Vertical distribution of blue Shark (Prionace glauca) in The Indian Ocean

Fathur Rochman,Roy Kurniawan,Arief Wujdi,Gussasta Levi Arnenda,E.S Kartamihardja,C.P.H Simanjuntak,D.F Mokodongan,A Collins,E Setyobudi,S.M Bergmann,T Peristiwady,Alimuddin Alimuddin,Djumanto Djumanto,P.G Sasmita,N Hubert,S.B Andi Omar

doi:10.1051/e3sconf/202132201009

Abstract

Each fish species tends to choose a suitable environment suitable for its survival and reproduction horizontally and vertically. Blue shark (Prionace glauca) is the dominant catch of pelagic sharks by-catch in the Eastern Indian Ocean longline tuna fishery, with about 70% of the total sharks caught in this fisheries. This study aims to provide the information and the vertical analysis distribution of blue sharks based on temperature and depth in the Indian Ocean. The scientific observer collected 2,951 set-by-set longline fishing data based on Research Institute For Tuna Fisheries (RITF) from January 2006 to December 2018, on which the present analysis was made. The mini logger was used to measure the vertical distribution of blue sharks in the longline fisheries. This result indicated that blue shark was caught between 75.18-445.46 m depth, with 84% of which live at thermocline area (70-300 m depth), and 16% lived in underlayer area (>300 m depth). Blue sharks distributed in the underlayer area have a larger body size than those in the thermocline area with a size >180 cmFL compared to 50-170 cmFL in the thermocline area.

Highlights

The blue shark is a highly migratory species
The depth and temperature of the waters significantly affect the vertical distribution of fish and the vertical distribution of blue sharks
This research indicated that the blue shark was caught at a depth of 75.18 m to 445.46 m, with temperatures ranging from 90C to 260C (Figure 2). 84% of blue sharks caught in the thermocline area with a depth of 70 to 300 m, while 16% are distributed slightly below the thermocline area up to a maximum 445.46 m depth. (Table 1)

Summary

Introduction

The blue shark is a highly migratory species. Its range widely across many national boundaries and spending its time up to 92% in high seas makes it challenging to control and monitor [1]–[3]. The blue shark is by-catch species in longline tuna fisheries caught together with tuna species [3]–[5]. As a by-cath species in longline activity, the capture of blue sharks is unavoidable. [3], [8] reported that the discharged rate of blue sharks of the U.S and Canadian tuna fisheries approached 100% due to the non-commercial value of this species in North America. This information is a significant problem, and the current state of sharks includes those faced by the blue shark species in the Indian Ocean where this study was conducted

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Results