SCRS/2009/128 Collect. Vol. Sci. Pap. ICCAT, 65(3): 755-769 (2010)

755

ON-GOING BLUEFIN TUNA RESEARCH IN THE BAY OF BISCAY (NORTHEAST ATLANTIC):

THE “HEGALABUR 2009” PROJECT

Nicolas Goñi1, Igaratza Fraile1, Igor Arregui1, Josu Santiago2, Guillermo Boyra1, Xabier Irigoien1, Molly Lutcavage3, Ben Galuardi3, John Logan3, Andone Estonba4,

Iker Zudaire1, Maitane Grande1, Hilario Murua1, Haritz Arrizabalaga1

SUMMARY

Little research has been focused to date on the juvenile fraction of Atlantic bluefin tuna (Thunnus thynnus, BFT) populations. For instance, although the baitboat CPUE from the Bay of Biscay is used as the only recruitment index for the eastern stock, little is known about the role of this juvenile feeding area within the life cycle of bluefin tuna. This, together with recent changes in the bluefin tuna management context, might jeopardize the usefulness of the CPUE-derived index. One objective of the ongoing “Hegalabur 2009” project is to analyze the possibility of using acoustic technologies (long-range sonar and ecoshounder) to get abundance indices of bluefin tuna in the Bay of Biscay. On the other hand, the project aims to understand the role of the Bay of Biscay in the life cycle of BFT, by identifying the origin of the bluefin tuna present in the Bay of Biscay, and the variability of the proportion of individuals of different origins. Acoustic surveys (scientific echosounders and commercial sonars), biological sampling and tagging (conventional and electronic) have been conducted. Some posibilities for developing acoustic indices of abundance are discussed, as well as the perspectives for different analyses (genetics, otolith microchemistry, reproduction, tagging).

RÉSUMÉ

Peu de recherches ont été menées à ce jour sur les juvéniles de thon rouge de l’Atlantique (Thunnus thynnus, BFT). Par exemple, bien que la CPUE de la pêcherie de canneurs du Golfe de Gascogne soit utilisée en tant qu’unique indice de recrutement pour le stock de l’Est, les connaissances sont lacunaires sur le rôle, au sein du cycle vital du thon rouge, de cette zone d’alimentation des juvéniles. Ces incertitudes, dans un contexte de récents changements dans la gestion de la pêcherie du thon rouge, pourraient compromettre l’utilité de la CPUE en tant qu’indice basé sur la CPUE. Un des objectifs du projet « Hegalabur 2009 » en cours à cette date est d’analyser la possibilité d’utiliser des technologies acoustiques (sonar longue portée et échosondeur) pour obtenir des indices d’abondance de thon rouge dans le Golfe de Gascogne indépendants de la CPUE. D’autre part, ce projet vise à comprendre le rôle joué par le Golfe de Gascogne dans le cycle vital du thon rouge, en identifiant l’origine des spécimens présents dans cette zone, et la variabilité de la proportion de spécimens de différentes origines. Des campagnes acoustiques (mettant en œuvre des échosondeurs scientifiques et des sonars commerciaux), des échantillonnages biologiques et des opérations de marquage (conventionnel et électronique) ont été menées à cet effet. Les possibilités de développement d’indices d’abondance acoustiques sont discutées dans le présent document, ainsi que les perspectives pour différents types d’analyses (génétiques, microchimie des otolithes, reproduction, marquage).

1 AZTI Tecnalia. Herrera Kaia Portualdea z/g. 20110 Pasaia (Gipuzkoa). Spain. Corresponding author: ngoni@azti.es 2 AZTI Tecnalia. Txatxarramendi Ugartea z/g. Sukarrieta, Bizkaia, Spain. 3 Large Pelagics Research Center. Department of Biological Sciences. University of New Hampshire. Durham, New Hampshire 03824 USA. 4 Antropologia Fisikoa eta Animalien Fisiologia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU), PO Box 48080, Bilbao, Spain.

