STANDARDIZED CPUE FOR BLUE SHARKS CAUGHT BY THE JAPANESE LONGLINE FISHERY IN THE ATLANTIC OCEAN,

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1 SCRS/2004/119 Col. Vol. Sci. Pap. ICCAT, 58(3): (2005) STANDARDIZED CPUE FOR BLUE SHARKS CAUGHT BY THE JAPANESE LONGLINE FISHERY IN THE ATLANTIC OCEAN, Hideki Nakano, Shelley Clarke 1 SUMMARY The standardized catch per unit effort (CPUE) for blue shark caught by Japanese longline fishery in the Atlantic Ocean was updated using logbook data from filtered such that only those cruises which reported catching at least one shark in at least 70% of all sets were retained. For most of this period, shark catches were not classified, therefore all sharks are assumed to be blue sharks. Blue shark CPUEs indicate relatively stable trends during the past three decades for North, South and whole Atlantic stock hypotheses. RÉSUMÉ La capture par unité d effort (CPUE) standardisée du requin peau bleue capturé par la pêcherie palangrière japonaise dans l océan Atlantique a été actualisée à l aide des données des carnets de bord de filtrées de telle manière que seules les sorties où il a été déclaré une capture d au moins un requin dans au moins 70% de toutes les opérations ont été retenues. Pour la plupart de cette période, les prises de requins n ont pas été classifiées, c est pourquoi on postule que tous les requins sont des requins peaux bleues. Les CPUE des requins peaux bleues indiquent des tendances relativement stables au cours des trois dernières décennies pour les hypothèses des stocks de l Atlantique Nord, Sud et de l ensemble de l Atlantique. RESUMEN Se ha actualizado la captura por unidad de esfuerzo (CPUE) estandarizada para la tintorera capturada por la pesquería japonesa de palangre en el Océano Atlántico utilizando datos de los cuadernos de pesca desde 1971 hasta 2003 filtrados de tal forma que sólo se han mantenido aquellas campañas en las que se declaró la captura de al menos un tiburón en al menos el 70% de todos los lances. Para la mayoría de este periodo, las capturas de tiburones no están clasificadas, por lo que se asume que todos los tiburones son tintoreras. Las CPUE de la tintorera indican tendencias relativamente estables durante las tres décadas pasadas para las hipótesis de stock del Atlántico norte, sur y total. KEYWORDS High seas fisheries, Long line, Tuna fisheries, Time series analysis, Catch/effort, Blue shark 1 National Research Institute of Far Seas Fisheries, FRA, Japan, Orido, Shimizu-Ku, Shizuoka, SHIZUOKA, , Japan hnakano@affrc.go.jp 1127

