[Show abstract][Hide abstract] ABSTRACT: Relative abundance indices of bluefin tuna (Thunnus thynnus) caught by the Moroccan and Spanish traps in the area close to the Strait of Gibraltar were estimated for the period 1981-2013. Standardized CPUEs were estimated through a General Linear Modeling (GLM) approach under a negative binomial error distribution assumption.
[Show abstract][Hide abstract] ABSTRACT: Standardized CPUEs were estimated through a General Linear Modeling (GLM) approach under a negative binomial error distribution assumption. RÉSUMÉ Des indices d'abondance relative de thon rouge (Thunnus thynnus) capturé par des madragues espagnoles et marocaines dans la zone proche du détroit de Gibraltar ont été estimés pour la période allant de 1981 à 2009. Des CPUE standardisées ont été estimées par le biais d'une approche de modélisation linéaire généralisée (GLM) en postulant une distribution d'erreur binomiale négative. RESUMEN Se estimaron, para el periodo 1981-2009, índices de abundancia relativa de atún rojo (Thunnus thynnus) capturado por almadrabas españolas y marroquíes en el área cercana al Estrecho de Gibraltar. Las CPUE estandarizadas se estimaron mediante un enfoque GLM con un supuesto de distribución de error binomial negativa.
ICCAT-GBYP Symposium on Trap Fisheries for Bluefin Tuna; 01/2011
[Show abstract][Hide abstract] ABSTRACT: SUMMARY In year 2006 the Spanish Institute of Oceanography carried out the swordfish tagging activities scheduled by the European Tagging Programme. A total of 260 swordfish, which size (LJFL) ranged between 45 and 124 cm, were tagged by means of conventional tags. Several hooks, including circular ones, were used during tagging activities; as a result 79% of the swordfish was hooked on the mouth, which is supposed to favour fish survival. This document reports information on the first tag from a swordfish released in the Mediterranean Sa and recaptured in the Atlantic RÉSUMÉ
[Show abstract][Hide abstract] ABSTRACT: 2 SUMMARY A total of 755 anal fins from western Mediterranean swordfish were analyzed from 2003 to 2005 for ageing and growth studies. The lower jaw fork lengths of the aged individuals ranged from 54 to 186 cm for the males and from 55 to 223 cm for the females. Fish ages ranged 0 to 10 years old and the mean lengths by age were calculated for males and females. Growth parameter estimates were calculated from 720 cut spine sections which provided readable growth annuli by sex. The standard von Bertalanffy growth function and two versions of the generalized model (Richards' and Chapman's) were used to fit length at- age data.The growth parameters based on standard VB growth function are the following: for males, L∞ (asymptotic length)=185.5 cm, k (growth coefficient)=0.219 , t0 (age at zero length)=-1.968; for females, L∞=263.5 cm, k=0.119 , t0=-2.27. The relationships between LJFL and anal fin spine radius were calculated for both sexes. The trens in the monthly marginal increment ratio was not conclusive regarding growth bands formation along the year. RÉSUMÉ
[Show abstract][Hide abstract] ABSTRACT: ICCAT considers the North Atlantic and the Mediterranean swordfish populations as two
separate fish stocks and consequently recommends independent management actions for these
two regions. Genetic analyses realized to date have confirmed genetic differentiation between
these two areas, with a plausible population substructure within the Mediterranean Sea. All
these studies agree to establish the Strait of Gibraltar as the principal region to prevent gene
flow between the North Atlantic and the Mediterranean. However, the present analysis realized
with mitochondrial DNA sequence variation of new Atlantic samples together with
Mediterranean swordfish showed that the phylogeographic signal, distinctive of the
Mediterranean population, is also identified in a reduced part of the northeast Atlantic limited
about 10º West. Surprisingly, in this area the phylogeographic signal of North Atlantic
swordfish can also be recognized. Although extended sampling, with special focus on adjacent
regions, is necessary to fully confirm this hypothesis, the results of the present genetic study
indicate that the Mediterranean populations limit exceed the Strait of Gibraltar enclosing this
northeast Atlantic region where a mixed stock can be found.
