BACK ESTIMATE OF WEIGHT AT CATCH OF ATLANTIC BLUEFIN TUNA FISHED AND FARMED IN THE MEDITERRANEAN IN 2008 BASED ON DATA FROM THE JAPANESE FRESH MARKET

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1 SCRS/2010/068 Collect. Vol. Sci. Pap. ICCAT, 66(3): (2011) BACK ESTIMATE OF WEIGHT AT CATCH OF ATLANTIC BLUEFIN TUNA FISHED AND FARMED IN THE MEDITERRANEAN IN 2008 BASED ON DATA FROM THE JAPANESE FRESH MARKET ATRT 1, Greenpeace 2, MarViva 3, WWF 4 SUMMARY Fish weight at catch was back-calculated individually for a total of 8,020 Atlantic bluefin tuna specimens fished and farmed in the Mediterranean Sea in 2008 and auctioned fresh in Japan, using the latest data endorsed by SCRS on weight gain rates in farms. The results obtained showed that overall 56 % of the tunas caught and caged in Mediterranean Sea farms and auctioned fresh in the Japanese market would have been below the 30-kg legal minimum catch size at the start of farming. Undersized, illegally caught fish would amount to 70 % of the total sample in the case of Spain. The authors warn these results might point to the unreliability of the new weight gain rates adopted last year. RÉSUMÉ Le poids du poisson à la capture a été rétro-calculé individuellement pour un total de spécimens de thon rouge de l Atlantique pêchés et engraissés en Méditerranée en 2008 et vendus à la criée à l état vivant au Japon, en utilisant les toutes dernières données entérinées par le SCRS sur les taux de gain pondéral dans les fermes. Les résultats obtenus ont montré que globalement 56% des thons capturés et mis en cages dans des fermes méditerranéennes et vendus à la criée à l état frais sur le marché japonais auraient été en-deçà de 30 kg, qui est la taille de capture minimum légale au début de l engraissement. Dans le cas de l Espagne, des poissons sous-taille et capturés illégalement représentaient 70% de l échantillon total. Les auteurs ont averti que ces résultats pourraient signaler le manque de fiabilité des nouveaux taux de gain pondéral adoptés l an dernier. RESUMEN Se ha calculado retrospectivamente el peso de los peces en el momento de la captura, de forma individual, para un total de ejemplares de atún rojo del Atlántico pescados e introducidos en instalaciones de engorde en el Mediterráneo en 2008 y subastados en fresco en Japón, utilizando los últimos datos respaldados por el SCRS sobre las tasas de ganancia de peso en las instalaciones de engorde. Los resultados obtenidos mostraban que, en conjunto, el 56% de los atunes capturados e introducidos en jaulas en las instalaciones de engorde del Mediterráneo y subastados frescos en el mercado japonés, se encontrarían por debajo de la talla de captura mínima legal de 30 kg en el inicio de su engorde. Los peces de talla inferior a la regulada capturados ilegalmente ascenderían al 70% de la muestra total en el caso de España. Los autores advierten de que estos resultados podrían indicar la poca fiabilidad de las nuevas tasas de ganancia de peso adoptadas el año pasado. KEYWORDS Thynnus thynnus, farming, weight gain rates, size at catch 1 Advanced Tuna Ranching Technologies, S.L. 2 Greenpeace Internacional. San Bernardo, 107, Madrid, Spain 3 MarViva. P.O. Box 99, Andratx, Mallorca, Spain 4 WWF, Mediterranean Programme Office. Canuda, 37, Barcelona, Spain. Corresponding author: studela@atw-wwf.org 1152

