Abstract
The Antarctic krill (Euphausia superba) is one of the most abundant resources in the ocean, which provides food for several important species in the Antarctic Ocean, and is targeted commercially by humans for many decades. To sustainably manage and harvest the species, energy-efficient, catch-efficient, and selective fishing gears should be developed for the Antarctic krill trawl fishery. This study investigates the effect of twine area and the liner length on the engineering performance of trawl through flume tank testing of trawl model to predict the performance of the full-scale midwater trawl used in the Antarctic krill fishery. Four 1/35th scale trawl model nets with varying lengths of the liner, based on the traditional trawl used in the Antarctic krill fishery, were designed using modified Tauti’s law and were tested in a flume tank at different towing speed, door spread, heavy bob weight, and the ratio of buoyancy to the fishing line (F/G). The results showed that the reduction in liner length by 25 and 50% from the traditional trawl net led to the decrease in twine area by 11.01 and 19.31% and, consequently, resulted in reductions in the lower bridle tension by 12.44 and 19.78%, and increases in energy efficiency by 17.98 and 25.73%, respectively. In addition, the reduction in liner length by 25 and 50% were found to increase the net mouth opening by 2.63 and 5.38% and the swept area by 6.52 and 8.38%, respectively, both of which are proportional to catch rates. Although the trawl net with 50% liner length is more energy-efficient and large mouth opening than those of the trawl net with the liner length over 75% of the trawl body, the large mesh section without a liner can result in the escape of the krill from the trawl, reducing overall catch efficiency. We, therefore, recommend the trawl with 75% of liner length as a suitable design for Antarctic krill considering energy efficiency and catch efficiency.
Highlights
The Antarctic krill (Euphausia superba) is a fundamental component of the complex ecosystem of the Antarctic Ocean (Punchihewa and Krishnarajah, 2013; Bairstow et al, 2021)
The trawls without, with 50, and 75% liner were designed to contain a small amount of twine in the main body compared with the trawl net with 100% liner and those used in the Antarctic krill fisheries
The modifications to the krill trawl net in this study reduced the twine area and drag force by 8.6 to 24.49% than that obtained by Xu et al (2015) and Feng et al (2017), who modified the total length of trawl and the net mouth circumference to improve the engineering performance of Antarctic krill trawls
Summary
The Antarctic krill (Euphausia superba) is a fundamental component of the complex ecosystem of the Antarctic Ocean (Punchihewa and Krishnarajah, 2013; Bairstow et al, 2021). The small mesh liners are widely used in krill trawls and cover various proportions of the trawl body length from 0% (without liner) to 100% (covering the entire trawl body) (Xu et al, 2015; Li et al, 2017) These liners are designed as a series of overlapping cones, resulting in a wave motion that gently ripples with the water flow and prevents small organisms from meshing (Engås et al, 2013; Underwood et al, 2016; Zhou et al, 2016). The introduction of the small mesh size liner trawl resulted in great increases in the catch, it was observed to move in a wave motion toward the codend, resulting in higher hydrodynamic drag of the trawl system, reduced spread and mouth opening, and lower size selectivity (Engås et al, 2013, 2014; Xu et al, 2015)
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