Proceedings of the Atlantic swordfish population structure workshop. ICCAT Col. Vol. Sci. Pap.; 01/2007
[Show abstract][Hide abstract] ABSTRACT: The aim of this paper is to estimate the approximate number of fish that would need to be tagged in an experiment with the objective of estimating movement rates of east Atlantic bluefin tuna. For that purpose different tag-recapture scenarios were simulated and fitted using spatially structured tag attrition models. In order to work with realistic scenarios, real data available was previously analyzed using the same type of models. Migration to and from the western Atlantic was also considered in order to work with a closed system. Transatlantic migration rate estimates using real data were similar to previous studies, while migration rates between the eastern Atlantic and the Mediterranean ranged considerably depending on the model definition and reporting rate assumptions. Under most of the proposed assumptions, practically no gain in precision and accuracy occurred when tagging more than 10,000-15,000 fish in total that could be distributed in a single or two consecutive years .However, some parameters would still be estimated with important relative standard error. The importance of knowing the reporting rate is stressed. RÉSUMÉ Le but du présent document est d'estimer le nombre approximatif de poissons nécessitant être marqués dans une expérimentation visant à estimer les taux de déplacement du thon rouge de l'Atlantique Est. A cette fin, divers scénarios de marquage/récupération de marques ont été simulés et ajustés en utilisant des modèles d'attrition de marques spatialement structurés. Afin de travailler avec des scénarios réalistes, les données réelles disponibles ont été auparavant analysées à l'aide des mêmes types de modèles. La migration à destination et en provenance de l'Atlantique Ouest a également été examinée afin de travailler en système clos. Les estimations des taux de migration transatlantique employant des données réelles se sont avérées similaires aux études antérieures, tandis que les taux de migration entre l'Atlantique Est et la Méditerranée ont considérablement fluctué en fonction de la définition des modèles et des taux de déclaration postulés. Dans la plupart des postulats proposés, le marquage de plus de 10.000-15.000 poissons au total qui pouvaient être répartis en l'espace d'une ou deux années consécutives n'a entraîné pratiquement aucun gain en précision ou en exactitude. Toutefois, certains paramètres seraient encore estimés avec une importante erreur relative standardisée. Les auteurs soulignent l'importance de connaître le taux de déclaration. RESUMEN El objetivo de este documento es estimar el número aproximado de peces que sería necesario marcar en un experimento para estimar las tasas de movimiento del atún rojo del Atlántico este. Con este fin, se simularon y ajustaron diferentes escenarios de marcado-recaptura utilizando modelos basados en pérdidas de marcas espacialmente estructurados. Para trabajar con escenarios realistas, se analizaron previamente los datos reales disponibles utilizando el mismo tipo de modelos. Para trabajar con un sistema cerrado se consideró también la migración hacia y desde el Atlántico oeste. Las estimaciones de la tasa de migración transatlántica que utilizaban datos reales eran similares a los estudios previos, mientras que las tasas de migración entre el Atlántico este y el Mediterráneo oscilaron considerablemente 1 AZTI. Herrera Kaia Portualdea z/g. 20110 Pasaia. Basque Country (Spain). email@example.com 2 IEO. Puerto Pesquero s/n. Apdo 285,29640 Fuengirola (Málaga) 770 dependiendo de la definición del modelo y de los supuestos de la tasa de comunicación. Bajo la mayoría de los supuestos propuestos, el marcado de más de 10.000-15.000 peces en total que pudieran distribuirse en un año o dos años consecutivos no produjo prácticamente ninguna ganancia en precisión y exactitud. No obstante, algunos parámetros se estimarían con un importante error estándar relativo. Se resalta la importancia de conocer la tasa de comunicación. KEYWORDS Thunnus thynnus, conventional tagging, migration rates, tag attrition models, experimental design.
[Show abstract][Hide abstract] ABSTRACT: The Atlantic bluefin tuna (BFT; �Thunnus thynnus�) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. The BFT population appears to be divided into a western and an eastern stock, which spawn, respectively, in the Gulf of Mexico and the Mediterranean Sea. To extend our understanding of the reproductive activity of the eastern BFT stock, we tracked gonadal development in wild fish that were temporally sampled across the Mediterranean Sea. In parallel, we assessed reproductive potential of captive BFT captured at the Balearic Islands and held in floating cages on the coast of Murcia. Wild BFT were sampled from early May throughout July during three consecutive years (2003 - 2005) by means of traditional fishery methods (i.e., labyrinth net, purse seine, or longlines). Sampling locations across the Mediterranean Sea included the Levantine Sea, Malta, strait of Messina, Sardinia channel, and the Balearic Islands. An additional sampling point, Barbate (Spain), was situated to
[Show abstract][Hide abstract] ABSTRACT: SUMMARY This paper presents data on the by-catch species landed by the Spanish surface longline fleet targeting swordfish (Xiphias gladius) in the Atlantic Ocean and preliminary data of Mediterranean, between 2000 and 2004. The species assumed as by-catches amounted to 75.3% of the total landings in weight from the Atlantic areas, large pelagic sharks to 70.3%, tunas to 3.2, billfish to 1.1%, and other species to 0.6%. As far as by-catch species are concerned, large pelagic sharks were the most prevalent ones with an average of 93.2% of the catch in weight, whereas tunas amounted to 4.3%, billfish to 1.6% and other species to 0.9%. The three most prevalent species in the catch, Xiphias gladius, Prionace glauca and Isurus oxyrhinchus, represented, on average, 92.8% of the total landings in weight during this period. Prionace glauca and Isurus oxyrhinchus are the most prevalent species within the group of large pelagic sharks, reaching prevalences of 86.3% and 10.5%, respectively, which is very similar to levels observed in other oceans. RÉSUMÉ