756

RESUMEN

Se han realizado pocos estudios sobre los juveniles de atún rojo del Atlántico (Thunnus thynnus, BFT). Por ejemplo, a pesar de que la CPUE de la pesquería de cebo vivo del Golfo de Vizcaya es el único índice de reclutamiento que se usa para la evaluación del stock Este, se sabe poco del papel que desempeña esa zona de alimentación de juveniles dentro del ciclo vital del atún rojo. Las incertidumbres que existen al respecto, en un contexto de cambios recientes en la gestión de la pesquería, podrían poner en duda la relevancia de la CPUE como índice de abundancia. Uno de los objetivos del proyecto “Hegalabur 2009” es analizar la posibilidad de usar tecnologías acústicas (sonar de largo alcance y ecosonda) para obtener índices de abundancia de atún rojo en el Golfo de Vizcaya independientes de la CPUE. Por otro lado, el proyecto tiene como objetivo conocer el papel que juega el Golfo de Vizcaya en el ciclo vital del atún rojo, identificando el origen de los individuos presentes en el Golfo de Vizcaya, y la variabilidad de la proporción de individuos de diferentes orígenes. Para ello se han llevado a cabo campañas acústicas (ecosondas científicas y sonares comerciales), muestreos biológicos y marcado (convencional y electrónico) de los atunes. En este documento, se analizan las posibilidades de desarrollar índices de abundancia basados en datos acústicos, así como perspectivas para diferentes tipos de análisis (genética, microquímica de otolitos, reproducción, marcado).

KEYWORDS

Atlantic, bluefin tuna, Bay of Biscay, acoustics, tagging, genetics, reproduction

1. Introduction Atlantic bluefin tuna (BFT, Thunnus thynnus), the largest known teleost fish, is a highly migratory species of great economic interest. It has been exploited in the Mediterranean Sea and East Atlantic for several centuries, and is currently exploited in these zones as well as in the West Atlantic (Fromentin and Powers, 2005). During the last decades, the globally increasing fishing capacities, together with the important development of the sashimi market in Japan, contributed to a situation of overfishing and risk of collapse (Anon. 2009). Moreover, management advice has been characterized by large uncertainties in the general knowledge about bluefin tuna populations. This promoted the development of a large-scale Bluefin tuna Research Program (Anon., 2004; Anon. 2006) in order to try to improve future management advice. To date, most research on BFT has been conducted in the western Atlantic ocean (including the Gulf of México), and the Mediterranean Sea (Rooker et al., 2007). This is partly because the Gulf of México and the Mediterranean Sea are known spawning areas with important fisheries (especially in the Mediterranean). Regarding bluefin tuna in the open Atlantic ocean, some research has been conducted with concern to population structure and mixing between the two populations (Lutcavage et al., 1999; Block et al., 2005; Carlsson et al., 2006). Furthermore, the role of bluefin tuna in different oceanic areas has been investigated as fisheries have emerged and/or collapsed in those areas both in the past (off Norway and Brazil, Fromentin and Powers, 2005; Fromentin, 2009) and more recently (off Iceland, Carlsson et al., 2006). In terms of life stages, due to a large proportion of adults in the catches of important fisheries (e.g. purse seine, longline, traps), and/or due to more suitable technologies (e.g. pop-up tags) for large individuals, most research has been concentrated in the adult portion of the populations. As a consequence, the dynamics of the juvenile portion constitutes one of the main knowledge holes in the life cycle of BFT, as pointed out in the “Workshop on Juvenile Atlantic Bluefin Tuna: New Approaches for Assessment” (University of New Hampshire, March 21-22, 2005). In the Bay of Biscay (NE Atlantic), bluefin tuna has been mainly caught by baitboats since the 1950s, with average annual catch around 1500 t. The fishery occurs from May to October, during the BFT feeding migration to the Bay of Biscay, and is based mostly on juveniles (ages 2 and 3), although much older fish (up to age 9) are also caught. This fleet has collaborated with scientists in providing fishery statistics, including logbooks. Using this information, a CPUE series has been standardized and used as the only recruitment index available for the eastern stock (Rodriguez-Marin et al., 2003).

