By-catch and discards of the european purse seinetuna fishery in the Indian Ocean : estimation and characteristics for the 2003-2007 period

Abstract

By-catch and tuna discards estimation and characteristics for the various species groups are presented for the European purse seine tuna fishery (France and Spain) for the period 2003-2007. Data were collected through French and Spanish observer programs representing a total of 1,958 observed fishing sets. Total by-catch and tuna discards estimation were derived from a stratification based on fishing mode, seasons (quarters) and spatial area. The estimation relied on raising factors based on major commercial tuna catch expressed in tons per 1000 t of tuna landed. Total tuna discards and by-catch was estimated to be about 9,585 t corresponding to 35.5 t per 1000 t of tuna landed. Tuna discards represents 54 % (19.2 t/1000 t) of the total amount, followed by fishes (33.7 %, 12.0 t/1000 t), sharks (10.1, 3.6 t/1000 t), billfishes (1.5 %, 0.5 t/1000 t), and rays (0.7 %, 0.2 t/1000 t). By-catch species composition, main species length and sex structure, and percentage of utilization are also presented. Total by-catch estimates and ratios are compared with those previously published in the literature. The issue raised by the choice of a consistent extrapolation method is finally discussed.