Allothunnus Fallai Research Articles

Age and growth of slender tuna (Allothunnus fallai) in an unexploited temperate population.

Many large predatory fishes are in decline and tuna sustainability is high on the global agenda. Slender tuna (SLT), Allothunnus fallai, is data-poor and a rare contemporary example of a globally unexploited temperate tuna. This study analysed 214 otoliths for age and growth of fish collected in the South Atlantic. Observed ages varied between 9 and 42 years for a size range of 68-90 cm fork length. We reveal important life history data for SLT before exploitation and underline the relevance of data-poor stocks in understanding wider questions for exploited tuna.

The Role of Slender Tuna, Allothunnus fallai, in the Pelagic Ecosystems of the South Pacific Ocean

Gonad condition and stomach contents were examined in 2257 specimens of Allothunnus fallai (463-896 mm fork length) caught by surface driftnets from the high seas of the South Pacific (20-54 o S, 74-150 o W) during 1985-1987. Subtropical waters and the Peru Current north of 31 o S were considered to be the spawning grounds of slender tuna during October, November and December. From November to February, feeding grounds were located in subantarctic waters and the Peru Current south of 38 o S, where slender tuna preyed mainly upon euphausiids, squids, copepods, young myctophid fish and amphipods. The dominant species in the diets were Euphausia vallentini, E. lucens, Thysanoessa gregaria and Neocalanus tonsus throughout the subantarctic waters. Young of the squid, Martialia hyadesi, dominated in the Southeast Pacific and Moroteuthis spp. were common in the subantarctic waters of the central South Pacific. Hyperiid amphipods, Primno macropa and Themisto gaudichaudii, were common but gravimetrically much less important in the diet. Adult slender tuna were preyed upon by Isurus oxyrinchus, Prionace glauca, Xiphias gladius and Makaira mazara in subtropical waters, but not so in subantarctic waters. Allothunnus fallai was considered to be a highly migratory species, with a life-style adapted to the seasonally fluctuating biomass of zooplankton in subantarctic epipelagic waters

Records of Juveniles of Slender Tuna, Allothunnus fallai, from the Equatorial Western Pacific and the South Atlantic Oceans

Records of Juveniles of Slender Tuna, Allothunnus fallai, from the Equatorial Western Pacific and the South Atlantic Oceans

Elevated red myotomal muscle temperatures in the most basal tuna species, Allothunnus fallai

The present study tested the hypothesis that Allothunnus fallai can elevate its slow‐oxidative red myotomal muscle (RM) temperature. Measurements on 30 A. fallai (750–850 mm fork length) captured by hook and line off the coast of southern New Zealand revealed that RM temperatures are elevated by mean ±s.d. 8·1 ± 1·3° C (range 6·7–10·0° C) above the mean ±s.d. ambient sea surface temperature 15·3 ± 0·8° C (range 14·3 to 16·4° C). These data provide evidence that the vascular modifications to the central circulation of A. fallai act as a counter‐current heat exchanger and that RM heat conservation is a character state present in all extant tuna species.

Southernmost occurrence of the slender tuna, Allothunnus fallai, off Tierra del Fuego, South Atlantic Ocean