757

However, important uncertainties about the role of the Bay of Biscay feeding area on the life cycle of BFT still remain unresolved. For instance, it is neither known whether this feeding area is visited by a significant fraction of the stock or not, nor whether the fraction of the stock visiting the Bay of Biscay in summer is constant over time or presents interannual variations, which would limit the validity of the CPUE index as recruitment index. Moreover, in the open Atlantic area, a mix of individuals originating from the Mediterranean spawning sites and from the Gulf of Mexico spawning sites coexists, as shown through tagging experiments (Block et al., 2005). In this scenario, the relationship between the fish in the Bay of Biscay and those in the western Atlantic (Rooker et al. 2007) and the Mediterranean (Rodriguez-Roda, 1969; Cort and de la Serna, 1994; de la Serna et al., 2001; Rodríguez-Marín et al., 2005) has been evidenced by conventional tag recaptures. However, the proportion of Bay of Biscay BFT belonging to each of the nursery grounds is yet unknown, and also is unknown whether these proportions are constant over months, years and age groups. On top of this, recent management actions have affected the behavior of the fleet. Basque baitboats implemented the BFT recovery plan before it became mandatory in 2007. This has modified the definition of the commercial categories used to land and market fish. In addition, they have adopted specific harvesting strategies to try to get as much economic profit of their quota as possible. Given that their quota is now well below their average yearly catch, both in 2008 and 2009 they agreed to limit the maximum catch of BFT per boat, commercial category and week. The intention was to concentrate on harvesting as many adults as possible and to spread the catch along the fishing season to keep relatively high prices for all their catch. These changes are a handicap for the CPUE index to be used as recruitment index, as further standardization effort might be required in order to disentangle fleet behavior effects from year effects. Moreover, baitboat CPUE indices might present biases related to the interaction between the feeding behaviour of tunas and the use of live bait (Stoner, 2004). In such a context, the interest of alternative abundance indices, as well as of the origin and mixing of BFT in the Bay of Biscay is granted. The “Hegalabur 2009” project was designed according to these different issues, and was conducted for first time in the Bay of Biscay during summer 2009. 2. Objectives of the project On one hand, the project “Hegalabur 2009” aims to analyze the feasibility of acoustic technologies (sonar and ecoshounder) to get abundance indices of BFT in the Bay of Biscay, and compare acoustic estimates with CPUE based estimates. On the other hand, the project aims to understand the role of the Bay of Biscay in the life cycle of Atlantic bluefin tuna by identifying the origin (nursery ground) of the BFT present in the Bay of Biscay, and the variability – over time and among size-groups – of the proportion of individuals of different origins. These objectives were set and prioritized considering the Bluefin Tuna Research Program, and after discussions with scientists including SCRS participants. 3. Material and methods The “Hegalabur 2009” project has been conducted during the whole bluefin fishing season in the Bay of Biscay, from June 15th to October 15th, onboard a baitboat (FV Berriz Gure Naia) targeting bluefin tuna. During that period, the boat also targetted albacore tuna, depending on resource availability and on the status of the weekly bluefin tuna quota. The boat, although scientifically equipped and with scientists onboard, operated a normal fishing activity. The scientific work is divided into 3 tasks: 3.1 Acoustic observation

Baitboats use long range sonars as the main way to detect tuna schools. Sonar screenshots (Figure 1) are recorded during the whole BFT fishing period, every second. Image analysis of the screenshots, besides counting the number of BFT school detections, will allow, in the future, quantifying the signals to get an abundance index. In parallel, tuna catches on all fishing operations are recorded to allow comparison between sonar detections and tuna catches. This task is completed not only in the FV Berriz Gure Naia, but also in two other baitboats,

758

throughout the season. Besides this, empirical skipper estimates of the biomass detected by the sonar are recorded in the FV Berriz Gure Naia. Moreover, a Simrad EK60 scientific echosounder (Figure 2) working at three frequencies (38, 120 and 200 kHz) was installed on the FV Berriz Gure Naia and operated during late June, July and October. The 200 kHz transducer was installed horizontally in order to detect the fish aside the starboard of the vessel. The two other transducers, installed vertically, detected the fish under the boat. Local BFT abundances detected by the echosounder were compared with catches and sonar detections, and will further be estimated through the echointegration of the recorded data. 3.2 Biological sampling

Biological samples were taken from commercial fish during the whole fishing season. The sampling was stratified by periods of 15 days and by weight categories. From each individual, the following samples were taken, according to the different analyses to be conducted: − Otoliths for identification of the nursery ground (origin) and mixing, by mean of microchemical

analyses. Otoliths will also be used together with dorsal fin spines to determine the age of the individuals.

− Muscle, liver, heart and gill biopsy to study population structure, using genetic analyses.

