NOTE ON THE STRONG 2003 YEAR-CLASS THAT APPEARED IN THE ATLANTIC BLUEFIN FISHERIES

Transcription

1 SCRS/2012/101 Collect. Vol. Sci. Pap. ICCAT, 69(1): (2013) NOTE ON THE STRONG 2003 YEAR-CLASS THAT APPEARED IN THE ATLANTIC BLUEFIN FISHERIES Ziro Suzuki 1, Ai Kimoto 1 and Osamu Sakai 1 SUMMARY It was stated in the stock assessment of the Atlantic bluefin tuna in 2010 that the 2003 year-class could be a strong year class that originated from the West Atlantic stock. This year-class appeared in the catch of the Japanese longline fishery that operated in the East Atlantic as a clear indication of the strong year-class but it does not seem so strong and not in a consistent way in the catches of the fishery in the West Atlantic. The concurrent appearance of this year-class is identified in some of well documented important fisheries in the East Atlantic and Mediterranean fisheries such as the Spanish baitboat fishery in the Bay of Biscay and the Sardinian trap fishery in Italy. Although the 2003 year-class could be a strong year-class that originated both in the West and East Atlantic, this year-class seems to be more dominant and consistently appears in the eastern Atlantic stock. Full analyses for all other important fisheries in the entire Atlantic and Mediterranean Sea are required to determine the relative strength of this year-class in the West and East stocks. RÉSUMÉ L'évaluation du stock de thon rouge de l'atlantique, menée en 2010, affirmait que la classe annuelle de 2003 pourrait être une forte cohorte qui provenait du stock de l'atlantique Ouest. Cette classe annuelle est apparue dans les captures de la pêcherie palangrière japonaise qui opérait dans l'atlantique Est comme une claire indication de la force de la cohorte, mais elle ne semble pas aussi forte et pas d'une manière cohérente dans les prises de la pêcherie de l'atlantique Ouest. L'apparition concurrente de cette classe annuelle est identifiée dans certaines pêcheries importantes bien documentées de l'atlantique Est et de la Méditerranée, comme la pêcherie palangrière espagnole qui opère dans le golfe de Gascogne et la pêcherie de madragues de la Sardaigne en Italie. Même si la classe annuelle de 2003 pourrait être une forte cohorte qui provenait à la fois de l'atlantique Ouest et de l'atlantique Est, cette classe annuelle semble être plus dominante et apparaît invariablement dans le stock de l Atlantique Est. Il est nécessaire de réaliser des analyses complètes de toutes les pêcheries importantes qui opèrent dans l'ensemble de l'océan Atlantique et de la mer Méditerranée afin de déterminer la force relative de cette classe annuelle dans les stocks de l'ouest et de l'est. RESUMEN En la evaluación del stock de atún rojo del Atlántico de 2010 se afirmó que la clase anual de 2003 podría ser una case anual fuerte originaria del stock del Atlántico occidental. Esta clase anual apareció en la captura de la pesquería de palangre japonesa que operó en el Atlántico este como un indicio claro de la fuerte clase anual, pero no parece ser tan fuerte y no es coherente con las capturas de la pesquería en el Atlántico occidental. La presencia simultánea de esta clase anual está identificada en algunas importantes pesquerías bien documentados del Atlántico Este y Mediterráneo, como la pesquería de cebo vivo española, en el golfo de Vizcaya, y la pesquería de almadraba sarda, en Italia. Aunque la clase anual de 2003 podría ser una fuerte clase original procedente tanto del Atlántico este como del Atlántico oeste, esta clase anual parece más predominante y aparece más frecuentemente en el stock del Atlántico oriental. Se requieren análisis completos de otras importantes pesquerías en todo el Atlántico y Mediterráneo para determinar la fuerza relativa de esta clase anual en los stocks del Atlántico oriental y del Atlántico occidental. KEYWORDS Atlantic bluefin, 2003 year class, Japanese longline fishery, Spanish baitboat fishery, Sardinian trap fishery 1 National Research Institute of Far Seas Fisheries-NRIFSF, 5-7-1, Shimizu, Shizuoka, , Japan, zsuzuki@affrc.go.jp, aikimoto@affrc.go.jp, sakaios@fra.affrc.go.jp 229

