PRELIMINARY RESULT OF POP-UP ARCHIVAL TAGGING FOR ATLANTIC BLUEFIN TUNA (THUNNUS THYNNUS) RELEASED IN THE NORTHEASTERN ATLANTIC OCEAN

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1 SCRS/28/179 Collect. Vol. Sci. Pap. ICCAT, 64(2): (29) PRELIMINARY RESULT OF POP-UP ARCHIVAL TAGGING FOR ATLANTIC BLUEFIN TUNA (THUNNUS THYNNUS) RELEASED IN THE NORTHEASTERN ATLANTIC OCEAN Yasuko Semba 1, Yukio Takeuchi 1 SUMMARY We report the preliminary analysis of migration of an Atlantic bluefin tuna which was tagged and released from the area off Ireland. This individual was caught on 29 September 27 and released after the attachment of a pop-up archival tag (PAT) at the location (48º-16ºN, 11º-5ºW). The length estimated by eye was 16 cm (FL). On 29March 28, this tag was popped off six months after the release as programmed, and transmitted the data for the past six months. This individual conducted transatlantic movement from the eastern to the western North Atlantic. Based on the distinct temporal pattern of maximum diving depth and average temperature (both on a daily basis), we identified three phases in movement pattern as follows. In the first phase (9/29-1/26), this individual stayed in a relatively limited area with shallow vertical movement in the warm water, and embarked on a long- distance movement to the west with deep vertical movement in the cold water in the second phase (1/27-2/6), and it stopped the large movement and stayed in the terminal area with shallow vertical movement in the cold water in the third phase (2/7-3/29). The oceanographic feature may be associated with this change of behavior, which needs to be confirmed in the future. In this result, the link between the eastern foraging ground and the western breeding area was not confirmed but the intercommunication between east and west in the Atlantic was supported. RÉSUMÉ Le présent document fournit l analyse préliminaire de la migration du thon rouge de l Atlantique qui a été marqué et remis à l eau au large de l Irlande. Ce spécimen a été capturé le 29 septembre 27 et remis à l eau après qu on lui eut apposé une marque-archive «pop-up» à l emplacement (48º-16ºN, 11º-5ºW). La longueur estimée à l œil nu était de 16 cm (LF). Le 29 mars 28, cette marque est remontée à la surface six mois après son apposition, comme cela avait été programmé, et elle a transmis les données des six mois antérieurs. Ce spécimen a réalisé des déplacements transatlantiques de l Est à l Ouest de l Atlantique Nord. Sur la base du schéma temporel distinct de la profondeur de plongée maximale et de la température moyenne (les deux sur une base journalière), nous avons identifié trois phases dans le schéma de déplacement, comme suit. Dans la première phase (9/29-1/26), ce spécimen est demeuré dans une zone relativement limitée, effectuant un déplacement vertical en eaux peu profondes et tempérées, il a ensuite effectué un déplacement à longue distance vers l ouest avec un déplacement vertical profond en eau froide au cours de la deuxième phase (1/27-2/6). Il a ensuite mis fin au grand déplacement et est resté dans la zone terminale avec un déplacement vertical en eaux peu profondes et froides au cours de la troisième phase (2/7-3/29). La caractéristique océanographique pourrait être associée à ce changement de comportement, qui doit être confirmé à l avenir. Dans ce résultat, le lien entre la zone de recherche de nourriture à l est et la zone de reproduction à l ouest n a pas été confirmée, mais l intercommunication entre l est et l ouest dans l Atlantique a été soulignée. RESUMEN Este documento informa sobre el análisis preliminar de la migración de un atún rojo del Atlántico que fue marcado y liberado en aguas de Irlanda. Este ejemplar fue capturado el 29 de septiembre de 27 y liberado tras colocársele una marca archivo pop-up (PAT) en 48º-16ºN, 11º-5ºW. La talla estimada a la vista era de 16 cm (FL). El 29 de marzo de 28 esta marca emergió seis meses después de la liberación tal y como estaba programado y transmitió los datos de los seis meses anteriores. Este ejemplar realizó movimientos transatlánticos desde el Atlántico norte oriental hacia el occidental. Basándose en el patrón temporal separado de la profundidad máxima de inmersión y la temperatura media (ambas diarias), identificamos tres fases en el patrón de movimiento. En la primera fase 1 National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Orido, Shimizu-ku, Shizuoka City, Shizuoka Prefecture, Japan. 662