− Muscle and liver for feeding ecology studies using stable isotope analyses

− Stomachs for feeding ecology studies through diet analyses

− Gonads of female individuals over 15 kg for reproductive studies and fecundity estimations using histological and image analyses

Besides onboard sampling, and following Resolution [08-06], fish manufacturers were contacted for access to fish being processed. Moreover, sport fishermen were also contacted to get samples of age 0 individuals from the Mediterranean Sea. 3.3 Tagging

Tagging activities were designed between AZTI Tecnalia and the University of New Hampshire (UNH) in both sides of the Atlantic (East and West). Different tagging technologies were combined, with the aim of gaining further insight on juvenile migration patterns, habitat use and feeding behaviors. In the Bay of Biscay, the following tagging objectives were established within the “Hegalabur 2009” survey:

− 78 internal Lotek archival tags (31 LAT and 47 LTD) in 1 and 2 year old individuals.

− 7 Microwave telemetry X-tags on > 2 year old individuals

− 1000 conventional tags in 1 year old individuals

In the western Atlantic, 54 Xtags (Galuardi et al. SCRS/2009/151) and 132 archival tags have been deployed on 2-4 year old and 3-6 year old individuals respectively between 2005 and 2008. 4. Progress and partial results In this section, some indications about survey performance and partial results are shown, referred to the period between June 26th and September 2nd, in which 10 fishing trips were completed. 4.1 Acoustic observation During the first ten fishing trips, 201 echosounder detections and 585 sonar detections were recorded. During the period with the echosounder (between 26th of June and the 22nd of July), a similar amount of detections were recorded with scientific echosounders and the long range sonar (201 and 233 respectively). Moreover, the number of daily detections with both acoustic technologies showed a linear relationship (Figure 3).

759

In spite of the relatively high number of tuna detections, tuna catches were scarce. During the first 10 fishing trips (69 days), 96 fishing operations were conducted. However, only 29 days with positive catch were recorded (15 days for bluefin tuna and 18 for albacore tuna). During several days of the survey, visual or acoustic observations (either by sonar or echosounder) of tuna were recorded whereas no fishing occurred, specially for BFT, as they did not react to the live bait (Figures 4 and 5). Consequently, BFT catches do not show a clear correlation with sonar observations (Figure 6), neither in terms of events nor quantitatively (number of individuals caught vs estimated local biomass), and neither at a daily nor a weekly timescale. On the contrary, in the case of albacore (ALB, Thunnus alalunga), clearer correlations were observed between catches and sonar observations (Figure 7), specially on a weekly scale. During this initial part of the survey, bluefin tuna were concentrated mainly at the southeastern corner of the Bay of Biscay (east of 4ºW, Figure 8). This preliminary analysis, and in particular the observation of BFTs not reactive to live bait, lets us suppose an important influence of tuna feeding behaviour on their catchability by baited gears (Stoner, 2004). Acoustic observation of tunas appears therefore an interesting complementary tool for a non-biased estimation of their abundance. After the bluefin quota for the baitboat fishery was over, acoustic observation continued until the end of the fishing season (with scientific echosounders and long range sonar in the FV Berriz Gure Naia and with long range sonar in two other baitboats). 4.2 Biological sampling Between July 6th and August 25th, 265 juvenile and adult bluefin were sampled (Table 1). Otoliths and samples for genetic studies (muscle, gill, heart and liver tissue) as well as stomachs were collected from most individuals. Samples were quite evenly distributed between commercial categories and time strata, with the exception of lack of samples from individuals between 25 and 40 kilo (this category was very badly represented in the overall baitboat catch). Additionally, 10 age-1 individuals were sampled on board the FV Berriz Gure Naia, in order to complete the sampling performed on commercial fish. 44 yearlings have also been sampled in the western Mediterranean in early October, and their otoliths and biopsies will be used as reference of the Mediterranean nursery ground. 4.3 Tagging Releases in the Hegalabur survey to date include 391 conventional tags 60-80 cm Fork Length (FL), 44 archival tags 60-84 cm FL and 4 X-tags 100-110 cm FL. In the western Atlantic, 3 X-tags were implanted to date on adult individuals, and 4 X-tags on juveniles. So far, three recoveries from previous internal archival release programmes have been obtained (Table 2). One recovery with 9 months at liberty was obtained from 14 releases performed by AZTI Tecnalia in 2005-2006. The other two recoveries occurred during the 2009 fishing season. One of them, with 2 years at liberty, belongs to the 144 releases in the joint AZTI-IEO program in 2007. The other one, with one year at liberty, was implanted in a joint AZTI-UNH action, in cooperation the sport-fishermen federation FASNAPER. Preliminary geolocations so far suggest that most of the juveniles spent the winter season between Azores and Portugal. 5. Perspectives Pending funding, it is expected that the survey, as well as analyses of the data and samples obtained this year, will continue in 2010 and following years. 5.1 Acoustics Continuous records of scientific echosounders will be analyzed and echointegrated with Movies software, in order to get biomass quantification. Sonar screenshots will be examined by image analysis. Catch and echosounder information, together with skippers’ expert knowledge will be used to try to develop an algorithm

