On-Going Albacore Research in the Bay of Biscay (Northeast Atlantic): the “Hegaluze 2010” Project

SCRS/2010/156 Collect. Vol. Sci. Pap. ICCAT, 66(5): 1956-1965 (2011)

ON-GOING ALBACORE RESEARCH IN THE BAY OF BISCAY (NORTHEAST ATLANTIC): THE “HEGALUZE 2010” PROJECT

Nicolas Goñi1, Igaratza Fraile1, Igor Arregui1, Josu Santiago2, Urtzi Laconcha1,3, Andone Estonba3, Haritz Arrizabalaga1

SUMMARY

In spite of an old exploitation, numerous uncertainties remain regarding the North Atlantic albacore (Thunnus alalunga) population. The actual geographic and vertical extension of their habitat in the North Atlantic, their migration patterns, and their possible genetic heterogeneity are still poorly known. Moreover, albacore catches may not correctly reflect their local abundance, due to a variable catchability. In this context, the main objective of the ongoing "Hegaluze 2010" project is to understand albacore stock structure, distribution and migrations in the North Atlantic through the application of individual markers (electronic tags, genetic markers, microchemistry). The project also aims to assess the possibility of using acoustic technologies (sonar) to get abundance indices of albacore in the Bay of Biscay and surrounding waters, and to analyze the influences of hydroclimatic parameters on albacore catchability, local abundance and recruitment. Electronic tagging, biological sampling, microchemistry and genetic analysis are ongoing. Partial results for tagging are presented and some possibilities for developing acoustic indices of abundance are discussed, as well as the perspectives for different analyses (tagging, otolith microchemistry, genetics, muscle and liver stable isotopes, and time-series analyses).

RESUME

Malgré une exploitation ancienne, de nombreuses incertitudes persistent quant à la population de germon (Thunnus alalunga) de l'Atlantique Nord. L'extension réelle de leur habitat géographique et vertical dans l'Atlantique Nord, leurs schémas migratoires et leur possible hétérogénéité génétique sont encore mal connus. En outre, les captures de germon pourraient ne pas correctement refléter leur abondance locale, du fait d'une capturabilité variable. Dans ce contexte, l'objectif principal du projet « Hegaluze 2010 » en cours est de mieux comprendre la structure, la distribution et les migrations de la population de germon dans l'Atlantique Nord, par l'usage de marqueurs individuels (marques électroniques, marqueurs génétiques, microchimie). Le projet a également pour objectif de tester la possibilité d'utiliser des technologies acoustiques (sonar) visant à obtenir des indices d'abondance de germon dans le golfe de Gascogne et les zones adjacentes, et d'analyser les influences de paramètres hydroclimatiques sur la capturabilité, l'abondance locale et le recrutement des germons. Le marquage électronique, l'échantillonnage biologique et les analyses microchimiques et génétiques sont en cours. Les résultats partiels pour le marquage sont présentés et les possibilités de développer des indices acoustiques d'abondance sont discutées, ainsi que les perspectives pour les différentes analyses (marquage, microchimie d'otolithes, génétique, isotopes stables du muscle et du foie et analyses de séries temporelles).

RESUMEN

Si bien la población de atún blanco (Thunnus alalunga) del Atlántico Norte se ha explotado ancestralmente, persisten muchas incertidumbres al respecto. Poco se conoce todavía sobre la extensión real de su hábitat geográfico y vertical, sus esquemas migratorios, y su posible heterogeneidad genética. Además, las capturas de atún blanco podrían no reflejar correctamente su abundancia local, debido a una capturabilidad variable. En ese contexto, el objetivo principal del proyecto "Hegaluze 2010" en curso es entender mejor la estructura, la distribución y las migraciones de la población de atún blanco en el Atlántico Norte, mediante el uso de marcadores individuales (marcas electrónicas, marcadores genéticos, microquímica). El