2 (9/29-1/26), este ejemplar permaneció en un área relativamente limitada con movimientos verticales superficiales en agua templada e inició un movimiento de larga distancia hacia el Oeste con movimientos verticales profundos en agua fría en la segunda fase (1/27-2/6), y en la tercera fase (2/7, 3/29) paró el movimiento de larga distancia y permaneció en la zona terminal con movimientos verticales superficiales. Las características oceanográficas pueden estar asociadas a este cambio de comportamiento, pero esto debe confirmarse en un futuro. En este resultado, el vínculo entre la zona de alimentación oriental y la zona de cría occidental no fue confirmado pero se respaldó la intercomunicación en el Atlántico entre el Este y el Oeste. KEYWORDS Bluefin tuna, electronic tags, migrations, fish behaviour 1. Introduction Many tagging research for Atlantic bluefin tuna (Thunnus thynnus) using popup archival tag (PAT) has been conducted in the northwestern Atlantic. The trans-atlantic movement from the west to the east area has been indicated by many studies (Lutcavage et al. 1999, Block et al. 21). However, the attempts that release the fish from the eastern area are relatively small. Recently, Stokesbury et al. (27) showed the trans- Atlantic movement from the east to west by tagging the fish from off the coast of Ireland. In this document, we introduce the additional information on the movement of this species released in the northeastern Atlantic. 2. Materials and methods On 29 th September 27, one pop-up archival tag (PAT: Microwave Telemetry Inc., PTT-1) was attached to a bluefin tuna (16cm FL: indicated as # thereafter) and released in the northeastern Atlantic (48-16N, 11-5W). At tagging, # was fixed with the head hoisted by the large gaff and the dart which was connected with PAT body via tether, was inserted into the dorsal muscle under the midpoint between the first and second dorsal fin from the side of vessel. This tag was set to pop off 6 months after the release and actually popped off on 29 th March 28 as programmed. Geo-location of the tag during days at liberty was initially provided from the manufacture (Microwave Telemetry Inc.). They were estimated from estimated time at sunrise and sunset. However as is usually happens, estimated positions (latitude, in particular) of tag were very erroneous. This is substantial around equinox. Therefore we used UKFSST; a R package to estimate geolocation through unscented Kalman filter (Lam et al. 28) to improve position estimates by including temperature information. Due to time constraint, for sea surface temperature we used daily average of temperature as a proxy of SST, while this would not be problem since in most of the case the individual stayed shallower water during the tag attached. Using the filtered data of position, we plotted the estimated point horizontally. In addition, we extracted the maximum diving depth for each day and calculated the daily average of temperature that this individual experienced. 3. Results and discussion The horizontal movement trajectory of # estimated from unscented Kalman filter was shown in Figure 1. Around equinox, large correction of position from light based position estimates in latitude was observed. At a large scale, # conducted trans-atlantic movement from autumn to spring with different pattern of movement. After released at in the area off Ireland (48-16N, 11-5W), it stayed about the area (4-5 N 1-2 W) during half of the days at liberty (9/29-1/6) and then began the travel to the west. In this movement, # moved directly to the west (1/7-2/12) and then changed the direction to the south (2/13-17). Reaching at the area (around 4 N, 38 W), it moved to the west again (2/18-2/23). After that, this individual stayed in relatively limited area (2/23-3/29). The change of temperature, with which this individual experienced, corresponded to this movement pattern to some extent. 663