760

capable of interpreting the signals and getting bluefin tuna abundance trends from sonar recordings. This software will allow interpreting the long range sonar signals recorded in a large number of collaborative baitboats. These studies might lead to the development of alternative abundance indices of bluefin tuna in the Bay of Biscay, and the methods might be applicable in other regions. Our results (and other authors) suggest that baitboat CPUE might not reflect bluefin abundance at different time scales, due to the fact that the probability of bluefin tuna being hooked when they are present is very variable. Given that, an abundance index based on sonar information could be advantageous in the sense that it would be independent of the bluefin tuna feeding behaviour, although it would still be based on the fishery (the fishery would operate normally and their sonar signals would be standardized instead of CPUEs). In the current situation, with increasing fishing limitations to the fishery in the recent years, and the fleet adapting their behaviour to the new situation, including self-imposed weekly quota systems, it might be even more advantageous to have a fishery independent abundance index. There are not many acoustic abundance indices in tunas (e.g. Hobday et al. 2009), probably because their ability to migrate over large distances well before an acoustic boat could cover the survey area. In an area such as the Bay of Biscay, where the bluefin tuna fishing ground is relatively limited (most catches occur in a 2ºx2º box), the scientific acoustic survey might be a good alternative. Several boats in paralell could be used in order to take “snapshots” of bluefin abundance along the fishing season. 5.2 Biological sampling We expect that contacts with scientists, fishermen and manufacturers will allow sampling fish from other areas, including the Gulf of Mexico nursery ground. Otolith microchemistry, genetic analyses, stable isotope analyses and ovary histology are planned to be performed in 2010. Through otolith microchemistry we plan to identify the origin and respective proportions of individuals born in the Mediterranean Sea and in the Gulf of Mexico among the BFT present in the Bay of Biscay. We also aim to determine the possible variability of this proportion over the fishing season or between age-groups. This analysis will be supported by genetic population structure analyses. This analysis will be complemented by genetic assignment of origin and genetic admixture analyses through DNA markers. Regarding genetic analyses, as a preliminary approach, microsatellites described in Takagi et al. (1999), McDowell et al. (2002) and Clark et al. (2004) will be used. However, SNP (Single Nucleotide Polymorphism) genotyping seems to be the alternative to microsatellites in a near future. They represent the most abundant class of polymorphisms in any organism, are adaptable to the automation, and reveal polymorphisms not detected by another type of markers and technologies. Moreover, the mutation rate of the SNPs is significantly minor to that of the microsatellites (Landegren et al. 1998, Nielsen 2000). On the other hand, and considering the biallelic nature of SNPs, the information provided by each SNP is minor to that of microsatellite loci, but the informative content can increase by means of the inclusion of a major number of SNPs (Glaubitz et al., 2003). SNPs are rapidly emerging as the preferred genetic markers for molecular genetic analysis (Rynnänen et al.2007), but there is a general lack of information about SNPs in the Thunnus genome. The University of the Basque Country, in collaboration with AZTI Tecnalia, has already discovered more than 50 SNPs. The intention is to continue this work and generate a pannel of 200-300 neutral and independent SNPs in Thunnus, to replace the microsatellite markers by SNPs for genetic studies. Stomach content and stable isotope analyses will complete, in terms of interannual variability, previous knowledge on the feeding ecology of BFT in the Bay of Biscay. Moreover, histological analyses on mature ovaries will allow identifying maturity stages, including eventual post-spawning evidences, of female BFT present in the Bay of Biscay. Together with otolith microchemistry and genetic analyses, these results will allow identifying eventual post-spawning migrations between spawning areas and the Bay of Biscay. 5.3 Tagging Tagging activities are also expected to continue in 2010. Further recaptures of bluefin tagged in the past with internal archival tags, as well as information provided by pop-up satellite archival tags, are expected in the

