The ovaries of 501 female eastern Atlantic bluefin tuna (Thunnus thynnus Linnaeus, 1758) captured in the Mediterranean Sea from May to September between 1998 and 2004 were analysed histologically. Body size at median sexual maturity (L-50) was 103.6 cm, fork length (FL), while 100% maturity was reached above 135 cm FL. The age analysis, based on the count of the translucent zones of the first spiniform ray of the first dorsal fin, showed that most of the specimens with FL = L-50 were 3 years old while 100% maturity was reached between 4 to 5 years. The reported evidence indicates that for the eastern Atlantic bluefin tuna stock, the size and age of first sexual maturity of females was lower than in the western Atlantic stock.\u

The histological analysis of eastern Atlantic bluefin tuna Thunnus thynnus ovaries caught from February to September 1999-2000, made it possible to distinguish the presence of seven oocyte developmental stages and allowed the characterization of six time-dependent ovary maturity stages. The ovaries of mature (fork length, L F ≥ 110 cm) bluefin tuna were non-active from August (spent period) to March (quiescent period) when they contained only perinucleolarstage oocytes. Ovary development started in April to early May (recrudescent period) with the appearance of oocytes at the lipid stage. Vitellogenesis appeared in mid-May (ripening period) and post-vitellogenesis occurred in late May to mid-June (pre-spawning period). In late June to early July, hydrated oocytes, a sign of imminent spawning, were found only in specimens caught in Balearic waters. Females ranging between 100 and 110 cm L F, captured during the recrudescent and ripening periods, had the largest oocytes at the lipid stage, most of which were degenerating. An extensive vitellogenic atresia was observed in the ovaries of five females caught during the spawning period in non-spawning areas

-Incidental catch or bycatch represents a significant threat for the conservation of seabird populations. The western Mediterranean is an important fishing area where the Spanish pelagic and semi-pelagic longline fleet targeting swordfish (Xiphias gladius), bluefin tuna (Thunnus thynnus) and albacore (Thunnus alalunga) operates. Bycatch of these fisheries includes several seabird species. Given the importance of conservation of the bycatch species (marine mammals, turtles, sharks and seabirds), an on-board observer program was implemented by the Spanish Oceanographic Institute (IEO); this included collecting data on effort and catch, as well as weight and number of individuals of the main bycatch species. The aim of the present study is to report data on seabird bycatch collected by the on-board observer program of the IEO in the Western Mediterranean. Data on seabird bycatch were collected for the period 2000-2008, throughout the year. Six longline gears targeting large pelagic fish were identified operating in the area of study, but only three had an effect on seabird species. Differences in catch per unit effort (CPUE, birds per 1000 hooks) for each gear, as well as their effect on particular seabird species, are reported in this study. A total of 4 786 466 hooks were monitored, which yielded 182 seabirds belonging to 7 different species. The average CPUE for the studied period was 0.038 birds per 1000 hooks. Cory's shearwater (Calonectris diomedea) and yellow-legged gull (Larus michahellis) were the species the most highly represented in the catch. In contrast, Balearic shearwater (Puffinus mauretanicus) was only present in the longline fishery targeting albacore (CPUE = 0.005 birds per 1000 hooks). Our results suggest that Cory's shearwater is the species the most affected by the longline fishery in the Western Mediterranean, probably due to its biological characteristics, and corroborate the well-established downward trend in its population.Key words: Bycatch / Seabird / CPUE / Western Mediterranean Sea / Pelagic longline Résumé -Les captures fortuites ou accessoires représentent une menace considérable pour la sauvegarde des populations d'oiseaux de mer. La partie occidentale de la Méditerranée est une zone importante de pêche où la flotte espagnole de palangriers pélagiques et semi-pélagiques opère et cible l'espadon (Xiphias gladius), le thon rouge (Thunnus thynnus) et le germon (Thunnus alalunga). Les captures accessoires de ces pêches incluent plusieurs espèces d'oiseaux de mer. Étant donnée l'importance de la protection des espèces capturées accidentellement (mammifères marins, tortues, requins et oiseaux de mer), un programme a été mis en place par l'Institut espagnol d'Océanographie (IEO) : des observateurs étant à bord collectent des données d'effort de pêche et de capture, aussi bien que le nombre d'individus et le poids des principales espèces des prises accessoires. L'objectif de cette étude est de rapporter les données de captures accessoires des oiseaux de mer, collectées par ce prog...

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Comparative histological and stereological analysis of gonads from longline-and purse seine-caught Atlantic bluefin tuna Thunnus thynnus was undertaken to assess the reproductive potential of the population in the western Mediterranean breeding area. Bluefin tuna sampled by purse seine clearly had higher gonadosomatic index values (GSI) than those caught by longline. While no remarkable histological differences were found between purse seine-and longline-caught males, the ovarian histology indicated a higher level of maturity in females from purse-seine samples, where most specimens were found to be in active spawning (AS). Within the longline sample the proportion of active spawning females was considerably higher at the end of the fishing season (midJune to mid-July) than earlier in May to mid-June (52.8 vs. 24%). Stereological analyses revealed that the samples collected by the 2 sampling gears differed primarily in the numbers of migratorynucleus oocytes, which were overwhelmingly more abundant in purse-seine catches, with average relative fecundity: 59 oocytes g -1 vs. 1.2 oocytes g -1 (purse-seine vs. longline). The frequency of ovaries with postovulatory follicles (POFs) in purse seine-caught bluefin tuna was 83.7%, equivalent to a spawning interval of 1.2 d; in contrast, only 32.6% of the females in longline catches had POFs, representing a spawning interval of 3.1 d. Assuming an average individual duration of the spawning process of 14 d, and considering the estimates of fecundity and spawning interval obtained from purse-seine samples, the average annual fecundity of bluefin tuna in the Balearic spawning ground would be approximately 77 × 10 6 eggs (relative fecundity of 702 eggs g -1 BW [body weight]).