SCRS/2009/128 Collect. Vol. Sci. Pap. ICCAT, 65(3): 755-769 (2010) 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: [email protected] 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. 755 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). 756 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.