3 Figure 2 shows the change of representative SST (smoothed by day) together with predicted one during the day at liberty. SST gradually dropped from18.8 to 15.5ºC (9/29-1/7) and then rapidly dropped to 12.6ºC and remained in the relatively stable range (1/8-2/12) and then rapidly increased to 17.4ºC (2/13-2/23) and then fluctuated largely (2/24-3/29). Based on the movement pattern, we tentatively divided the movement into 3 phases (1 st residence: 9/29-1/6, traveling period: 1/7-2/23, 2 nd residence: 2/24-3/29). Data on the daily maximum diving depth and daily average temperature was calculated using raw data and divided into each phase. Figure 3 shows the depth frequency in percentage by class for each phase. It suggests that diving depth in phase 1 tends to be shallower than 2m except one dive to 785m and most diving behavior was conducted within -1m. However, in phase 2, the maximum diving depth shifted to deeper (1-3m) and then the diving depth shifted to shallower depth again in phase 3. Figure 4 shows the temperature frequency in percentage by class for each phase. It suggests that #67681 experienced warmer temperature higher than 15 C in phase1 and then moved in the cooler water (mainly cooler than 15 C) in later phase. In phase3, the temperature that this individual experienced became cooler than that in phase2. As a result of comparing the depth distribution between night (18:-6:) and day (6:-18:) for each phase, temporal difference was observed (Figure 5). In phase 1, difference between night and day was small and depth distribution ranged mainly from to 1m. In phase 2, nocturnal depth distribution strongly biased to shallow water (<5m) while diurnal depth range shifted to deeper water than that in phase1. In phase 3, difference between night and day became small again except for the depth frequency from to 5m, in which range the frequency of diurnal observation exceeded that of nocturnal observation. Depth distribution of bluefin tuna (Atlantic ; Thunnus thynnus and Pacific; Thunnus orientalis) is known to link to foraging activity (Rooker et al. 27) and to change spatiotemporally according to ambient environment (Wilson et al. 25 for Atlantic bluefin tuna, Kitagawa et al. 2 for Pacific bluefin tuna). This tracking data of #67681 showed that Atlantic bluefin tuna conducted transatlantic movement through various environments changing its diving behavior, with small oscillation movement during residency period and large oscillation movement during long-distance movement period. Stokesbury et al. (27) reported similar change in diving pattern for individual which conducted trans-atlantic movement. This pattern may be correlated with the temperature depth profile in each passing point and/or with bathymetric feature. At present, it is unknown what factor caused the change of its behavior both in horizontally and vertically for this individual. In the next step, we are going to examine the movement pattern more quantitatively and evaluate the association with environmental data in detail. 4. Acknowledgements We appreciate Yukatu Hama, the onboard observer who tagged the PAT to this bluefin tuna, and the crew of the vessel who helped to conduct this research. In addition, we deeply thank Molly Lutcavage and Ben Galuardi who provided much useful suggestions for the tagging method and valuable comments for our tagging research. 5. References Block, B.A, Dewar, H., Blackwell, S.B., Williams, T.D., Prince, E.D., Farwell, C.J., Boustany, A., Teo, S.L.H., Seitz, A., Walli, A., and Fudge, D., 21. Migratory movements, depth preferences, and thermal biology of Atlantic bluefin tuna. Science, 293: Kitagawa, T., Nakata, H., Kimura, S., Itoh, T., Tsuji, S., and Nitta, A., 2. Effect of ambient temperature on the vertical distribution and movement of Pacific bluefin tuna Thunnus thynnus orientalis. Mar. Ecol. Prog. Ser. 26: Lam, Chi H., Nielsen, A., Sibert, J.H., 28 Improving light and temperature based geolocation by unscented Kalman filtering. Fish. Res. 91: Lutcavage, M.E., Brill, R.W., Skomal, G.B., Chase, B.C., and Howey, P.W., Results of pop-up satellite tagging of spawner size class fish in the Gulf of Maine: Do North Atlantic bluefin tuna spawn in the mid-atlantic? Can. J. Fish. Aquqt. Sci., 56: Rooker, J. R., Bremer, J.R.A., Block, B.A., Dewar, H., De Metrio, G.R., Corriero, A., Kraus, R.T., Prince, E.R., Rodríguez-Marín, E., and Secor, D.H., 27. Life history and stock structure of Atlantic bluefin tuna (Thunnus thynnus). Rev. in Fish. Sci. 15: Stokesbury, M.J.W., Cosgrove, R., Boustany, A., Browne, D., Teo, S L.H., O Dor, R.K., Block, B.A., 27. Results of satellite tagging of Atlantic bluefin tuna, Thunnus thynnus, off the coast of Ireland. Hydrobiologia. 582: Wilson, S.G., Lutcavage, M.E., Brill, R.W., Genovese, M.P., Cooper, A.B., and Everly, A.W., 25. Movements of bluefin tuna (Thunnus thynnus) in the northwestern Atlantic Ocean recorded by pop-up satellite archival tags. Mar. Biol. 146:

4 Released point Popped-off point Figure 1. Movement trajectory of # Black solid line with "X" represents light based daily position. Green line represents most probable track which is presented together with confidence bounds (red shaded area) Figure 2.The change of SST(daily) during the period at liberty. "X" represents observed (daily averaged) SST. Blue line represents predicted SST by UKFSST. Green line represents most probable SST by UKFSST 665

5 Depth frequency Percentage (%) m 75-8m 3-35m 25-3m 2-25m 15-2m 1-15m 5-1m -5m Phase Figure 3. The percentage of depth frequency for each class by phase. Percentage (%) Temperature frequency phase1 phase2 phase3 Phase Figure 4. The proportion of temperature frequency for each class by phase. 666

6 (a) (b) Frequency Frequency Depth(m) -2-3 Night Day Depth (m) -2-3 Night Day Phase1 Phase2 (c) Frequency Depth (m) -2-3 Night Day -4-5 Phase3 Figure 5. Depth frequency of night and day for each phase. (a) for phase1, (b) for phase2 and (c) for phase3. 667