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 226848. 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
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 226848, 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 26847.4 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 1.358 (SD=1.5) The monthly CPUE were presented at Table 5. 3.3 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 191-312cm. Figure 2 and 3 presented the size frequency distribution respectively.
Table 1 Monthly hooks and average hooks in the surveyed period Month Fishing days Total hooks Hooks per set December, 27 6 13584 2264 January, 28 3 74432 2481 Febuary, 28 27 7372 276 March, 28 26 6296 2421 April, 28 1 28 28 Total 9 226848 252 Table 2 The catch of major economic species (round weight)(unit: kg) Species ALB BET YFT SWO Catch 7 1744 5857 418 of fish 28 2681 151 143 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 543 1 54 Longfin mako 54 29 17 Blue shark 247 38 66 Bigeye thresher 3694 55 67 Smooth hammerhead 87 7 115 Velvet dogfish 64.4 29 2.2 Bigeye sand tiger 55 1 55 Crocodile shark 71 194 3.7
Total 26847.4 633 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.74.27.68.3.44 Longfin mako.74.134.192.61.128 Blue shark 2.282 2.499.616.7 1.358 Bigeye thresher.294.376.96.243.242 Smooth hammerhead.147.41.3.31 Velvet dogfish.215.55.137.128 Bigeye sand tiger.13.4 Crocodile shark.147.537 1.41.745.855
SCRS/28/156 Figure 1 Survey position 25 2 Mal e, n=127 35 3 Femal e, n=116 25 15 2 1 15 5 1 5 19 21 23 25 27 29 31 33 19 21 23 25 27 29 31 33 Figure 2 Total length frequencies of male and female blue shark. 2 Mal e, n=2 3 Femal e, n=4 2 1 1 15 16 17 18 19 2 15 16 17 18 19 2 Figure 3 Total length frequencies of male and female shortfin mako shark.