1 AZTI Tecnalia. Herrera Kaia Portualdea z/g. 20110 Pasaia, Gipuzkoa, Spain. Corresponding author: [email protected] 2 AZTI Tecnalia. Txatxarramendi Ugartea z/g. 48395 Sukarrieta, Bizkaia, Spain. 3 Genetika, Antropologia Fisikoa eta Animalien Fisiologia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU), PO Box 48080, Bilbao, Spain. 1956 proyecto también tiene como objetivo probar la posibilidad de usar tecnologías acústicas (sonar) para obtener índices de abundancia de atún blanco en el Golfo de Vizcaya y aguas adyacentes, y analizar las influencias de parámetros hidroclimáticos sobre la capturabilidad, la abundancia local y el reclutamiento de los atunes blancos. El marcado electrónico, el muestreo biológico y los análisis microquímicos y genéticos están en curso. Se presentan los resultados parciales para el marcado y se discuten las posibilidades de desarrollar índices acústicos de abundancia, así como perspectivas para los diferentes análisis (marcado, microquímica de otolitos, genética, isótopos estables de músculo e hígado y análisis de series temporales).

KEYWORDS

North Atlantic, albacore, Bay of Biscay, migration, tagging, genetics, microchemistry, acoustics

1. Introduction

Albacore is a highly migratory tuna species, found in the temperate and tropical waters of the Atlantic, Indian and Pacific Ocean, and in the Mediterranean Sea. The North Atlantic albacore stock has been exploited during several centuries in the Eastern North Atlantic, and in the whole North Atlantic Ocean during the 20th century mainly through the development of longline fisheries. This species is currently of high economic interest for West-European fishing fleets (Spanish and French fleet principally, and Irish and Portuguese fleet to a lesser extent).

North Atlantic albacore annual catches reached a maximum around 60 000 tons in the mid 1960’s, and followed a globally decreasing trend thereafter, this decreasing trend being partly due to a decrease of the global fishing effort (Santiago, 2004). In parallel to this decrease in fishing effort, the spatial distribution of this fishing effort was also reduced. Most of the catches are performed today in the Bay of Biscay and surrounding waters (ICCAT, 2010), and comprise 90% of immature individuals (up to age-4). Albacore caught in the rest of the North Atlantic are essentially longline bycatch.

In spite of this decreasing effort, the North Atlantic albacore stock assessment indicates a situation of over- exploitation (ibid.). This diagnostic may have several causes. On the one hand, this can be related to a loss of resilience of the population (Bard, 2003), essentially due to poor recruitments in a context of globally positive NAO winter values in the last decades (Borja and Santiago, 2002). On the other hand, the apparent situation of over-exploitation can be due to a biased perception of the actual resource. According to Fonteneau (2008), the current catches do not correctly reflect the evolution of the North Atlantic albacore population, which possibly comprises a “cryptic” biomass (Bard, 2001) whose geographical and vertical extension makes it unavailable to current surface fisheries operating in the Bay of Biscay and surrounding waters.

These uncertainties regarding the actual exploitation level of North Atlantic albacore, in spite of its long exploitation, result from important uncertainties on basic population parameters. Which is the actual geographical and vertical extension of albacore habitat in the North Atlantic? Are there different patterns of migration of immature individuals in summer months? Are there at least two sub-populations, as previously hypothesized by Aloncle and Delaporte (1974)? Which is the actual level of genetic heterogeneity among North Atlantic albacore? Do catches correctly reflect albacore local abundance?

In such a context, the interest of individual markers (Fromentin et al., 2009) such as electronic tags, genetic markers, and otolith microchemistry, is granted. Moreover, albacore catchability can be affected by several hydroclimatic parameters (Bard 2001, Goñi and Arrizabalaga 2005), which can be a source of bias for the stock assessment, as this assessment uses CPUE data as abundance indices. Direct estimations of local albacore biomass, through acoustic tools (Bertrand, 1999) would therefore be an interesting way to get alternative unbiased abundance indices. Finally, further analysis of historical catch and effort data can give a better insight on the long-term trends of albacore abundance and catchability in the Bay of Biscay.

1957 2. Objectives of the project

The project “Hegaluze 2010” aims to:

- understand albacore distribution and migrations in the North Atlantic, with a particular focus on the hydroclimatic conditions that characterize their habitat and migration paths. - identify a possible population heterogeneity among North Atlantic albacore, and potential variability in the geographical distribution of eventual subgroups. - assess the possibility of using acoustic technologies (sonar) to get abundance indices of albacore in the Bay of Biscay, and compare acoustic estimates with CPUE-based estimates. - analyze the influences of hydroclimatic parameters on catchability and/or recruitment.