2 1. Introduction Nakano and Honma (1996) analyzed the CPUE of pelagic sharks in the Atlantic Ocean using Japanese longline logbook data filtered by shark reporting category, e.g. the ratio of sets in which sharks were caught relative to the total number of sets in a cruise. Shiode and Nakano (2001) examined shark species composition and CPUE by reporting category through comparison to records of shark catch by Japanese observers and concluded that CPUE calculated from filtered logbook data could be used as an abundance index of the species. This was because sharks records in the filtered logbook data since the implementation of species-specific reporting requirements are composed of more than 86% of blue shark catch (in number) and the CPUE calculated from the filtered logbook data was in the range of variation observed in the CPUE as recorded by onboard observers. The standardized CPUE of pelagic sharks caught by the Japanese longline fishery in the Atlantic Ocean was introduced in previous reports submitted to the ICCAT Sub-committee on By-catches (Nakano and Honma 1996, Nakano 1998, Nakano 1999, Nakano 2001). Since the Japanese longline fishery has widely covered the high seas area of the Atlantic Oceans, its fishery statistics should be one of the most valuable means of describing the stock status of pelagic sharks. Since there is international concern over the conservation of elasmobranch species, it is useful to examine recent trends in the stock status of blue shark using the most recent logbook data from tuna fisheries. This paper estimates the standardized CPUEs of blue shark in the Atlantic Ocean using the logbook data of the Japanese longline fishery from 1971 to Materials and methods Data from records in which the reporting rate was greater than or equal to 70% were used in this analysis. The time series of the data extends for 33 years from 1971 to 2003, but data for 2003 is provisional. Standardized CPUE (number of sharks caught per 1,000 hooks) were calculated using a generalized linear model (SAS Ver. 6.12, MIXED procedure (SAS Institute 1996)) to eliminate biases arising from differences in effort by fishing ground and fishing season. Although the MIXED procedure can handle random-effect parameters, only fixed-effect parameters were used, therefore the results from the MIXED procedure will agree with those from the GLM procedure. The MIXED procedure was used because it produces several useful information criteria values. For standardization, CPUE was calculated for each set within a cruise. The area strata used for the analysis are shown in Figure 1. Numbers of branch line between floats were classified into three categories. The CPUE values for blue sharks were obtained for same three geographical units used in the previous report, i.e. the north, south and overall Atlantic Ocean. The north unit includes Areas 1 to 5; the south includes Areas 6 to 8. The equation for standardizing CPUE was as follows: ln(cpue + const) = μ + YR + QT + AR + br + INTER + ε where ln: natural logarithm, CPUE: nominal CPUE (catch in number per 1,000 hooks), const : 1/10 of overall mean, μ: overall mean, YR: effect of year, QT: effect of quarter, AR: effect of area, br: branch line criteria (number of branch lines between buoys; <9, 9-14, 14<), INTER: any combination of two way interactions, andε: normal error term. The same effects selected for previous report including interaction terms were used for this analysis. The interactions included for the models were QT*AREA and QT*br for the North, South and overall Atlantic stock hypothesis. 3. Results and discussion Table 1 shows number of observations in each year by geographical unit, respectively. Type III analysis revealed that all main effects and modeled interactions of the selected models were significant (Table 2). Figure 2 shows the standardized CPUEs for the North, South and whole Atlantic units. The values of CPUE ranged between 1.0 and 7.0 and were in the range of CPUE values reported by onboard observers in the longline fishery. The reported CPUE of pelagic sharks (number of caught per 1,000 hooks) in the literature ranges from 1.31 to 38.8 (Strasburg 1958, Lopez et al. 1979, Witzell 1985, Hazin et al. 1990, Taniuchi 1990, Bonfil 1994). The results from the Japanese logbook data indicate relatively stable levels with small fluctuations in the North 1128

