[Show abstract][Hide abstract] ABSTRACT: A meta-analysis of the straight fork lengths (herewith abbreviated as L) of 2,458,028 Atlantic bluefin tuna, Thunnus thynnus (L.), taken from 224 scientific publications and unpublished L data from scientific organizations and fishing companiesspanning most of the known Atlantic and Mediterranean Atlantic bluefin tuna fisheries dating from 1605 to 2011, give L values ranging from Lmin = 20 cm and Lmax = 330 cm. The results indicate that the parameter L∞ = 318.85 cm of the growth equation used by ICCAT’s Standing Committee on Research and Statistics Atlantic bluefin tuna assessment group for the eastern stock (Lt = 318.85 [1 – e−0.093 (t + 0.97)]) lies within the confidence limits of the maximum Ls presented in the
study: Lmax = 319.93 ± 11.3 cm, confirming that this equation perfectly fits the biology of the growth of this species. Theseconclusions are also valid for the equation for the western stock (Lt = 314.90 [1 – e−0.089 (t +1.13)]). The ICCAT Atlantic bluefin tuna database contains numerous records of Atlantic bluefin tuna L outside the biological feasibility, and solutions are provided to recognize and remove these outliers based on the application of fixed values of Fulton’s condition factor (K) between 1.4 and 2.6 and appropriate L-W relationships to correct this situation in the future.
Reviews in Fisheries Science 06/2013; 21(2):181-212. · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: On the one hand, a recent study on sea turtle by-catch during surface longline fishing targeting swordfish in the western Mediterranean Sea showed that sea turtle by-catch is independent of fishing effort and other technological factors. When the distance to the coast increases, there is a higher probability of catching a loggerhead turtle. The authors proposed to avoid fisheries further than 35 nautical miles (approximately 65 km) from the coast. However, the proposed 35 nautical miles limit could be useful where the continental shelf is narrow, as in the Balearic Sea, and useless where it widens. On the other hand, ecological model validation is considered essential for management application. The objective of the present paper is to validate the new fisheries loggerhead by-catch model in different areas outside the Balearic Sea with wider continental shelves, aimed at maintaining sustainable fishing activity compatible with the conservation of the loggerhead populations. Our present results validate the previous model, and stress the importance of the eco-geographical variable distance to the coast in understanding the loggerhead by-catch (or incidental capture) per unit effort for the longline fisheries targeting swordfish.
Journal of the Marine Biological Association of the UK 08/2011; 91(06):1381 - 1383. · 1.02 Impact Factor
[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: 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: 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: Drifting longline is considered one of the most dangerous fishing gears for marine tur- tles and is their principal threat in the western Mediterranean Sea. During the summers of 2000 to 2003, 179 fishing operations were observed onboard a traditional Spanish drifting longline boat in the Balearic Sea (western Mediterranean) to analyse the effects of fishing effort and ecogeographical fac- tors on the by-catch of loggerhead turtles Caretta caretta. We observed 4074 swordfish captured and 675 loggerhead turtles by-caught. The probability of catching at least 1 loggerhead was related to the distance of the fishing-ground to the coast and, to a lesser extent, depth, both independent of fishing effort. The average number of loggerheads captured was spatially structured only according to mean distance to the coast. However, the number of swordfish captured was correlated with fishing effort but was not correlated with distance to the coast or depth. Distance to the coast was correlated with gear retrieval time, sea surface temperature and velocity, and phytoplankton concentration. As the number of loggerheads captured was independent of the number of hooks, the number of fishing operations was a better unit than the number of hooks to assess loggerhead by-catch. Limiting drift- ing longline fishing activity to within 35 international nautical miles from the coast could reduce log- gerhead by-catch substantially without affecting swordfish captures and with little resistance from fishermen.
Marine Ecology-progress Series - MAR ECOL-PROGR SER. 01/2007; 338:249-256.
[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: 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: 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). firstname.lastname@example.org 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: 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: 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: SUMMARY A total of 70 Gonads of Swordfish, Xiphias gladius, were collected from two areas of the South Western Mediterranean along 2003 (June to October): a Spanish area located near to Aguilas (Murcia) and a coastal Tunisian area near to Zarzis and Kélibia. These gonads were examined in order to determine maturity and other reproductive characteristics (Sex-ratio, oocyte developmental features, etc) of this species. The fishes collected ranging from 85 cm to 178 cm in low jaw-fork length (LJFL) in the Tunisian sample and from 1060 mm to 2140 mm in the Spanish one. The sex-ratio was 3:1 F/M in the Tunisian sample and 2.25:1 in the Spanish one. All female fishes over 160 cm was sexually mature. The first maturity (50%) occurs from 130 to 160 cm in this area. Female low 130 cm LJFL was all sexually inmature. The males are very scarce in the sample so we cannot discuss about male first maturity size in this paper. The microscopic appearance of the oocytes and the oocyte size frequency distribution had been used to define the spawning pattern shown by these species. These and other reproductive aspects (reproductive areas and seasons, etc) will be discussed in this paper. The aim of this paper is to increase our knowledge about sexual maturity, reproductive season and spawning area of swordfish of the South Western Mediterranean (Tunisia and Spain) as an important tool for determining a correct policy for the management of fish stock. RÉSUMÉ
[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
[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.