3. Material and methods

The “Hegaluze 2010” project is being conducted during the whole albacore fishing season in the Bay of Biscay. The scientific work is divided into 3 tasks:

3.1 Tagging

Different tagging technologies were combined, with the aim of gaining further insight on juvenile migration patterns, habitat use and feeding behaviors.

The following tagging objectives were established within the “Hegaluze 2010” survey:

- 49 internal Lotek LAT2810 archival tags in 2 and 3 year old individuals. - 20 Microwave Telemetry X-tags on 4 year old individuals - 10 Wildlife Computers miniPAT tags on 5 year old individuals - Tagging activities were designed according to the tagging technologies used, and to the usual seasonal patterns of presence of albacore from different age-groups. Tagging operations for 2 and 3 year old individuals were conducted onboard a trolling boat (FV Almirante Berria) in June 2010. Tagging of 4 and 5 year old individuals is being performed onboard a baitboat (FV Tuku-Tuku), from August through October 2010.

In addition to these tags, the objective of 7 Microwave telemetry X-tags was set, in continuity of the Hegalabur 2009 project (see Goñi et al., 2010).

3.2 Biological sampling

Biological samples were taken from fish caught during the tagging surveys. Besides onboard sampling, fish manufacturers were contacted for access to fish being processed.

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 eventual different nursery grounds and migratory patterns, by mean of microchemical analyses. Otoliths will also be used together with dorsal fin spines to determine the age of the individuals. - Muscle biopsy to study population structure, using genetic analyses. - Muscle and liver for feeding ecology and migration studies using stable isotope analyses - Stomachs for feeding ecology studies through diet analyses

3.3 Acoustic observation

Baitboats use long range sonars as the main way to detect tuna schools. Sonar screenshots are recorded on 5 baitboats during the whole albacore fishing period. Image analysis of the screenshots is in progress with the intent of counting the number of albacore school detections and getting an abundance index.

1958 In parallel, tuna catches on all fishing operations during the 2nd part of the tagging survey are recorded to allow comparison between sonar detections and tuna catches. Empirical skipper estimates of the biomass detected by the sonar are also recorded in the FV Tuku-Tuku.

Besides this, albacore school detections performed in 2009 by sonar and echosounder during the Hegalabur 2009 survey (ibid.) are also being analyzed.

3.4 Time-series analyses

Albacore and bluefin historical daily landing data of the 20th century are being recovered from the Basque ports of Lekeitio, Ondarroa, Getaria and Hondarribia. As complementary information, historical monthly catches of the second half of 20th century are also being recovered from the port of Ziburu, where the baitboat fishery started in the late 1940s.

Once the recovery completed, the variability of these data will be analyzed at different time-scales in function of several hydroclimatic parameters, in order to look for environmental influences on tuna local abundance and catchability.

4. Progress and partial results

4.1 Tagging

Releases in the Hegaluze 2010 survey to date include 39 archival tags (fish size-range 60-90 cm FL) from June 7th to 15th, and 2 X-tags (fish sizes 84 and 96 cm FL) on August 23rd and September 20th respectively. The survey also allowed tagging 7 bluefin tunas (86 to 97 cm FL) with X-tags, in continuity of the Hegalabur 2009 project (ibid.).

So far, 1 recovery from previous pop-up tag release programs has been obtained. Preliminary geolocations of the tagged individual (Lam et al. 2008) showed that it left the Bay of Biscay on October 30th, then migrated southwards (Figure 1). Its depth distribution appeared relatively shallow (Figure 2), being more than 95% of the time within the upper 50 m in the Bay of Biscay, and within the upper 100 m off Portugal, after October 30th. One of the 39 archival tags deployed was recovered on August 8th.

4.2 Biological sampling

Between June 6th and September 13th 2010, 569 juvenile albacore caught by trolling line (n=180), baitboat (n=277) and pelagic trawling (n=112) were sampled (Table 1), during the survey, on port and in fish manufactures. Muscle or pectoral fin samples for genetic studies were taken from all of them. Otoliths, stomachs as well as muscle and liver samples for stable isotope measurements were collected from 431 of them, sampled in manufactures. Samples are quite evenly distributed between commercial categories and time strata (Table 1), with the exception of individuals under 4 kg and over 14.5 kg (these categories were very poorly represented in the overall catch, either in the trolling, baitboat of trawling fleet). The sampling is currently going on and will continue until the end of the albacore fishing season.