761

following months/years. This information will give a deeper insight on the movement patterns, mixing and habitat preferences of Atlantic juvenile bluefin tuna. Aknowledgements Special thanks to Jose Maria Salvador, Kati Lekuona and other staff from Bacaladera, for their willingness to collaborate in this research project. Luis Naval for his involvement in biological sampling, and Emilio Salaberria and Xebero Alkain, skippers of the FV Berriz Gure Naia, for their energy and experience dealing with both tuna and scientists. The Basque Government promoted and financed (together with the EU) this project. The Federación de Cofradías de Bizkaia and Federación de Cofradías de Gipuzkoa, as well as the sport fishing association FASNAPER have supported and contributed to the project in the Bay of Biscay. The recreational fishing association of Catalunya has collaborated in the obtention of samples from the Mediterranean. Richard Brill, Greg Skomal, Jessie Knapp, and Francois Royer also helped with the project in the western Atlantic. This part was funded by NOAA with Grant NA04NMF4550391 to M. Lutcavage. References Block, B.A., Teo, S.L.H., Walli, A., Boustany, A., Stokesbury, M.J.W., Farwell, C.J., Weng, K.C., Dewar, H.

and Williams, T.D. 2005, Electronic tagging and population structure of Atlantic bluefin tuna. Nature 434: 1121-1127.

Carlsson, J., McDowell, J.R., Carlsson, J.E.L., Olafsdottir, D. and Graves, J.E. 2006, Genetic heterogeneity of Atlantic bluefin tuna caught in the eastern North Atlantic Ocean south of Iceland. ICES Journal of Marine Science 63: 1111-1117.

Cort, J.L., de la Serna, J.M. 1994, Revision of tag/recapture of bluefin tuna (Thunnus thynnus, L.) in the East Atlantic and the Mediterranean. Collect. Vol. Sci. Pap. ICCAT, 42(1): 255-259.

de la Serna, J.M., Ortiz de Zárate, V., Gómez, M.J. 2001, Actualización de los datos de marcado - recaptura de atún rojo (Thunnus thynnus L.) en el Atlántico Este y Mediterráneo. Collect. Vol. Sci. Pap. ICCAT, 52(2): 784-792.

Fromentin, J.M. 2009, Lessons from the past: investigating historical data from bluefin tuna fisheries. Fish and Fisheries 10: 197-216.

Fromentin, J.M. and Powers, J.E. 2005, Atlantic bluefin tuna: population dynamics, ecology, fisheries and management. Fish and Fisheries: 281-306.

ICCAT 2004, Bluefin Tuna Research Program Planning Meeting (ICCAT Secretariat, 15-16 May 2003). Collect. Vol. Sci. Pap. ICCAT, 56(3): 987-1003.

ICCAT 2006, Report of the 2005 ICCAT Planning Meeting for Bluefin Tuna Research (Madrid, Spain, June 27 to 30, 2005). Collect. Vol. Sci. Pap. ICCAT, 59(3): 717-749.

ICCAT 2008, Report of the 2008 ICCAT Bluefin Tuna Stock Assessment Session (Madrid, June 23 to July 4, 2008). Collect. Vol. Sci. Pap. ICCAT, 64(1): 1-352.

Lutcavage, M.E., Brill, R.W., Skomal, G.B., Chase, B.C. and Howey, P.W. 1999, Results of pop-up satellite tagging of spawning size class fish in the Gulf of Maine: do north Atlantic bluefin tuna spawn in the mid-Atlantic? Can. J. Fish. Aquat. Sci. 56: 173-177.

Rodriguez-Marin, E., Arrizabalaga, H., Ortiz, M., Rodriguez-Cabello, C., Moreno, G. and Kell, L.T. 2003, Standardization of bluefin tuna, Thunnus thynnus, catch per unit effort in the baitboat fishery of the Bay of Biscay (Eastern Atlantic). ICES Journal of Marine Science 60: 1216-1231.

Rodríguez-Marín, E., Rodríguez-Cabello, C., de la Serna, J.M., Cort, J.L., Alot, E., Rey, J.C., Ortiz de Zárate, V., Gutierrez, J.L., Abad, E. 2005, A review of bluefin tuna juveniles tagging information and mortality estimation in waters around the Iberian Peninsula. Collect. Vol. Sci. Pap. ICCAT, 58(4): 1388-1402.

