[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: 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abbreviated as L) of 2,458,028 Atlantic bluefin tuna, Thunnus thynnus (L.), taken from 224 scientific publications and unpublished L data from scientific organizations and fishing companiesspanning most of the known Atlantic and Mediterranean Atlantic bluefin tuna fisheries dating from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.
[Show abstract][Hide abstract] ABSTRACT: The western Mediterranean is an important fishing area in which the Spanish longline fleet operates. Longline fisheries affect several species of marine mammals, sea turtles, sharks and seabirds, all of which are especially sensitive to fishing mortality. Given international efforts to identify and reduce the bycatch of sensitive species, an onboard observer program was implemented by the Spanish Oceanographic Institute (IEO, Instituto Español de Oceanografía). The aim of the present study was to report data on marine mammal bycatch in the western Mediterranean. The additional aim was to improve knowledge about the possible effects of the Spanish longline fisheries on cetacean populations, particularly Risso's dolphin, and to suggest improvements to fisheries management. Data on marine mammal bycatch were collected during the period 2000-2009. Differences are reported for catch per unit effort (CPUE, defined as marine mammals per 1000 hooks) for each type of gear (n = 7), as well as their effect on specific marine mammal species. A total of 5 398 297 hooks were monitored, which yielded 56 marine mammals belonging to 4 different species. Our results indicate that Risso's dolphin is the species most affected by the longline fishery in the western Mediterranean (n = 33). We built a predictive model for Risso's dolphin bycatch using variables associated with the technical characteristics of the fishery, geographic location and seasonality. We performed a binary logistic regression of the presence/absence of Risso's dolphin bycatch to test whether the probability of incidentally catching one or more dolphins may be predicted by some of the explanatory variables selected. Our results indicate that Risso's dolphin was mainly caught using Japanese longline (LLJAP) or an experimental home-based longline (LLHBexp) over the continental shelf. Because LLHBexp is an experimental type of gear that was only used occasionally by the fleet, controlling the use of LLJAP over the continental shelf could strongly reduce the impact of these fisheries on populations of Risso's dolphin in the western Mediterranean.
Aquatic Living Resources 10/2012; 25(4):321-331. DOI:10.1051/alr/2012038 · 1.01 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. DOI:10.1017/S002531541000069X · 1.06 Impact Factor
[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: 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.
Aquatic Living Resources 10/2010; 23(4). DOI:10.1051/alr/2010022 · 1.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Semi-enclosed and bounded by three continents, the Mediterranean sea is a region highly vulnerable to
human activities, i.e.: the population surge along the coasts, the tourism pressure, the maritime traffic, the
agriculture and the fishery exploitation, all have a potential impact on the Mediterranean environment.
In addition, effective initiatives against the Global Climate Change need to be attempted in order to
preserve our marine environment and to achieve a sustainable development of its resources. Prevention
and adaptation to this new threat must be based on the rigorous and scientific knowledge accomplished
through the systematic and continuous observation of the sea, and through the collection of
multidisciplinary time-series and the subsequent analysis.
This report responds to this necessity. The main goals of the Instituto Español de Oceanografía (IEO) are to
generate scientific knowledge, as well as to assess and to inform the public about the state of the sea. The
IEO is primary focussed on the study of the variety of phenomena influencing spanish coasts, including the
process of Climate Change.
To meet these objectives, a large set of actions have been planned. Some of them are already being
implemented, such as a multidisciplinary observation system in the shelf and continental slope waters, or
periodic scientific reports dealing with the detection and quantification of Climate Change effects and of
other possible environmental impacts. The present report is the first of a series of future contributions.
Besides the IEO, other Spanish institutions such as the ICM (CSIC), Puertos del Estado (PE), the IMEDEA
(CSIC), the UMA, the UIB and the INM, involved in the monitoring, analysis and modelling of the
Mediterranean sea, have also participated in it. The results show clear evidences of the effect of Climate
Change in the physical properties of the mediterranean waters since 1948; in particular, the temperature
and salinity increase of the deep waters, the accelerated rise of sea level since the early 1990s, and the air
and sea surface temperature increase during the second half of the XX century.
Temas de Oceanografía, 2 01/2009; Instituto Español de Oceanografía., ISBN: 84 95877 39 2
[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: 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.
[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 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