[Show abstract][Hide abstract] ABSTRACT: SUMMARY Bullet tuna (Auxis rochei) is one of the most abundant small tuna species in the Mediterranean Sea. This species is commercially exploited in the Spanish coast by traditional fisheries. Nevertheless, the biological and reproductive information about this species is currently scarce in the Western Mediterranean. Sex-ratio, maturity, oocyte developmental features, spawning areas and other reproductive characteristics of this population have already been described by the authors in previous papers. In order to improve our knowledge about the reproductive parameters, specifically, the fecundity of this population, gonads were collected during June 2003 in a Spanish Mediterranean trap (La Azohía, Murcia). The fish collected ranges from 334 to 470 mm in fork length. All these fish were mature and their reproductive characteristics indicate a spawning area near to the trap location. Batch fecundity was estimated using just pre-spawning females without postovulatory follicles in their ovaries. The average fecundity was 233941 oocytes by spawning batch. The relative batch fecundity, a parameter particularly useful to compare females of different size classes, ranges from 150 to 365 oocytes g-1, with an average value of 242 oocytes g-1. Histological and stereological methods allow the obtaining of adequate estimates of fecundity in this species. RÉSUMÉ
[Show abstract][Hide abstract] ABSTRACT: The Atlantic bluefin tuna (BFT; Thunnus thynnus) is a migrating species straddling the North Atlantic Ocean and Mediterranean Sea. It is assumed that BFT is divided into two populations: a western and an eastern stocks, which spawn, respectively, in the Gulf of Mexico (during April to June) and in the Mediterranean Sea (during June to August). To extend our understanding of the reproductive activity of the eastern BFT stock, we tracked gonadal development in adult fish that were temporally and spatially sampled across the Mediterranean Sea. Samplings by means of traditional fishery methods (i.e., labyrinth net, purse seine, or longlines) were carried out from early May throughout July, during three consecutive years (2003 - 2005). Sampling locations across the Mediterranean Sea included the Levantine Sea, Malta, strait of Messina, Sardinia channel, Pt. de Mazarron and the Balearic Islands. An additional sampling point, Barbate (Spain), was situated to the northwest of the strait of Gibraltar, through w
[Show abstract][Hide abstract] ABSTRACT: Cytochrome P4501A (CYP1A) monoxygenase, vitellogenin (Vtg) and Zona radiata proteins (Zrp) are frequently used as biomarkers of fish exposure to organic contaminants. In this work, swordfish liver sections obtained from the Mediterranean Sea, the South African coasts (South Atlantic and South Western Indian Oceans) and the Central North Pacific Ocean were immunostained with antisera against CYP1A, Zrp, and Vtg. CYP1A induction was found in hepatocytes, epithelium of the biliary ductus and the endothelium of large blood vessels of fish from the Mediterranean Sea and South African waters, but not from the Pacific Ocean. Zrp and Vtg were immunolocalized in hepatocytes of male swordfish from the Mediterranean Sea and from South African waters. Plasma Dot-Blot analysis, performed in Mediterranean and Pacific specimens, revealed the presence of Zrp and Vtg in males from Mediterranean but not from Pacific. These results confirm previous findings about the potential exposure of Mediterranean swordfish to endocrine, disrupting chemicals and raise questions concerning the possible presence of xenobiotic contaminants off the Southern coasts of South Africa in both the South Atlantic and South Western Indian Oceans.
[Show abstract][Hide abstract] ABSTRACT: Preliminary results of tuna larval surveys conducted off different Mediterranean regions during the
2004 bluefin spawning season are presented. Data on bluefin and other tuna species larval catches are
reported from the Balearic Sea, the Levantine Sea and the Sicilian coasts. The Balearic Sea showed the
highest bluefin larval catch which are clearly associated to surface temperatures within the range of
24-25ºC. The Levantine Sea survey caught significant bluefin larval catches over the southern Turkish
coasts. The Sicilian survey showed lowest catches, possibly due to a lower bluefin spawning activity
caused by a lower surface temperature regime during the survey. The similarities in the hydrographic
patterns with the Balearic Sea are discussed.
[Show abstract][Hide abstract] ABSTRACT: The Bluefin Year Program (BYP) is a special research program funded by ICCAT aimed at
improving the understanding of the population dynamics of Atlantic bluefin tuna. Part of the
program is devoted to supporting larval surveys in the two known spawning grounds, the Gulf
of Mexico and the Mediterranean Sea. This document reports on a meeting held to coordinate
the work of researchers interested in conducting larval surveys and studies of reproductive
biology for bluefin tuna in the Mediterranean.
[Show abstract][Hide abstract] ABSTRACT: SUMMARY The bullet tuna (Auxis rochei) is one of the most abundant small tuna species in the Mediterranean Sea. This species is commercially exploited in the Spanish coast by traditional fisheries. Nevertheless, the biological and reproductive information about this species is currently scarce in the Western Mediterranean. Gonads of Bullet tuna from a Spanish Mediterranean trap (la Azohia, Murcia) were collect along June (2003) in order to determine the reproductive characteristics (Sex-ratio, maturity, oocyte developmental features, etc) of the population. The fish collected ranging from 334 to 470 mm in fork length. The sex-ratio was 1:1.7 F/M. All these fishes were mature and their reproductive characteristics indicate a spawning area near to the trap location. These and other biological aspects (size distribution, size/weight relations, etc) will be discussed in this paper. RÉSUMÉ