Evaluation of sampling gear for demersal resource surveys

Abstract

The three demersal trawls evaluated were 38 m HSDT-II, indigenously developed by CIFT for deep sea fishing in Indian EEZ; and two imported designs, viz., 45.6 m Expo model demersal trawl and 50 m fish trawl operated from vessels of FSI and IFP, respectively. Vertical opening at trawl mouth was heighest for 50 m fish trawl (3.2 m), followed by Expo model demersal trawl (2.5 m) and 38 m HSDT-II (2.2 m), due to differences in overall dimensions and design features. Estimate of horizontal opening between otter boards was highest for 38 m HSDT-II probably due to low drag of the gear, followed by 45.6 m and 50 m trawls. Lowest catch per unit effort obtained by 38 m HSDT_II is presumably due to smaller dimensions of the gear, larger codend mesh size and difference in ground ring, in addition to chance factors. However, 38 m HSDT-II scores on several features desirable in demersal sampling gear such as simplicity in design and construction, ease of operation; lower twine surface area and drag; and ground ring suitable for wider range of bottom conditions. Modifications to make it more effective while sampling for crustaceans and small sized finish components are described.