2 1. Introduction Studies carried out in Croatia, Greece, Malta and Spain of weight gain rates of Atlantic bluefin tuna in Mediterranean farms were reviewed by the SCRS in The studies revealed that growth of bluefin tuna in farms could be significantly higher than formerly believed. From this discussion a new table was created which showed weight gain rates based on information presented to the Committee at that time. The aim of the present paper is to use the new rates endorsed by SCRS to back estimate weight at catch of farmed Mediterranean bluefin tuna sold fresh in Japanese markets in We chose 2008 as this is the most recent and complete series of data from the Japanese market available to date. 2. Materials and Methods Information on 8,020 Atlantic bluefin tuna specimens was obtained by ATRT from 50 Japanese fish auction markets situated in 19 different locations (Table 1). The locations included: Chiba, Fukuoka, Funabashi, Ishikawa, Kanazawa, Kawasaki, Koriyama, Kyoto, Nagoya, Oota, Osaka, Saitama, Sapporo, Sendai, Senju, Shiogama, Tokyo, Yamagata and Yokohama. All the data originated from daily auction records of bluefin tunas imported fresh from Mediterranean farms to Japan and auctioned in the aforementioned Japanese markets from 1 st July th June 2009 (attributed to the 2008 fishing season). The information gathered included all the tunas from Mediterranean farms imported fresh to Japan for which information on weight was available (=individually disclosed in the market reports). Only whole fish (dressed or gilled and gutted) were considered for this study. Tunas over 60 kg and auctioned fresh are typically dressed, whereas those below 60 kg are usually auctioned gilled and gutted, hence ICCAT's accepted conversion factors to round weight of 1.25 and 1.16, respectively, were applied. A second conversion rate is, therefore, needed to back-estimate the original weight-at-catch and to account for the increase in weight during the farming period. The table created after the SCRS discussion on fattening of Atlantic bluefin tuna (Table 16.6 of the 2009 SCRS Report; ICCAT, 2010) provides gain estimates (as percentages). Based on this table, we applied reverse fattening conversion factors to obtain the estimated weight-at-catch or wild round weight (RWT) prior to caging. In order to back-calculate the initial weight, when ex-cage weight didn t match any of the entries from Table 16.6 (i.e. when the value fell between two weights), we always used the smallest % weight gain factor, thus obtaining the highest wild RWT value and keeping a conservative approach at all times. Farming time was assessed individually assuming caging in June. All tuna individuals were sorted by auction date and market, country of origin and weight; and were grouped into 30-kg size classes based on the final estimates of weight at catch. 3. Results The estimated weight at catch of the Atlantic bluefin tunas auctioned fresh in Japanese markets in 2008 for which individual information was available showed that most of the individuals were less than 60 kg in weight (Figure 1a) prior their entrance into the cages. Out of a total of 8,020 auctioned tunas, 6,320 were less than 60 kg, from which 4,459 were less than 30 kg, which means that almost 56 % of all the tunas were less than 30 kg (Figure 1b). Regarding the tunas originating from Spain, from a total of 3,545 individuals, almost 2,500 were less than 30 kg, i.e. almost 70 % of the total (Figures 2a and 2b). 4. Discussion The issue on the growth/weight gain rates of farmed Atlantic bluefin tunas in the Mediterranean Sea constitutes one of the main knowledge gaps with potentially far-reaching effects on the management of the species. Indeed, selecting the right growth rate is essential to achieve an accurate back-estimate of farmed produced catches. For the past years, and based on some scattered available information, ICCAT has been using a conversion factor of 25% across-the-board. Last year, however, new information from industry-sponsored scientists was presented to the SCRS showing growth rates for Mediterranean farms much higher than those previously considered. Depending on size, they ranged between 39 and 180 % for a 6-month farming period, and from 41 to 256 % for a one year period (ICCAT, 2010). SCRS recommended the Contracting Parties to tentatively adopt growth factors consistent with the new data, which were integrated in tabular form into the official ICCAT report system (ICCAT, 2010). Here, for the first time, we individually applied the new rates to the complete set of specimens 1153

3 corresponding to a given fishing season (2008, in this case) which were auctioned fresh in the Japanese markets and for which information was individually disclosed in daily market reports. Unexpectedly, our results show that more than half of the fish (56%) were below the minimum legal catch size of 30 kg when they were fished and caged. An explanation based on the existing derogation for the Adriatic fishery can be ruled out because 1) only 89 fish (1.1% of the total sample size) came from Croatian farms and 2) these few fish were mostly large individuals (Table 1). Furthermore, in the case of the Spanish farms illegal sized fish amount to an astounding 70 %. The results obtained here call for a careful analysis. One possible explanation would be that massive illegal catches of undersized fish were indeed conducted in Given the large sampling size, including most of the tuna auctioned fresh in the Japanese markets, the capture of undersized juveniles would have had to be massive and widespread. An alternative explanation would consist in challenging the validity of the new weight gain rates endorsed last year by the SCRS, which contrasted by near one order of magnitude with rates previously used. Notwithstanding the evidence on juvenile catches gathered by the authors for the 2008 fishing season, the magnitude of the figures back-estimated here makes us favor the second explanation, i.e. the unreliability of the % weight gain data from Table 16.6 of the 2009 SCRS Report (ICCAT, 2010). In the light of the above conclusions we believe a new and fully independent study on growth rates in farms should be conducted, designed and carried out within the framework of the ICCAT Atlantic Wide Research Programme for Bluefin Tuna. Until results of an independent study are available and endorsed by the SCRS, we believe much lower precautionary figures should be employed. References ICCAT 2010, Report for Biennial Period, Part II (2009) Vol. 2 SCRS. Table 1. Information on Atlantic bluefin tuna farmed in 2008 and auctioned fresh in Japan included in this study. Country refers to farming country Country Sum of Weight of Auctioned Average weight at Count (n) BFT (Kg) auction Max Min Croatia 10, Greece 4, Italy 52, Malta 45, Spain 255,815 3, Tunisia 35, Turkey 205, , Grand Total 608,813 8,

4 (a) (b) Figure 1. Size frequencies of estimated wild round weight of Atlantic bluefin tuna farmed in the Mediterranean in 2008 and auctioned fresh in Japanese markets, showed as (a) total individuals and (b) in percentage. 1155

5 (a) (b) Figure 2. Size frequencies of estimated wild round weight of Atlantic bluefin tuna farmed in Spain in 2008 and auctioned fresh in Japanese markets, showed as (a) total individuals and (b) in percentage. 1156