The slender tuna, Allothunnus fallai Serventy 1948, is an epipelagic scombrid with a circumglobal distribution in the Southern Ocean from about 20–50 S (Warashina and Hisada 1972; Collette and Nauen 1983), south to 54 S in the South Pacific (Yatsu 1995), with three exceptions from the North Pacific (Schaefer and Childers 1999). Recently, an adult male, 784-mm fork length (Fig. 1) was taken further south in the South Atlantic, at 53 250S, 64 230W off Tierra del Fuego, Argentina. It was caught while trawling at 167 m on March 12, 2007 by the fishing vessel Tai An. The surface water temperature was 8 C and the salinity 33.59 parts per thousand (ppt). The specimen has been deposited in the fish collection of the Instituto Nacional de Investigacion y Desarrollo Pesquero under number INIDEP 801. Measurements and counts (Table 1) follow the methods of Collette and Chao (1975) and Schaefer and Childers (1999). External characters agree with descriptions given by previous authors (Serventy 1948; Collette and Chao 1975; Collette and Nauen 1983; Schaefer and Childers 1999). The elongate and rounded shape of the body and the lack of body markings (Fig. 1) are characteristic of this species. Fin-ray and especially, gill-raker counts of 74 confirm the identification. Slender tuna make seasonal migrations from subantarctic and transitional waters to subtropical waters, coupled to seasonal geographic shifts in biomass of epipelagic subantarctic zooplankton (Yatsu 1995). Slender tuna appear to spawn in subtropical waters and in the Peru Current, from approximately 20–30 S, October–December at sea-surface temperatures of 17–25 C (Watanabe et al. 1966; Yatsu 1995). Juveniles are principally encountered between 20 and 35 S at surface temperatures ranging from 19 to 24 C. With increasing size, they gradually move into higher latitudes where water temperatures are lower. Distributions of three species of scombrids are concentrated in the Southern Ocean (Warashina and Hisada 1972; Collette and Nauen 1983; Collette et al. 2001): A. fallai; the butterfly mackerel, Gasterochisma melampus Richardson 1845; and the southern bluefin tuna, Thunnus maccoyii (Castelnau 1872). All species of the tribe Thunnini, except for Allothunnus Serventy 1948, have counter-current heat exchanger systems that allow them to retain body heat generated by muscular contractions thus keeping their bodies warmer than the surrounding sea temperature (Graham and Dickson 2000). Gasterochisma Richardson, 1845 has a layer of fat under the scales and has a brain heater that may be involved in keeping them warm. Recently Sepulveda et al. (2007) showed that Allothunnus also has a heater, extraocular muscles that differ from other tunas and serve as a heater organ that can raise cranial temperatures about 4.8 C above ambient sea temperature. Also, the small central vascular plexus of Allothunnus may be capable of conserving metabolic heat generated by continuous swimming to elevate red muscle temperatures (Graham and Dickson 2000) but body temperatures of Allothunnus are as yet unreported. B. B. Collette (&) National Marine Fisheries Systematics Laboratory, Smithsonian Institution, National Museum of Natural History, P.O. Box 37012, Washington, DC 20013-7012, USA e-mail: collettb@si.edu

Cranial endothermy and a putative brain heater in the most basal tuna species, Allothunnus fallai

Field studies on the slender tuna Allothunnus fallai revealed cranial temperatures that were 4·8 ± 0·4° C (mean ±s.d.) above the ambient sea surface temperature. Dissections aimed at documenting the cranial heat source revealed a fused extraocular muscle complex positioned beneath the brain of this basal tuna species. The muscle complex is structurally distinct from that documented for any other fish species. In A. fallai, all four extraocular rectus muscle pairs (superior, inferior, medial and lateral rectus) are incorporated into one distinct tissue complex which is positioned between the orbits and in direct contact with the braincase. A combination of morphological, physiological and biochemical techniques were used to characterize the modified muscle tissue, and high‐resolution magnetic resonance imaging was used to illustrate its association with the brain and optic nerves. The modified eye muscles lack organized contractile proteins and are perfused by an extensive vascular counter‐current system that originates from the internal carotid artery. Vessel diameters, artery–vein configuration, and anatomic position between the systemic circulation and the warm eye muscles all suggest that this system is a heat exchanger. Collectively, these findings suggest that A. fallai has evolved extraocular muscles that may function to warm the brain and eye region. This is the first record of a cranial modification comprised of all four rectus muscles and the only documented occurrence of this mechanism for cranial endothermy among the tunas.

The evolution of thunniform locomotion and heat conservation in scombrid fishes: New insights based on the morphology ofAllothunnus fallai