2 Introduction The latest SCRS species report on bluefin tuna (Anon. 2012) stated for west Atlantic stock that The strong 2003 year class has contributed to stock productivity such that biomass has been increasing in recent years while for the east Atlantic stock, the same report did not mention specifically to the 2003 year class. As the data for additional 2 years are accumulated, more information about this year class becomes available. The recent data provided by the Japanese longline fishery shows the 2003 year class now is prominent in the bluefin catches of the east Atlantic but does not seems to be as conspicuous and consistent in the time series as that in the west Atlantic. We collected the relevant data and papers about the 2003 year class available at hand and tried to trace the 2003 year class in various bluefin fisheries in the Atlantic. Fisheries referred with respect to 2003 year class Japanese longline fishery Relevant information about 2003 year class appeared in the Japanese longline fishery is summarized as follows. Retrospectively, the 2003 year class firstly could be recognized as potential strong year class in the length composition of the catch of the Japanese longline fishery operating in the west Atlantic in 2007 but not so remarkable for the following 2008 and 2009 (Figure 1 reproduced from Figure 11 of Kimoto et al. 2011). On the contrary, potential 2003 year class appeared noticeable in east Atlantic in 2008 and 2009 but not so noticeable in Latest analysis of size of Atlantic bluefin caught by the Japanese longline fishery was made based on weight measured by 1 kg, first, conversion to corresponding length using weight-length keys available in the ICCAT web-site, second, conversion to age (Restrepo et al. (2009) for the west Atlantic and Cort (1991) for the east Atlantic). Date of birth was set in May and July for the west and east Atlantic, respectively. Figure 2 shows more clearly the 2003 year class is outstandingly strong. However, the 2003 year class tends to be more consistently dominant in the east Atlantic catch but not necessarily so in the west Atlantic catch is compared to the east counterpart. In addition, for the Japanese longline fishery in the east Atlantic, the year classes following to the 2003 year class do not seem to be strong. Spanish baitboat fishery in Bay of Biscay Several candidates of the strong year classes are indicated from abundance indices by age for this fishery and the 2003 year class is among the several candidates of the strong year class (Rodriguez-Marin et al., 2011). However, the relative strength of the 2003 year class is not outstandingly high compared with other prominent year classes. Sardinian trap fishery in Italy Addis et al. (2012) showed time series of age composition captured by Sardinian traps from Figure 3 of Addis et al. (2012) paper clearly indicated the appearance of 2003 year class and as a consequence of entrance of this year class, average weight decreased significantly and standardized CPUE increased. This paper mentioned possibility of occurrences of relatively strong year classes, 2004 and 2005 year classes but less than the 2003 year class, followed after 2003 year class. Summary remarks There are several other fisheries relevant to be referred such as trap fisheries of Spain, Morocco and Portugal. There appears to be some changes in recent length composition of the Spanish trap, i.e., a small fraction of catch that including the 2003 year class appeared (Cort and Martínez, 2010) and a significant increase in the catches of the Portuguese traps that catch substantial amount of bluefin less than 200 kg (Neves dos Santos and Coelho, 2011), that might be indication of small adult of the 2003 recruiting to these fisheries. However, no such change is evident for Moroccan trap fishery (Idrissi and Abid, 2011) although the overall average size of gigantic bluefin is on decrease as Spanish and Portuguese trap cases. As the Moroccan and Spanish traps catch very large fish over 200 kg, it is expected increase of CPUE in these traps within several years when the 2003 year class attained this size. Also, no change is observed in Tunisian fisheries that take mainly juvenile bluefin tuna 230

