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In the Gulf of Guinea, bigeye tuna (Thunnus obesus; BET) and yellowfin tuna (Thunnus albacares; YFT) are an important part of commercial fisheries and play a prominent ecological role as top predators. Using fatty acid profiles and carbon and nitrogen stable isotopes, we examined their trophic niche partitioning in this understudied region. Trophic niche overlap was high (>70%), similar to percentages in other ocean basins. BET occupied a higher trophic position than YFT and fed on deeper prey (high [delta][sup.15]N values and high proportions of monounsaturated fatty acids). The trophic position of YFT decreased slightly in the last 15 years ([delta][sup.15]N values decreased by ~0.5[per thousand]), suggesting a change in epipelagic communities, as observed in the eastern Pacific Ocean. Ontogenic changes were limited to BET. For both species, the dietary proportion of the diatom marker 20:5(n-3) increased in the seasonal upwelling area, highlighting the influence of seasonal habitat on the diet of tuna. The relatively lipid-rich muscle (~6% dry mass) of Atlantic tropical tuna suggests a richer diet in this region than that of Indian Ocean tropical tuna and (or) differences in energy allocation strategies.Dans le golfe de Gurnee, le thon obese (Thunnus obesus; BET) et le thon jaune (Thunnus albacares; YFT) sont importants pour les peches commerciales et jouent un role ecologique de premier plan comme predateurs de haut niveau trophique. En utilisant les profils d'acides gras et les isotopes du carbone et de l'azote, nous examinons la separation de niches trophiques dans cette region sous-etudiee. Le chevauchement de niche trophiques est eleve (>70 %), un pourcentage semblable a ce qui est observe dans d'autres bassins oceaniques. Le BET occupe une position trophique plus haute que le YFT et s'alimente de proies vivant plus en profondeur (valeurs plus elevees de [delta][sup.15]N et plus grandes proportions d'acides gras monoinsatures). La position trophique du YFT a legerement baisse au cours des 15 dernieres annees (baisse de ~0,5 [per thousand] des valeurs de [delta][sup.15]N), ce qui indiquerait une modification des communautes epipelagiques, a l'instar de ce qui est observe dans l'est de l'ocean Pacifique. Les changements ontogeniques se limitent au BET. Pour les deux especes, la proportion du regime alimentaire du marqueur de diatomees 20:5(n-3) augmente dans la zone de remontee d'eaux froides saisonniere, soulignant une influence saisonniere de l'habitat sur l'alimentation des thons. Les muscles relativement riches en lipides (~6 % en poids sec) des thons de l'Atlantique tropical indiqueraient un regime alimentaire plus riche dans cette region que celui des thons tropicaux de l'ocean Indien ou des differences sur le plan des strategies d'allocation d'energie. [Traduit par la Redaction], IntroductionBigeye tuna (Thunnus obesus; BET) and yellowfin tuna (Thunnus albacares; YFT) are oceanic predators co-occurring in tropical waters worldwide. In the eastern Atlantic Ocean, around 200 0001 of BET and [...]

The feeding strategy of female yellowfin tuna (Thunnus albacares) during their reproductive cycle was investigated using a combination of different trophic tracers, i.e., stomach contents and dual stable isotope analysis, along with an assessment of ovarian development based on a histological analysis. To complete these analyses, we collected 215 female yellowfin from the Western Indian Ocean in 2009 and 2010. From these fish, we noted the ovarian development and analyzed the contents of 166 non-empty stomachs and 104 liver and muscle tissue samples. Stomach content analysis identified a large variety of prey species (45 prey families), key groups including crustaceans dominated by the swimming crab Charybdis smithii and crustacean larvae; fish dominated by the cigarfish Cubiceps pauciradiatus; and cephalopods dominated by ommastrephids Sthenoteuthis oualaniensis and Ornithoteuthis volatilis. Individuals capable of spawning appeared to feed intensively, particularly on cigarfish, during the reproductive period. From the mean reconstituted weight values of the preys, our results indicated that this intensive feeding led to increased amounts of acquired energy. The results of the stable isotope analyses, carried out on the muscle and liver tissues, indicated a clear decrease in values from north to south. These analyses also showed that liver [delta].sup.15N values in spawning females were significantly lower than those in immature and developing individuals. This latter observation highlights the differences in metabolic processes that occur between tissues during ovarian development and underlines the importance of the liver in energy acquisition and mobilization in female yellowfin tuna during reproduction., Author(s): Iker Zudaire[sup.1] [sup.2] [sup.3], Hilario Murua[sup.2], Maitane Grande[sup.2], Nicolas Goñi[sup.2], Michel Potier[sup.3], Frederic Menard[sup.4], Emmanuel Chassot[sup.5], Nathalie Bodin[sup.5] Author Affiliations: (1) IKERBASQUE, Basque Foundation for Science, Maria Diaz de [...]

Abstract--The reproductive biology of Yellowfin Tuna (Thunnus albacares) in the western Indian Ocean was investigated from samples collected in 2009 and 2010. In our study, 1012 female Yellowfin Tuna were [...]

The reproductive biology of albacore tuna, Thunnus alalunga, in the western Indian Ocean was examined through analysis of the sex ratio, spawning season, length-at-maturity (L50), spawning frequency and fecundity. From 2013 to 2015, a total of 923 female and 867 male albacore were sampled. A bias in sex ratio was found in favor of females with fork length (LF) < 100 cm. Using histological analyses and gonadosomatic index, spawning was found to occur between 10°S and 30°S, mainly to the east of Madagascar from October to January. Large females contributed more to reproduction through their longer spawning period compared to small individuals. The L50 (mean ± standard error) of female albacore was estimated at 85.3 ± 0.7 cm LF. Albacore spawn on average every 2.2 days within the spawning region and spawning months, from November to January. Batch fecundity ranged between 0.26 and 2.09 million oocytes and the relative batch fecundity (mean ± standard deviation) was estimated at 53.4 ± 23.2 oocytes g-1 of somatic-gutted weight. The study provides new information on the reproductive development and classification of albacore in the western Indian Ocean. The reproductive parameters will reduce uncertainty in current stock assessment models which will eventually assist the fishery to be sustainable for future generations., Competing Interests: The authors have declared that no competing interests exist.