This study was conducted to fi nd out the relations between trawling speed and vertical opening of trawl net. The study uses a trawl model to perform a test in a flume tank at various trawling speeds, from m/s to m/s, this is equivalent knots to knots in the field for full-scale net. | Journal of Fisheries science and Technology No. 4 - 2018 IMPACT OF TRAWLING SPEED ON VERTICAL OPENING OF TRAWL NET BY MODELLING METHOD Nguyen Huu Thanh¹ Received: ; Revised: ; Accepted: ABSTRACT This study was conducted to find out the relations between trawling speed and vertical opening of trawl net. The study uses a trawl model to perform a test in a flume tank at various trawling speeds, from m/s to m/s, this is equivalent knots to knots in the field for full-scale net. The results show that the vertical opening of the net mouth decreases as the trawling speed increases, the vertical opening was reduced by more than 32% as the speed increased from knots to knots. The regression results show that there is an approximate relationship between trawling speed and vertical opening with a logarithmic function (correlation coefficient R² = ). The results of this study are entirely consistent with previous field studies conducted in the world. Key words: Trawl net, vertical opening, trawling speed. I. INTRODUCTION Trawl net is one common and important fishing gear of the world. In Viet Nam, Trawls have been used for a long time and now Trawls are one of the most important types of fishing gear in Viet Nam. The fishing production from trawling is about 40% of total catch. Because of natural conditions in fishing grounds, trawl fishery only developed forcefully in the Northern and Southern provinces of Vietnam [2]. Trawl net were normally made of Polyethylene [2], it operates like a bag pulled by vessel, passing a volume of water including fish, the fish are filtered inside of net [4]. Shapes of the net play an important role on catching efficient of trawl net. One of those parameters is vertical openings, affecting on the ability to catch species which live near the bottom [5]. Bottom trawls are designed and rigged to have bottom contact during fishing. They are towed across the bottom at speed ranging from 1 to 7