3 (Hattour, 2009). Unfortunately, we could not find out references with respect to the 2003 year class in French, Turkish, Italian, Spanish and Croatian purse seine fisheries. Therefore, thorough investigation of references for these purse seine catch is highly desirable to be done if the documentations for these fisheries on changes in length composition are available. There is little specific information available about potential 2003 year class in the west Atlantic other than the Japanese longline analysis. Although it is noted that the 2003 year class is a strong year class in the CPUE time series of the US RR (Rod and Reel) young age (Anon. 2012), the progression of this series does not look like to be an outstandingly strong year class. The potential 2003 year class recognized first in the west Atlantic but it is probably a fraction of east Atlantic stock as most of juvenile bluefin in the west Atlantic are composed of immigrants from the east Atlantic (Rooker et al. 2008). However, this year class, originated in the west Atlantic concurrently with the east Atlantic counterpart, might also be a strong year class, To verify the relative strength of year class, it is important that the mixing rate estimates by stable isotopes are expanded to cover a wider time/area/size stratum supplemented by comparison with historical archival of otoliths (Secor et al. 2012). The Japanese longline operated in the west Atlantic catches bluefin tuna both small (less than 150 cm) and larger fish with rather unstable time and area coverage year by year. On the other hand, the fishing of the Japanese longline fishery in the east Atlantic catches mostly large fish and time and area coverage of the fishing ground is more stable compared to the west Atlantic fishing ground. This difference may mask to show potential strong 2003 class occurred in the west Atlantic. These fisheries indicators are qualitative and may not reflect the actual changes in the stocks. In addition, it should be noted that there has been shrinkage of time and area data coverage of the Japanese longline fishery, serious lack of reliable size information of bluefin taken by purse seine fisheries in the Mediterranean Sea and lack of continuity in CPUE time series for most of Atlantic bluefin fisheries due to intensification of regulatory measures. Analyses for all other important fisheries in the whole Atlantic and Mediterranean Sea are required to determine relative strength of this year class in the west and east stocks. Although the inference made in this note should be kept pending until full stock assessment using updated data is made the full assessment also is largely influenced by these changes in the bluefin fisheries. In this regard, it is urgently needed to obtain much more information about mixing rates of the two stocks so that the fisheries statistics can be sorted out by stock. References Addis, P., Secci, M., Locci, I., Cau, A., Sabatini, A., 2012, Analysis of Atlantic bluefin tuna catches from the last Tonnara in the Mediterranean Sea: , Fish. Res. Volumes , September 2012, pp Anon., 2012, Report for biennial period, , Part II (2011) - Vol. 2, English version ICCAT SCRS, 269 pp. Cort, J. L. 1991, Age and growth of the bluefin tuna Thunnus thynnus (L.) of the Northeast Atlantic. Collect. Vol. Sci. Pap. ICCAT, 35: Cort, J. L., Martínez, D., 2010, Possible effects of the bluefin tuna (Thunnus thynnus) Recovery plan in some Spanish fisheries. Collect. Vol. Sci. Pap. ICCAT, 65(3): Hattour, A., 2009, Repartition demographique du thon rouge engraisse dans les fermes tunisiennes pendant les campagnes 2005 a Collect. Vol. Sci. Pap. ICCAT, 64(2): Idrissi, M., Abid N., 2011, The Moroccan Atlantic traps: comparison between the estimation of the size composition of bluefin tuna catches from the average weight of fish and biological scraps, Collect. Vol. Sci. Pap. ICCAT, 66(2): Kimoto A., Itoh, T., Miyake, M., 2011, updated standardized bluefin CPUE from the Japanese longline fishery in the Atlantic up to Collect. Vol. Sci. Pap. ICCAT, 66(2): Neves dos Santos, M., Coelho, R., 2011, Bluefin tuna catches in the Algarve tuna trap (southern Portugal, ne Atlantic): comments on the recent management regulations in the Mediterranean Sea. Collect. Vol. Sci. Pap. ICCAT, 66(2): Restrepo, V.R., Diaz, G. A., Walter, J. F., Nielson, J., Campana, S., Secor, D. and Wingate, R. L. 2009, Updated estimate of the growth of western Atlantic bluefin tuna. Aquat. Living Resour. 23, (2010). 231

4 Rodriguez-Marin, E., Ortiz De Urbina, J. M., Ortiz, M., Ruiz, M., Perez, B., 2011, Updated nominal catch rates of Atlantic bluefin tuna caught by the Spanish baitboat fishery in the Bay of Biscay (eastern Atlantic). effect of current regulations. Collect. Vol. Sci. Pap. ICCAT, 66(2): Rooker, J. R., Secor, D.H., De Metrio, G., Schloesser, R., Block, B.A., Neilson, J. D., 2008, Natal homing and connectivity in Atlantic bluefin tuna populations. Science 322, Secor, D. H., Gahagan, B., Rooker, J. R., 2012, Atlantic bluefin tuna population assignment based on otolith stable isotopes: the 2003 year-class within the U.S. North Carolina recreational fishery. Collect. Vol. Sci. Pap. ICCAT, 68(1):

5 Figure 1. Fork length frequencies from 2007 to 2009 measured by observed program and on board size measurement program in the west Atlantic (west of 45 W) and the east Atlantic (east of 45 W). Cited from Kimoto et al from their Figure 11. Red arrows indicate conspicuous appearance of the strong 2003 year class in some years. 233

6 Figure 2. Catch at age compositions of bluefin tuna for the west and east Atlantic (divided by 45W). Figure 3. Age composition of bluefin caught by Sardinian traps (cited from Figure 3 of Addis et al. (2012)) 234