STANDARDIZED CPUE FOR BLUE SHARK AND SHORTFIN MAKO CAUGHT BY THE JAPANESE TUNA LONGLINE FISHERY IN THE ATLANTIC OCEAN

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1 SCRS/2008/149 Collect. Vol. Sci. Pap. ICCAT, 64(5): (2009) STANDARDIZED FOR BLUE SHARK AND SHORTFIN MAKO CAUGHT BY THE JAPANESE TUNA LONGLINE FISHERY IN THE ATLANTIC OCEAN Hiroaki Matsunaga 1 SUMMARY The standardized s for blue shark and shortfin mako caught by the Japanese tuna longline fishery in the Atlantic Ocean were updated using filtered logbook data during for blue shark and for shortfin mako whose reporting rates were more than 80%. Blue shark shows some fluctuations and relatively stable trends during the past three decades for North, South and whole Atlantic stock hypotheses. Shortfin mako indicates decreasing trend until 2001 but after then recovery to the level at beginning is observed. RÉSUMÉ Les standardisées du requin peau bleue et du requin taupe bleue capturés par la pêcherie palangrière thonière du Japon dans l océan Atlantique ont été actualisées à l aide des données filtrées des carnets de bord pendant la période pour le requin peau bleue et pendant la période pour le requin taupe bleue dont les taux de déclaration étaient supérieurs à 80%. La du requin peau bleue dégage quelques fluctuations et 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. La du requin taupe bleue dégage une tendance à la baisse jusqu en 2001, mais l on observe ensuite un rétablissement au niveau du début. RESUMEN Se actualizaron las estandarizadas para la tintorera y el marrajo dientuso capturados por la pesquería atunera de palangre japonés en el Atlántico utilizando datos filtrados de los cuadernos de pesca durante para la tintorera y durante para el marrajo dientuso, cuyas tasas de comunicación eran de más del 80%. La de la tintorera muestra algunas fluctuaciones y tendencias relativamente estables durante las tres décadas pasadas para las hipótesis del Atlántico norte, sur y total. La del marrajo dientuso indica una tendencia descendente hasta 2001 pero posteriormente se observa una recuperación hasta el nivel inicial. KEYWORDS Blue shark, shortfin mako,, longline fishery 1. Introduction The standardized s of blue shark and shortfin mako caught by the Japanese longline fishery in the Atlantic Ocean were reported in previous documents submitted to the ICCAT data preparing meeting for shark stock assessment (Matsunaga 2007a, 2007b) using the filtering method which was introduced by Nakano and Honma (1996) and validated by Nakano and Clarke (2006). In this report, the standardized s of both species in the Atlantic Ocean were updated using the logbook data of the Japanese tuna longline fishery. 1 National Research Institute of Far Seas Fisheries, FRA, Orido, Shimizu-ku, Shizuoka, , Japan. 1677

2 2. Materials and methods The same filtering method of Nakano & Honma (1996) was adopted and data with reporting rates greater than 80% were used in this analysis. This reporting rate was recommended by Nakano and Clarke (2006). The time series of the data extends for 36 years from 1971 to 2006 for blue shark. For much of this period, shark catches were not recorded by species, therefore all sharks are assumed to be blue sharks. That for shortfin mako extends 13 years from 1994 to 2006 for, when shark catches were recorded by species. As described in previous paper (Matsunaga 2007b), some catches of blue shark are supposed to be recorded as those of shortfin mako by mistake especially in 1994 and In the observer data, most of shortfin mako were less than 1 and maximum of them was 1.25 when there was no catch of blue shark. Therefore, data whose of shortfin mako are larger than 1.25 without blue shark catch are considered to be improper and deleted. Standardized (number of sharks caught per 1,000 hooks) were calculated using MIXED and GENMODE procedure of SAS Ver. 9.1 to eliminate biases arising from differences in effort by fishing ground and fishing season. For standardization, was calculated for each operation. The area strata used for the analysis are shown in Figure 1. Numbers of branch line between floats were classified into three categories. The values for both sharks were obtained for three geographical units, i.e. the north, south and overall Atlantic Ocean. The north unit includes Areas 1 to 4; the south includes Areas 5 to 7. The equations for standardizing were as follows: Blue shark: ln( + const) = μ + YR + QT + AR + BR + INTERA+ ε Shortfin mako: E (CATCH) = (Effort)*EXP(INTERCEPT + YR + QT + AR + BR + INTERA) CATCH ~ NB (α, β) where ln: natural logarithm, : nominal (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<), INTERA: any combination of two way interactions, and ε: normal error term. CATCH: nominal catch of sharks in number. Effort: number of hooks. Variable selections were conducted using the stepwise F-test and Chi-square-test (Dobson 1990). Significant level was set at 5 %. 3. Results and discussion Table 1 and Figure 2 show the standardized s and 95% confidence intervals of blue shark for the North, South and whole Atlantic units. The values of ranged around 0.8 to 9.2 and were in the range of values reported by onboard observers in the longline fishery in the Atlantic Ocean (Senba and Nakano 2004). The results from the analysis using Japanese logbook data indicate relatively stable levels with some fluctuations in the North unit, and with some high levels of observed between 1977 and 1980 in the South and whole units. The for the North unit indicates a decreasing trend in , and then shows the mild recovery. Although the trends in differ between North and South, 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. Table 2 and Figure 3 show the year trend of standardized s and 95% confidence intervals of shortfin mako for the North, South and whole Atlantic units. The standardized of shortfin mako in the North Atlantic decreased in 1996 and followed by a mild recovery to the level of beginning. In the South and whole, the decreased gradually until 2001 and recovered to the level of beginning. The results of this analysis suggest that the stock status of shortfin mako has not changed drastically over the past one decade in the high seas area of the Atlantic Ocean. 4. References Nakano, H. and Honma, M., Historical of pelagic sharks caught by the Japanese longline fishery in the Atlantic Ocean. Collect. Vol. Sci. Pap. ICCAT, 46(4): Nakano, H. and Clarke, S., Filtering method for obtaining stock indices by shark species from species-combined logbook data in tuna longline fisheries. Fish. Sci. 72:

3 Matsunaga, H., 2007a, Standardized for blue sharks caught by the Japanese tuna longline fishery in the Atlantic Ocean, Document submitted to the Shark Data Preparing Meeting of ICCAT. Matsunaga, H., 2007b, Standardized for shortfin mako caught by the Japanese tuna longline fishery in the Atlantic Ocean, Document submitted to the Shark Data Preparing Meeting of ICCAT. SAS Institute, SAS/STAT Software, Changes and enhancements. SAS Institute Inc., Cary, NC, USA pp. Senba, Y. and Nakano, H., Summary of species composition and nominal of pelagic sharks based on observer data from the Japanese longline fishery in the Atlantic Ocean from 1995 to Document submitted to the Shark stock assessment meeting of ICCAT. Table 1. Standardized and 95% confidence intervals for blue shark based on the logbook data of Japanese longline fishery in the North, South and whole Atlantic Ocean. North U 95% South W hole

4 Table 2. Standardized and 95% confidence intervals for shortfin mako based on the logbook data of Japanese longline fishery in the North, South and whole Atlantic Ocean. North South U 95% W hole U 95% Figure 1. Area classification used for the analysis. 1680

5 Figure 2. Standardized and 95% confidence intervals for blue shark based on the logbook data of Japanese longline fishery in the Atlantic Ocean (upper: North, middle: South, lower: whole Atlantic). 1681

6 Figure 3. Standardized for shortfin mako based on the logbook data of Japanese longline fishery in the Atlantic Ocean (upper: North, middle: South, lower: whole Atlantic). 1682