In addition to the individuals sampled in 2010, samples from 223 albacore caught in 2009 were also collected (Table 2), both in 2009 and in 2010 (frozen fish in manufactures).

4.3 Acoustic observation

During the fishing trips performed in 2009, 36 echosounder detections and 196 sonar detections (Figure 3) of albacore were recorded onboard the FV Berriz Gure Naia. During the periods with the echosounder (June 26th to July 22nd, and October 6th to 11th of 2009), 36 albacore detections were recorded with scientific echosounders and 59 with the long range sonar.

In spite of the relatively high number of tuna detections, tuna catches were scarce. During the 12 fishing trips (85 days), only 23 days with positive albacore catches were recorded, corresponding to 65 fishing operations. Correlations were observed between catches and sonar observations (Figure 4), especially on a weekly scale. On a smaller time-scale (day), these correlations are not so clear.

1959 During the fishing trips performed in 2010 since August 23rd, 47 sonar detections have been recorded. The data will start to be analyzed at the end of the tagging survey.

4.4 Time-series analyses

To date, daily albacore and bluefin tuna landings per vessel have been gathered from the ports of Lekeitio, Ondarroa and Hondarribia. Data from 10 years-ports are still being recovered (details in Table 3), and most of the available data are fully recovered to date. For the port of Hondarribia, the number of records recovered represents 45258 trips conducted by 373 vessels during 29 years. In Ondarroa 48511 records have been recovered to date, and over 50000 in the case of Lekeitio.

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 2011 and following years.

5.1 Tagging

Tagging activities are expected to continue in 2011. Further recaptures of albacore tagged with internal archival tags, as well as information provided by pop-up satellite archival tags, are expected in the following months/years. This information will give a deeper insight on the migration paths, movement patterns, and habitat preferences of North Atlantic albacore.

5.2 Biological sampling

We expect that contacts with scientists, fishermen and manufacturers will allow further sampling of North Atlantic albacore in the following years, as well as albacore from other areas, including the South Atlantic and the Eastern Mediterranean Sea. Otolith microchemistry, genetic analyses, and stable isotope analyses are planned to be performed in 2011.

Further microchemistry analyses on the sampled otoliths, and multivariate analysis of the data can allow us to identify possible different nursery grounds and life-history migration patterns among North Atlantic albacore. We also aim to determine the possible variability – over the fishing season, geographically, or between age- groups – of the proportion of individuals from different nursery ground and with different life-history migration patterns. Microchemistry analysis will be complemented by genetic assignment of origin and genetic admixture analyses through DNA markers such as SNPs (Velado et al. 2010).

Stomach content and stable isotope analyses will complete, in terms of interannual variability, previous knowledge on the feeding ecology of albacore in the Bay of Biscay and surrounding waters. In particular, our sampling may allow us to give a deeper insight to the hypothesis by Das et al. (2000) on subgroups with different δ15N concentration among North Atlantic albacore.

Moreover, stable isotope analyses will allow estimating the period of arrival of albacore to the Bay of Biscay and surrounding waters. Together with otolith microchemistry and tagging data, these results will allow identifying an eventual variability in migration paths over the fishing season or between age-groups.

5.3 Acoustics

Sonar screenshots recorded in 2009 and 2010 will be examined by image analysis. Catch and echosounder information, together with skippers’ expert knowledge will be used to try to develop an algorithm capable of interpreting the signals and getting albacore 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 albacore in the Bay of Biscay, and the methods might be applicable in other regions. Given that, an abundance index based on sonar information could be advantageous in the sense that it would be independent from the albacore 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).

1960 5.4 Time-series analyses

Data recovery will be continued until the gaps are fulfilled and the complete 20th century is covered. Recovery from other Basque ports (Bermeo, Getaria) is also planned, in order to get a more complete insight on historical tuna catches by the Basque fleet.

Temporal variations of the landing data will be analyzed at different time-scales. Their relationships with broad- scale hydroclimatic variables (North Atlantic Oscillation, Eastern Atlantic Pattern) will indicate long-term trends of albacore recruitment and migration patterns to the Bay of Biscay. Their relationship with smaller-scale variables in the Bay of Biscay (SST, sea surface agitation, sunlight duration, wind speed and direction, rainfall, upwelling indices) will be indicative of hydroclimatic influences on their local abundance and catchability.