3 unit, and some high levels of CPUE observed between 1976 and 1981 in the South and overall units. The CPUE for the North unit indicates a decreasing trend in , then shows staying around 1.0. Regarding the South, it shows decreasing trend from Although the trends in CPUE differ between North and South, fluctuations in CPUE were small relative to those observed in tunas and billfishes caught by Atlantic fisheries (ICCAT 2003). Overall, the results of this analysis suggest that the stock status of blue sharks has not changed drastically over the past three decades in the high seas area of the Atlantic Ocean. The sharks caught in Atlantic high seas are mainly consist of blue shark (Strasburg 1958, Hazin et al. 1990, Bonfil 1994, Matsunaga and Nakano 1996, Nakano and Honma 1996) and as concluded above the stock status of blue sharks in the Atlantic Ocean appears not to have greatly changed during the study period. However, there is little information relating to the long-term stock status for other pelagic shark species which inhabits the high seas area. It is necessary to conduct further onboard research activities, such as observer programs, to examine the population dynamics for each species. References BONFIL, R Overview of world elasmobranch fisheries. FAO fisheries technical paper 341, pp HAZIN, F.H., A.A. Couto, K.Kihara, K. Otsuka, and M. Ishino Distribution and abundance of pelagic sharks in the south-western equatorial Atlantic. J. Tokyo Univ. Fish. 77(1): ICCAT Report for biennial period, , part I (2002) Vol. 2, Madrid, Spain. 216pp. LOPEZ, A.M., D.B. McClellan, A.R. Bertolino and M.D. Lange The Japanese longline fishery in thegulf of Mexico, Mar. Fish. Rev. 41(10): MATSUNAGA, H and H. Nakano CPUE trend and species composition of pelagic shark caught byjapanese research and training vessels in the Pacific Ocean. Information Paper submitted to the CITES Animals Committee held at Pruhonice, Czech Republic, NAKANO, H Standardized CPUE for pelagic shark caught by the Japanese longline fishery in the Atlantic Ocean. ICCAT CVSP Vol. XLVIII (3): NAKANO, H Updated standardized CPUE for pelagic sharks caught by the Japanese longline fishery in the Atlantic Ocean. ICCAT CVSP Vol. LI 2000, SCRS/99/41 8pp. NAKANO, H Standardized CPUE for blue sharks caught by Japanese longline fishery in the Atlantic Ocean. ICCAT CVSP Vol. LIV 2002, SCRS/2001/083 12pp. NAKANO, H. and M. Honma Historical CPUE of pelagic sharks caught by the Japanese longlinefishery in the Atlantic Ocean. ICCAT CVSP Vol. XLVI (4): SAS Institute SAS/STAT Software, Changes and enhancements. SAS Institute Inc., Cary, NC, USA. 1094pp. SHIODE, D. and H. Nakano Verification of shark catch data of the logbook records in Japanese longline fishery in comparison with the observer reports. Document submitted to the Shark data preparation meeting of ICCAT. STRASBURG, D.W Distribution, abundance, and habits of pelagic sharks in the central Pacific Ocean. Fish. Bull. U.S. Fish. Wildlife Serv. 58: TANIUCHI, T The role of Elasmobranchs in Japanese fisheries. NOAA Tech. Rep. NMFS 90: WITZELL, W.N The incidental capture of sharks in the Atlantic United States Fishery Conservation Zone by the Japanese tuna longline fleet. NOAA Tech. Rep. NMFS 31:

4 Table 1. Number of observations which has more than 70% reporting category by geographical unit in each year. Year North South Overall Total

5 Table 2. Outputs of Type III analysis for the models selected in each unit. North Atlantic: Test of Fixed Effects Type III Type III Effect NDF DDF Chi-Sq F Value Pr > ChiSq Pr > F Ord F YR E <.0001 < QT E <.0001 < area E <.0001 < br E <.0001 < QT*area E <.0001 < QT*br E <.0001 < South Atlantic: Test of Fixed Effects Type III Type III Effect NDF DDF Chi-Sq F Value Pr > ChiSq Pr > F Ord F YR E <.0001 < QT E <.0001 < area E <.0001 < br E <.0001 < QT*area E <.0001 < QT*br E <.0001 < Overall Atlantic: Test of Fixed Effects Type III Type III Effect NDF DDF Chi-Sq F Value Pr > ChiSq Pr > F Ord F YR E <.0001 < QT E <.0001 < area E <.0001 < br E <.0001 < QT*area E <.0001 < QT*br E <.0001 < NDF is the numerator degrees of freedom, and DDF is the denominator degrees of freedom. 1131

6 Table 3. Annual, standardized CPUE from the models selected in each unit. Year CPUE Lower Upper CPUE Lower Upper CPUE Lower Upper

7 Figure 1. Area classification used for the analysis. 1133

8 4 Blue shark standardized CPUE in the north Altantic Standardized CPUE Year CPUE upper 95% lower 95% 7 Blue shark standardized CPUE in the south Altantic 6 Standardized CPUE Year CPUE upper 95% lower 95% 5 Blue shark standardized CPUE in the all over Altantic Standardized CPUE Year CPUE Upper 95% Lower 95% Figure 2. Standardized shark CPUE and 95% confidence intervals based on the logbook data of Japanese longline fishery in the Atlantic Ocean. 1134