Shark bycatch observation in the ICCAT waters by. Chineses longline observer in 2007

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1 Shark bycatch observation in the ICCAT waters by Chineses longline observer in 27 Xiao-jie DAI 1 and Run-lin Jiang SUMMARY The paerr presented the shark data collected by Chinese longline fishing observer during Decmber 27 to April 28, with the total 9 fishing days and total hooks Survey areas covered 5 37 N~12 1 N, 29 W~36 51 W. There are 8 species shark in the bycatch. Blue shark was most abundant, accounting for the 76.2% in shark weight. The monthly CPUE of shark were reported and blue shark sex ratio and size frequency distribution were also presented. Key words: Shark bycatch, observer, tropical Atlantic ocean.. 1. Introduction Sharks are top predators in the oceanic ecosystem and are very important species. Great concerns are made by ICCAT and other Regional Fishery Management Organiztion. ICCAT has made pilot research for the blue shark and shortfin mako stock assessment in 28, which shall greatly contribute to the scientific-based management. China has conducted observer programme annually in order to collect more 1 Shanghai Ocean University, 999 Huchenghe Road, Lingang New Town, Shanghai 2136, P. R. China

2 detailed shark information and hope estimate accurate shark catch information. 2. Material and Methods 2.1 Survey periods and survey vessel The scientific observer survey was conducted during Decmber 27 to April 28, with total 9 fishing days(sets). The survey vessels were Chinese longliers Jingfeng No.3 (Decmber 27 to January 28) and Jingfeng No.4(Febuary 28 to April 28), with GRT 619t. 2.2 Survey areas Survey areas covered 5 37 N~12 1 N,29 W~36 51 W,belonging to the high seas of tropical Atlantic Ocean (Figure 1). 2.3 Shark sampling and measurements All the shark species were identified by sex. Total length and round weight of sharks was measured by observers. 3. Results 3.1 Catch and shark bycatch information During observer survey, total hooks were deployed as , with average 252 hooks per set(table 1). The targeted species was bigeye tuna, with the total catch 1744 kg (Table 2). There were 8 shark species appeared in the catch (Table 3). It is noted that there was no oceanic whitetip shark and it probably connected with deep longline set. The total shark catch were kg and blue shark was most abundant species, accounting for about 76.2% in weight(table 4). 3.2 CPUE The CUPE of different shark species fluctuated between.4 and 1.358, of which the blue shark CPUE was highest. The CUPE of blue shark was (SD=1.5) The monthly CPUE were presented at Table Blue shark sex ratio and length frequency The total blue shark was 38 individual, and 243 were identified by sex. Male was127 and female 116. The total length range of blue shark were cm. Figure 2 and 3 presented the size frequency distribution respectively.

3 Table 1 Monthly hooks and average hooks in the surveyed period Month Fishing days Total hooks Hooks per set December, January, Febuary, March, April, Total Table 2 The catch of major economic species (round weight)(unit: kg) Species ALB BET YFT SWO Catch of fish Table.3 The list of shark species by catch longline fishing by observer sampling Name Scientific name Shortfin mako Isurus oxyrinchus Longfin mako Isurus paucus Blue shark Prionace glauca Bigeye thresher Alopias superciliosus Smooth hammerhead Sphyrna zygaena Velvet dogfish Zameus squamulosus Bigeye sand tiger Odontaspis noronhai Crocodile shark Pseudocarcharias kamoharai Table 4 Catch of sharks by observer survey (round weight)(unit: kg) Species Weight No. Average weight Shortfin mako Longfin mako Blue shark Bigeye thresher Smooth hammerhead Velvet dogfish Bigeye sand tiger Crocodile shark

4 Total Table 5 The shark CPUE by Chinese longline fishing in the high sea of tropical Atlantic Ocean Unit: No. per 1 hooks Species Monthly CPUE Dec 27 Jan 28 Feb 28 Mar 28 Average Shortfin mako Longfin mako Blue shark Bigeye thresher Smooth hammerhead Velvet dogfish Bigeye sand tiger.13.4 Crocodile shark

5 SCRS/28/156 Figure 1 Survey position 25 2 Mal e, n= Femal e, n= Figure 2 Total length frequencies of male and female blue shark. 2 Mal e, n=2 3 Femal e, n= Figure 3 Total length frequencies of male and female shortfin mako shark.