 1810) in Turkish waters. Col. Vol. Sci. Pap. ICCAT, 52: 708-718. COLLETE, B. B. 1986. Scombridae. In: P.J.P. Whitehead, M.-L. Bauchot, J.-C. Hureau, J. Nielsen, and E. Tortonese (eds.), Fishes of the North-eastern Atlantic and the Mediterranea. Vol II. pp. 981-997. Unesco, Paris. COLLETTE, B. B. and C. E. Nauen., 1983 FAO species catalogue. Vol. 2. Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. FAO Fish. Synop. 125(2). 137 pp. EHRENBAUM, E. 1924. Scombriformes. Report on the Danish Oceanografical Expeditions 1908-1910. Mediterranean and Adjacent Seas, 2 (A, 11). ETCHEVERS, S. L., 1976. Incidencia de clupeoideos en la alimentacion de las caballas: Euthynnus alletteratus (Rafinesque 1976) y Auxis thazard (Lacepède) en la costa noreste de Margarita. Lagena (37-38):9-11. ICCAT, 2006. Report for biennial period, 2004-05 Part II (2005), Vol. 2, Executive Summaries on species: Small Tunas: 128-135. MACÍAS, D., Gómez-Vives, M. J,. de la Serna, J. M., 2005. Some reproductive aspects of bullet tuna (Auxis rochei) from the south western Spanish Mediterranean. Collect. Doc. Cient. Vol. ICCAT, 58(2): 484-495. MACÍAS, D., Lema, L., Gómez-Vives M. J., and J. M. de la Serna, 2006. A preliminary approach to the bullet tuna (Auxis rochei) fecundity in the Spanish Mediterranean. Collect. Vol. Sci. Pap. ICCAT, 59(2): 571-578. MACÍAS, D., Lema, L., Gómez-Vives, M. J., Ortiz de Urbina, J. M. and de la Serna, J. M., 2006. Some biological aspects of small tunas (Euthynnus alletteratus, Sarda sarda & Auxis rochei) from the south western Spanish Mediterranean traps. Collect. Vol. Sci. Pap. ICCAT, 59(2): 579-589. NEVES DOS SANTOS, M. and A. García, 2006. Observations on the catches of small tunas from a trap off the Algarve (southern Portugal). Collect. Vol. Sci. Pap. ICCAT, 58: in press. NIIYA, Y. 2001. Maturation cycle and batch fecundity of the bullet tuna, Auxis rochei, off Cape Ashizuri, southwestern Japan. Nippon Suisan Gakkaishi, 67 (1): 10-16. Jan 2001. OLSON, R. J., 1982. Feeding and energetics studies of yellowfin tuna; food for ecological thought. Col. Vol. Sci. Pap. ICCAT, 17:444-57. PICCINETTI, C., Piccinetti-Manfrin, G. and Soro, S. 1996. Larve di Tunnidi in the Mediterranean. Biol. Mar. Medit., 3: 303-309. REY, J. C. and Cort, J. L., 1981. Contribution à la conaissance de la migration des Escombridae en Mediterranée Occidentale. Rapp. P-V, Commn. Int. Explor. Scient. Mer Méditerr., 27: 97-98.

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RICHARDS, W. J., (ed.), 2005. Early Stages of Atlantic Fishes: An identification guide for the western central North Atlantic. CRC Press, Taylor and Francis Group, Boca Raton, FL, 2640 pp. RODRÍGUEZ-RODA, J. 1966. Estudio de la bacoreta, Euthynnus alletteratus (Raf.), bonito, Sarda sarda (Bloch) y melva Auxis thazard (Lac.), capturados por las almadrabas españolas. Invest. Pesq. 30: 247-92. RODRÍGUEZ-RODA, J., 1983. Edad y crecimiento de la melva, Auxis rochei (Risso), del Sur de España. Invest. Pesq. (Barc.), 47(3): 397-402. RUDOMIOTKINA, G. P., 1984. New data on reproduction of Auxis spp. In the Gulf of Guinea. Collect. Vol. Sci. Pap. ICCAT, 20(2): 465-468. SABATÉS, A. and Recasens, L. 2001. Seasonal distribution and spawning of small tunas, Auxis rochei (Risso) and Sarda sarda (Bloch) in the northwestern Mediterranean. SCI. Mar., 65 (2): 95-100. UCHIDA, R. N., 1981. Synopsis of biological data on frigate tuna, Auxis thazard, and bullet tuna, A. rochei. NOAA Tech. Rep. NMFS Circ., (436):63 p. Issued also as FAO Fish. Synop., (124): 63 p.

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