Abstract
Trawlers involved in the Antarctic krill (Euphausia superba) fishery use different trawl designs, and very little is known about the size selectivity of the various gears. Size selectivity quantifies a given trawl's ability to catch different sizes of a harvested entity, and this information is crucial for the management of a sustainable fishery. We established a morphological description of krill and used it in a mathematical model (FISHSELECT) to predict the selective potential of diamond meshes measuring 5–40 mm with mesh opening angles (oa) ranging from 10 to 90°. We expected the majority of krill to encounter the trawl netting in random orientations due to high towing speeds and the assumed swimming capabilities of krill. However, our results indicated that size selectivity of krill is a well-defined process in which individuals encounter meshes at an optimal orientation for escapement. The simulation-based results were supported by data from experimental trawl hauls and underwater video images of the mesh geometry during fishing. Herein we present predictions for the size selectivity of a range of netting configurations relevant to the krill fishery. The methods developed and results described are important tools for selecting optimal trawl designs for krill fishing.
Highlights
The largest annual catch of Antarctic krill (Euphausia superba, hereafter called krill) in the Southern Ocean since the inception of a commercial fishery in 1972 was 528,000 tons
Using the combination of this morphological description, realistic oa values for the meshes based on underwater observations made during commercial fishing operations, and experimental selectivity data, we were able to predict the selectivity for krill for different mesh sizes
Predicting the size selectivity of existing netting configurations and optimizing the size selectivity of future trawls designs based on management specifications in relation to the size selection
Summary
The largest annual catch of Antarctic krill (Euphausia superba, hereafter called krill) in the Southern Ocean since the inception of a commercial fishery in 1972 was 528,000 tons. The objectives of responsible harvesting of krill, rational management of the krill fishery, and economic profit for the industry demand development of fishing gear that reduces accidental (escape) mortality during the fishing process. Both the Commission and Scientific Committee of the CCAMLR strongly recommend member states that are fishing for krill to investigate the effects of different fishing gears on krill escapement to assess the total mortality of the krill stock caused by the fishery [7,8]
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