Acknowledgements

Special thanks to Jean-Hilaire de Bailliencourt and Johan Labadesse from SARL Batteleku, and to Maria-Jesus Sorazu and Sebastian Aranguren from Conservas Nardin S.L., for their interest and willingness to collaborate in this research project. To Luis Naval for his involvement in biological sampling, and to Telmo Martinez and Norberto Emazabel, respective skippers of the FVs Almirante Berria and Tuku-Tuku, for their energy and experience dealing with both tuna and scientists. To Molly Lutcavage and Ben Galuardi for their technical advice on pop-up tags. The Basque Government promoted and financed (together with the EU) this project. The GBYP of ICCAT has also contributed funding the recovery of historic data. 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.

References cited

Aloncle, H., Delaporte, F. 1974, Données nouvelles sur le germon Atlantique (Thunnus alalunga Bonnaterre 1788) dans le nord-est Atlantique. 2ème Partie. Rev. Trav. Inst. Pêches Marit. 38(1): 5-102. Bard, F.X. 2001, Extension of the geographical and vertical habitat of albacore (Thunnus alalunga) in the North Atlantic. Possible consequences on true rate of exploitation of this stock. Collect. Vol. Sci. Pap. ICCAT, 52(4): 1447-1456. Bard, F.X. 2003, North Atlantic albacore (Thunnus alalunga) past and present fisheries. Did the stock loose its resilience? Collect. Vol. Sci. Pap. ICCAT, 55(1): 251-271. Bertrand, A. 1999, Le système thon-environnement en Polynése Française : caractérisation de l’habitat pélagique, étude de la distribution et de la capturabilité des thons, par méthodes acoustiques et halieutiques. Thèse de l’Ecole Nationale Supérieure Agronomique de Rennes, 295 p. Borja, A., Santiago, J. 2002, Does the North Atlantic Oscillation control some processes influencing recruitment of temperate tunas? Collect. Vol. Sci. Pap. ICCAT, 54(4): 964-984. Clark, T.B., Ma. L., Saillant, E. and Gold, J.R. 2004, Microsatellites DNA markers for population-genetic studies of Atlantic bluefin tuna (Thunnus thynnus thynnus) and other species of genus Thunnus. Molecular Ecology Notes 4: 70-73. Das, K., Lepoint, G., Loizeau, V., Debacker, V., Dauby, P., Bouquegneau, J.M. 2000, Tuna and dolphin associations in the Northeast Atlantic: evidence of different ecological niches from stable isotope and heavy metal measurements. Marine Pollution Bulletin 40(2): 102-109. Fonteneau, A. 2008, Some comments on the 2007 North Atlantic albacore stock assessment. Collect. Vol. Sci. Pap. ICCAT, 62(3): 944-950. Fromentin, J.M., Ernande, B., Fablet, R., de Pontual, H. 2009, Importance and future of individual markers for the ecosystem approach to fisheries. Aquatic Living Resources 22(4): 395-408. Glaubitz, J.C., Rhodes, O.E. and Dewoody, J.A. 2003, Prospects for inferring pairwise relationships with single nucleotide polymorphisms. Molecular Ecology 12: 1039-1047. Goñi, N., Arrizabalaga, H. 2005, Analysis of juvenile North Atlantic albacore (Thunnus alalunga) catch per unit effort by surface gears in relation to environmental variables. ICES Journal of Marine Science 62(7): 1475–1482.

