Fish Production and Energy Requirement during Demersal and Aimed Midwater Trawling by Intermediate Range Freezer Trawler

Abstract

This paper deals with the fish production and relative energy consumption in demersal and midwater trawling based on data derived from cruises of Intermediate range freezer trawler that operated in Indian waters during 1993-94. The trawler has length overall of 62.2 m, gross registered tonnage of 1898 and installed engine power of 2400 hp. Operations were conducted between 14 degree and 22 degree N lat., off west cost of India, within a depth range of 31 and 125 m, using 47.5 m four-seam bottom trawl rigged with bobbin gear and 70.0 m mid-water trawl. The present investigations have shown that significant improvements in landings were obtained during aimed midwater trawling, off west coast of India. The mean daily landings rose from an average of 5.66 t, during bottom trawling to 22.84 t, during midwater trawling, realising over 300% improvement in the landings that manifested in a significant reduction in the consumption of fuel per unit volume of fish landed by midwater trawling. Overall fuel consumption per kg fish landed by bottom trawling and midwater trawling worked to be 1.34 and 0.33 kg, showing a four-fold difference. The difference in daily fuel expenditure per unit volume of fish between bottom and aimed mid-water trawling was found to be highly significant statistically. As there is intense concentration of effort in the bottom trawl fisheries, it could be advantageous from the resource management perspective and also from the energy conservation point of view, to encourage diversification to midwater trawling, in a controlled manner without compromising on sustainability of resources. Stern trawler does not require any large-scale modifications in structure or deck layout, for undertaking midwater trawling. However, the vessel must be large enough, highly manoeuvrable and sufficiently powered to tow a large mouthed midwater trawl at speeds exceeding 4.5 knots; should be equipped with acoustic fish detection (sonar and echosounder) and trawl monitoring systems; and in addition, must have provision for handling and preserving large volume landings.