Two significant functional differences—a more anterior and internally positioned red myoÍtomal muscle mass and modification of the red-muscle vascular supply to form counter-current heat exchangers—distinguish the tunas (tribe Thunnini) from other species in the teleost family Scombridae. Neither of these characteristics is found in the bonitos (tribe Sardini), the sister group to the Thunnini. The most recent scombrid classification places the slender tuna, Allothunnus fallai, in the tribe Sardini, but some earlier studies suggested that this species should be a member of the Thunnini. Allothunnus fallai does not possess the lateral subcutaneous arteries and veins or the lateral heat-exchanging retia typical of tunas. However, we have found that this species has a highly modified central circulation (dorsal aorta, post cardinal vein, and associated branch vessels) similar to the central heat-exchanging retia of certain tunas, an enlarged haemal arch to accommodate this structure, and the anterior, internal placement of red muscle characteristic of tunas. With these new characters, phylogenetic reconstructions based on parsimony place A. fallai as the sister taxon to the tunas, establish that it is the most basal tuna species, and support the hypothesis that the derivation of tunas from a bonito-like ancestor occurred through selection for an integrated set of characteristics affecting locomotion and endothermy. The major features of this hypothesis are as follows. (1) Selection for continuous, steady, and efficient swimming resulted in changes in body shape (the result of enlargement of the anterior myotomes, the anterior and internal shift of red muscle, and a narrowing of the caudal peduncle) which increased streamlining and led to the adoption of the thunniform swimming mode unique to the tunas. (2) Alterations in blood supply necessitated by the anterior shift in red muscle led to the interdigitation of numerous arterial and venous branches which set the stage for heat conservation. (3) The evolution of endothermy, together with thunniform swimming, contributed significantly to the ecological radiation and diversification of tunas during the Early Tertiary Period. Our studies of A. fallai thus suggest that the shift in red muscle position and changes in central circulation preceded the evolution of red-muscle endothermy. Co-evolutionary changes in red muscle quantity and distribution and in vascular specializations for heat conservation have led to different macroevolutionary trajectories among the now five genera and 14 tuna species of tunas and appear to reflect the influence of changing paleocological and paleoceanographic conditions, including cooling, that occurred in the Tertiary.

The evolution of thunniform locomotion and heat conservation in scombrid fishes: New insights based on the morphology of Allothunnus fallai

Two significant functional differences—a more anterior and internally positioned red myoItomal muscle mass and modification of the red-muscle vascular supply to form counter-current heat exchangers—distinguish the tunas (tribe Thunnini) from other species in the teleost family Scombridae. Neither of these characteristics is found in the bonitos (tribe Sardini), the sister group to the Thunnini. The most recent scombrid classification places the slender tuna, Allothunnus fallai, in the tribe Sardini, but some earlier studies suggested that this species should be a member of the Thunnini. Allothunnus fallai does not possess the lateral subcutaneous arteries and veins or the lateral heat-exchanging retia typical of tunas. However, we have found that this species has a highly modified central circulation (dorsal aorta, post cardinal vein, and associated branch vessels) similar to the central heat-exchanging retia of certain tunas, an enlarged haemal arch to accommodate this structure, and the anterior, internal placement of red muscle characteristic of tunas. With these new characters, phylogenetic reconstructions based on parsimony place A. fallai as the sister taxon to the tunas, establish that it is the most basal tuna species, and support the hypothesis that the derivation of tunas from a bonito-like ancestor occurred through selection for an integrated set of characteristics affecting locomotion and endothermy. The major features of this hypothesis are as follows. (1) Selection for continuous, steady, and efficient swimming resulted in changes in body shape (the result of enlargement of the anterior myotomes, the anterior and internal shift of red muscle, and a narrowing of the caudal peduncle) which increased streamlining and led to the adoption of the thunniform swimming mode unique to the tunas. (2) Alterations in blood supply necessitated by the anterior shift in red muscle led to the interdigitation of numerous arterial and venous branches which set the stage for heat conservation. (3) The evolution of endothermy, together with thunniform swimming, contributed significantly to the ecological radiation and diversification of tunas during the Early Tertiary Period. Our studies of A. fallai thus suggest that the shift in red muscle position and changes in central circulation preceded the evolution of red-muscle endothermy. Co-evolutionary changes in red muscle quantity and distribution and in vascular specializations for heat conservation have led to different macroevolutionary trajectories among the now five genera and 14 tuna species of tunas and appear to reflect the influence of changing paleocological and paleoceanographic conditions, including cooling, that occurred in the Tertiary.

Spatial distribution of planktivorous fish schools in relation to krill abundance and local hydrography off Otago, New Zealand

Side-scan sonar allows mapping of near-surface schools of fish, but it has seldom been used for this purpose. Data were collected off the coast of Otago, New Zealand for 21 days during 1994 to 1996 using a 130 kHz Klein 595 digital side-scan sonar. A total of 2198 schools were detected. Of these, 348 schools of barracouta ( Thyrsites atun), 67 schools of jack mackerel ( Trachurus murphyi), and 17 schools of slender tuna ( Allothunnus fallai) were identified. Barracouta schools were significantly smaller than schools of jack mackerel or slender tuna, but the size of schools was not related to state of tide, location, water depth, salinity, temperature, or density of krill. Fish schools were detected throughout daylight hours, but dispersed at night. Analysis of stomach contents revealed barracouta, jack mackerel and slender tuna were feeding on krill, Nyctiphanes australis, and fish schools occurred in areas with high densities of N. australis. Variability in the abundance of N. australis was related to salinity; catches were highest in a band of low-salinity water which was present in the study area following periods of high river runoff.

