SCRS/2011/091 Collect. Vol. Sci. Pap. ICCAT, 68(5): 1915-1921 (2012)

REVIEW OF INFORMATION OF OTHER SHARKS CAUGHT BY JAPANESE LONGLINERS IN THE ATLANTIC

Kotaro Yokawa and Tsubasa Ando1

SUMMARY

In the late-1990s, the Japanese longline logbook system started collecting catch information on oceanic whitetip shark and thresher sharks. In the present study, the logbook information on these sharks was quickly reviewed from the view point of their usefulness for stock assessments. In addition, the information on the sharks catches collected by Japanese longline observers was also reviewed. RÉSUMÉ

À la fin des années 1990, le système japonais de carnet de pêche des palangriers a commencé à recueillir des informations sur les prises de requin océanique et de renard de mer. Dans cette étude, les informations provenant des carnets de pêche sur ces espèces de requin ont été rapidement passées en revue en tenant compte de leur utilité pour l'évaluation des stocks. En outre, les informations sur les prises de requins collectées par les observateurs déployés à bord des palangriers japonais ont également été examinées.

RESUMEN

A finales de los 90, el sistema japonés de cuadernos de pesca del palangre empezó a recopilar información de captura sobre el tiburón oceánico y el tiburón zorro. En este estudio, la información de los cuadernos de pesca sobre estas especies de tiburones fue rápidamente examinada desde el punto de vista de su utilidad en las evaluaciones de stock. Además, se examinó también la información sobre capturas de tiburones recopilada por los observadores del palangre japoneses.

KEYWORDS

Longline, shark

1. Introduction

Japanese log-book system for distant-water longliners had demanded fishers to report the aggregated catch number of all shark species under the category of “sharks”. In 1994, new categories of blue shark, mako sharks, porbeagle and other sharks were developed. In the period between 1998 and 2000, oceanic whitetip shark and thresher sharks were spitted from other sharks. Japanese observers started collect detailed information of shark from distant-water longliners. In the present study, log-book information of oceanic whitetip shark and thresher sharks were briefly reviewed. And also, information of major 10 shark species in the longline observer data were also reviewed.

2. Materials and methods

Log-book data of the catch number of oceanic whitetip shark, thresher sharks as well as other shark were used. For the observe shark data, reported catch number of each shark species or species groups were accumulated, and major 10 sharks and rays were selected by the 10 highest catch species/species group were selected.

1 National Research Institute of Far Seas Fisheries, Japan. 1915 3. Results and discussions

The catches of oceanic white tip shark and thresher sharks were appeared in the log-book of longliners operated in the Atlantic in 1999 and they continuously increased up to the recent years (Figure 1). This would be primarily due to the increase of the reporting ratio of shark (Figure 4). The catch of oceanic whitetip shark is obtained from the tropical to the temperate Atlantic and sizable numbers of catch are occurred in off Cape Town and off Ireland (Figure 2). The catch of thresher sharks is mainly obtained in the off central and southern African counties (Figure 3).

The observer data contains relatively larger number of data for major pelagic sharks and rays (Table 1). The all species/species group, which are reported separately from other sharks in the current log-book system, are appeared in the top 10 sharks and rays. The catch of these top 10 sharks and rays reported by observers were largely fluctuated by year, and this supposed to reflect the number of sets covered by observers for each year as well as the position and season of sets covered by observers.

Most of sharks and rays frequently reported by observers are caught in all major fishing ground of Japanese longliners, while velvet dogfish, crocodile shark and tiger shark are only caught in the tropical and subtropical area (Figures 5 and 6).

The log-book data for oceanic whitetip shark and thresher sharks seem to have enough amounts for some CPUE analysis, although the reliability and representativeness of standardized CPUE should be carefully evaluated. Katsumata et. al. (2011) reported that CPUEs of sharks and rays calculated by Japanese observer data are rather low (less than 0.1 fishes per 1,000 hooks) except for blue shark, porbeagle and pelagic stingray. Because the number of catch of sharks and rays obtained by observers is not so large, usual method of CPUE analysis would not be able to apply on Japanese observer data of most of sharks and rays.

Reference

Katsumata, N., D. Ochi, Y. Inoue, H. Minami and K. Yokawa, 2012, Simulation framework to assess observer coverage for valuable fishes in Japanese observer data. Collect. Vol. Sci. Pap. ICCAT, 67 (in this volume).

1916 Table 1. Reported number of catches of 10 major shark species by Japanese observers in the period between 1997 and 2011. Ocenanic Mako Pelagic Crocodile Velvet Bigeye Tiger Thresher Porbeagle whitetip Blue shark sharks stingray shark dogfish thresher shark sharks shark 1997 493 108 38 0 17 31 6 4 3 4262 1998 204 290 0 0 0 2 179 1 10 2233 1999 16 17 308 0 75 62 0 1 0 553 2000 8 14 28 6 10 14 0 0 0 434 2001 86 30 6 191 106 16 0 8 1 1378 2002 87 61 65 25 71 94 0 6 2 2279 2003 19 3 8 6 20 32 1 1 11 2442 200435667651081902 2005 33 6 6 16 0 1 6 9 0 3004 2006 62 52 5 10 0 3 8 1 8 2707 2007 77 243 16 268 0 6 7 7 22 3093 2008 111 67 101 47 4 21 15 15 22 5141 2009 97 48 199 62 22 33 9 22 5 3459 2010 41 15 20 54 0 1 7 19 3 3677 2011 12 3 11 30 0 1 0 11 0 566

12000 other sharks

10000 thresher sharks

8000 oceanic whitetip

catch shark

of 6000

4000 number

2000

0 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 year Figure 1. Catch number of oceanic whitetip shark, thresher sharks and other sharks reported by log-book system of Japanese distant-water longliners. Catch number of oceanic whitetip sharks and thresher sharks were requested to report in 1998 -2000. Values in 2010 are preliminary.

1917

Figure 2. Distribution of catch number of oceanic whitetip shark reported by the logbook of Japanese longliners in the Atlantic in the period between 1999 and 2009.

1918

Figure 3. Distribution of catch number of thresher sharks reported by the logbook of Japanese longliners in the Atlantic in the period between 1999 and 2009.

1919 0.8 0.7 ratio of hooks 0.6 ratio of sets 0.5 total

to 0.4

0.3 ratio 0.2 0.1 0

year

Figure 4. Ratio of effort (hooks and sets) with shark catches to the total of the logbook in the period between 1995 and 2010. Values in 2010 are preliminary.

Figure 5. Distribution of catches of blue sharks (left top), pelagic stingray (left middle), porbeagle (left bottom), mako sharks (right top), crocodile shark (right middle) and velvet dogfish (right bottom) reported by longline observers in 1997-2011. Close circle shows the position with relatively higher catch ratio than others shown by open circle.

1920

Figure 6. Distribution of catches of bigeye thresher (left top), thresher sharks (left bottom, species not identified), tiger shark (right top), and velvet dogfish (oceanic whitetip shark) reported by longline observers in 1997-2011. Close circle shows the position with relatively higher catch ratio than others shown by open circle.

1921