1961 Goñi, N., Fraile, I., Arregui, I., Santiago, J., Boyra, G., Irigoien, X., Lutcavage, M., Galuardi, B., Logan, J., Estonba, A., Zudaire, I., Grande, M., Murua, H., Arrizabalaga, H. 2010, Ongoing bluefin tuna research in the Bay of Biscay (Northeast Atlantic): the “Hegalabur 2009” project. Collect. Vol. Sci. Pap. ICCAT, 65(3): 755-769. Hobday, A., Kawabe, R., Takao, Y., Miyashita, K., Itoh, T. 2009, Correction factors derived from acoustic tag data for a juvenile southern bluefin tuna abundance index in southern western Australia. In: Nielsen, J.L., Arrizabalaga, H., Fragoso, N., Hobday, A., Lutcavage, M., Sibert, J., editors. Reviews: Methods and Technology in Fish Biology and Fisheries: Tagging and Tracking of Marine Animals with Electronic Device. London: Springer. pp 405-422. ICCAT, 2010, Report of the 2009 ICCAT Albacore Stock Assessment Session (Madrid, Spain, July 13 to 18, 2009). Collect. Vol. Sci. Pap. ICCAT, 65(4): 1113-1253. Lam, C.H., Nielsen, A., Sibert, J.R. 2008, Improving light and temperature based geolocation by unscented Kalman filtering. Fisheries Research 91: 15-25. Landegren, U., Nilsson, M. and Kwo,k P.Y. 1998, Reading bits of genetic information: methods for single- nucleotide polymorphism analysis. Genome Research 8: 769-776. McDowell, J., Diaz-Jaimes, P. and Graves, J.E. 2002, Isolation and characterization of seven tetranucleotide microsatellite loci form Atlantic northern bluefin tuna Thunnus thynnus thynnus. Molecular Ecology Notes 2: 214-216. Nielsen, R. 2000, Estimation of population parameters and recombination rates using single nucleotide polymorphisms. Genetics 154: 931-942. Ryynänen, H.J., Tonteri, A., Vasemägi, A., 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). The Journal of Heredity, 98: 692-704 Santiago, J., 2004, Dinámica de la población de atún blanco (Thunnus alalunga Bonnaterre 1788) del Atlántico Norte. PhD Thesis, Euskal Herriko Unibertsitatea, Bilbao, 320 pp. Takagi, M., Okamura, T., Chow, S. and Taniguchi, N. 1999, PCR primers for microsatellite loci in tuna species of the genus Thunnus and its application for population genetic study. Fisheries Science 65, 571-576. Velado, I., Laconcha, U., Zarraonaindia, I., Iriondo, M., Manzano, C., Arrizabalaga, H., Pardo, M.A., Goñi, N., Heinisch, G., Lutcavage, M., Estonba, A. 2010, SNP discovery in Thunnus alalunga and T. thynnus for genetic diversity and population structure analyses. SCRS/2010/118.

1962 Table 1. Distribution, by landing period and weight category, of the albacore sampled during the Hegaluze 2010 project between June 6* and October 25. Total sampled number, and – in parenthesis – number of individuals sampled for genetics only.

Weight category / < 4 kg 4-7 kg 7-11 kg 11-14.5 kg > 14.5 kg Landing period 16-30th June - 80 (62) 38 (28) 5 (3) - 1-15th July - 95 31 2 - 16-31st July - 73 71 4 1 1-15th August 4 (4) 11 (11) 10 (6) 15 (7) 2 (2) 16-31st August - 20 42 24 - 1-15th September - 10 16 (6) 13 (13) 2 (2) 16th-30 September 47 5 5 20 5 1-15th October - - 1 21 58 16-30th October 1 - - 4 17 * Fish sampled during the first tagging survey were landed after June 16th

Table 2. Distribution, by weight category, of albacore caught in 2009 and sampled in 2010. Total sampled number, and – in parenthesis – number of individuals sampled for genetics only. Weight category < 4 kg 4-7 kg 7-11 kg 11-14.5 kg > 14.5 kg Number 60 21 32 116 (96) 1

Table 3. Recovery of historical daily landing data from the ports of Lekeitio, Ondarroa and Hondarribia, by year since 1930. Lekeitio Ondarroa Hondarribia Data recovered Data partially 1930s No data available

1940s

1950s

1960s

1970s

1980s

1963

Figure 1. Geographical displacement of a 91 cm long albacore tagged on October 8, 2008 in the Bay of Biscay. Pop-off on December 11, 2008 off Portugal. Latitude and longitude data corrected through unscented Kalman filtering.

Figure 2. Depth (green dots and curve, left axis) and ambient temperature (orange dots and curve, right axis) of a 91 cm long albacore tagged on October 8, 2008 in the Bay of Biscay. Pop-off on December 11, 2008 off Portugal.

1964

Figure 3. Example of a long range sonar detection of an albacore school

Figure 4. Albacore catches plotted versus sonar detections in 2009, in number of events (left panels) and quantitatively (right panels); daily (upper panels) and weekly (lower panels).

1965