Goussia auxidis (Dogiel, 1948) (Apicomplexa: Calyptosporidae) from tuna (Pisces: Scombridae) in the South Pacific

Abstract. A coccidian identified as Goussia auxidis (Dogiel, 1948) is recorded for the first time from the liver and spleen of albacore, Thunnus alalunga; the liver of slender tuna, Allothunnus fallai, skipjack tuna, Katsuwonus pelamis and yellowfin tuna, T. albacares: and in the spleen of Scomber australasicus. All host fish were caught in the western and central South Pacific Ocean. Coccidian spores were not found in the liver of southern bluefin tuna, T. maccoyii, or butterfly tuna, Gasterochisma melampus.

Redescription of the slender tuna,Allothunnus fallaiServenty, and deletion of the scombridScomberomorus(=Cybium)guttatus(Bloch and Schneider) from the New Zealand fauna

Abstract Allothunnus fallai Serventy is redescribed from New Zealand specimens, and the scombrid fish from the Chatham Islands recorded as Cybium guttatum (Bloch and Schneider) and Scomberomorus guttatus (Bloch and Schneider) is described and shown to be a juvenile specimen of Allothunnus fallai. This is the first record of the species from the Chathams area.

Frigate tunaAuxis thazardin New Zealand waters (note)

Abstract Previous records of the frigate tuna Auxis thazard (Lacépède, 1802) were probably misidentifications of the slender tuna Allothunnus fallai. Frigate tuna were caught on the north‐east coast of New Zealand during 1975–76; the modal fork length of 176 specimens was 32–34 cm, and more detailed morpho‐metry and counts from 4 specimens are presented.

Lipid Composition of Slender Tuna (Allothunnus fallai) as Related to Lipid Composition of Their Feed (Nyctiphanes australis)

The depot lipids of specimens of slender tuna (Allothunnus fallai) were characteristic of the zooplankton (Nyctiphanes australis) on which each was feeding. The lipids of the "krill" and of the depot fats were unusually rich in eicosaenoic and docosahexaenoic acids, although the fatty acid composition of samples of "krill" from individual tuna stomachs varied markedly and this variation was reflected in the fatty acid composition of the tuna depot lipids.Because of the nature of their diet, the composition of the depot lipids of the slender tuna varied significantly from those of other tuna species. However, the liver lipids of the slender tuna were more characteristic of all fish liver oils.

Juvenile slender tuna from New Zealand (note)

Abstract Two juvenile slender tuna Allothunnus fallai Serventy, 278 mm and 282 mm fork length, were identified from a catch by a purse seiner 23 km off the Moko Hinau Islands, New Zealand, on 23 January 1974. As the slender tuna were observed to school in association with skipjack tuna Katsuwonus pelamis L., it is probable that adults also school, and could be available as a yet unexploited resource to New Zealand fishermen, especially to the south‐east of New Zealand.

Slender tuna (Allothunnus fallai Serventy): first record of bulk catches, Tasmania, 1974

Purse seine catches of 230 tonnes of slender tuna in Tasmania were made in June 1974. The species has heretofore been regarded as rare in Australian waters, and relatively uncommon elsewhere. Surface water temperatures during commercial fishing ranged from 12.0 to 14.0�C. Age estimations by otoliths suggested 4+ to 6+ years for lengths 69.0-91.0 cm. The length-weight relationship was W = 0.000004SL3.322. The tuna were feeding mainly on pelagic Crustacea. Gonad inspection showed that spawning had occurred recently. Three internal parasites (Anisakis sp., Copepoda, Cestoda) were found in 89.3, 95.7 and 61.7% of the 46 fish examined. Fish flesh was extremely oily (10-50%), and mercury analysis gave readings from 0.1 to 0.2 mg/kg.