Rodriguez-Roda, J. 1969, Resultados de nuestras marcaciones de atunes en el Golfo de Cadiz en los años 1960 a 1967. Publ. Tec. Junt. Est. Pesca 8

Rooker, J.R., Bremer, J.R.A., Block, B.A., Dewar, H., Metrio, G.d., Corriero, A., Kraus, R.T., Prince, E.D., Rodríguez-Marín, E., Secor, D.H. 2007, Life history and stock structure of Atlantic Bluefin Tuna (Thunnus thynnus). Reviews in Fisheries Science 15, 265-310.

762

Ryynänen H.J., Tonteri A., Vasemägi A., and Primmer C.R. 2007, A comparison of biallelic markers and microsatellites for the estimation of population and conservation genetic parameters in Atlantic Salmon (Salmo salar). Journal of Heredity, 2007 doi:10.1093/jhered/esm093

Stoner, A.W. 2004, Effects of environmental variables on fish feeding ecology: implications for the performance of baited fishing gear and stock assessment. J. Fish Biol. 65

Table 1. number of sampled BFTs, by period and weight category, during the “Hegalabur 2009” project 8-15 kg individuals (mainly 2 year old)

otolith spine gill muscle liver heart stomach

July 1-15 4 - 3 4 4 4 4

July 16-31 37 12 27 36 34 17 29

August 1-15

16 - 16 16 16 16 16

August 16-31

21 - 20 21 21 14 21

Total 78 12 66 77 75 51 70

15-25 kg individuals (mainly 3 year old)

otolith spine gill muscle liver heart stomach gonad

July 1-15 31 25 4 32 32 27 30 17

July 16-31 23 - 23 23 17 6 24 -

August 1-15

23 - 25 25 25 14 25 -

August 16-31

16 - 16 16 15 6 17 -

Total 93 25 68 96 89 53 96 17

Individuals over 40 kg (adults)

otolith spine gill muscle liver heart stomach gonad

July 16-31 29 27 27 27 28 28 29 17

August 1-15

15 16 15 16 15 15 15 7

August 16-31

27 29 30 28 31 41 22 11

Total 71 72 72 71 74 84 66 35

Overall otolith spine gill muscle liver heart stomach gonad

Total 242 109 206 244 238 188 232 52

763

Table 2. Release and recovery dates, fork-lengths at release and recovery, periods of presence in the Bay of Biscay, maximum longitude and depth for three bluefin tagged with archival tags. Tag ID Time at liberty Length

Cm Age fish out of Bay of

Biscay, Dates. Max long

Max Depth

Days Start Finish St. Fin. St. Fin. St. Fin. WC390579 285 9/1/05 6/13/06 67 95 1 2 12/7/05 5/7/06 27º

W 760m

LTD1443 339 8/28/08 8/10/09 89 103 2 3 12/25/08 5/23/09 23º W

1050m

WC 390540

715 8/18/07 64 1 2 12/27/07 5/31/08 34º W

890m

8/2/09 102 2 3 11/10/08 6/16/09 53º W

970m

Figure 1. Example of a long range sonar detection of a bluefin school.

764

Figure 2. Echosounder screenshot showing a school of BFT between 10 and 20 m depth (38 and 120 kHz frequencies), and between 20 to 50 m aside the boat (200 kHz frequency)

Figure 3. Relationship between number of detections with scientific echosounders and long range sonar between 26th of June and 22nd of July.

R2 = 0.5976

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Nº sonar detections per day

Nº

eco

sou

nd

er d

etec

tio

ns

per

day

765

Figure 4. Daily fishing events and echosounder detections of BFT from the FV Berriz Gure Naia. Green dots indicate that the boat was not at sea.

766

Figure 5. Daily catches and sonar detections of BFTs from the FV Berriz Gure Naia: Upper pannel indicates the number of fishing events and the number of sonar detections. The lower pannel indicates the catch in number of fish and the quantity of fish detected by the sonar (as estimated by the skipper empirically). Green dots indicate that the boat was not at sea.

767

Figure 6. BFT catches plotted versus sonar detections, in terms of events (left panels) and quantitatively (right panels); daily (upper panels) and weekly (lower panels).

768

Figure 7. ALB catches plotted versus sonar detections, in terms of events (left panels) and quantitatively (right panels); daily (upper panels) and weekly (lower panels).

769

Figure 8. Spatial distribution of BFT (red circles) and ALB (green circles) sonar detections, between 26th June and 22nd July. The size of the points is proportional to an empirical abundance estimate from the skipper.