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Size selection of Antarctic krill (Euphausia superba) in trawls.

Krag LA, Herrmann B, Iversen SA, Engås A, Nordrum S, Krafft BA - PLoS ONE (2014)

Bottom Line: 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.The methods developed and results described are important tools for selecting optimal trawl designs for krill fishing.

View Article: PubMed Central - PubMed

Affiliation: DTU Aqua, Technical University of Denmark, Hirtshals, Denmark.

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.

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Krill sliced at cross section 1 (CS1) and cross section 2 (CS2).
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pone-0102168-g001: Krill sliced at cross section 1 (CS1) and cross section 2 (CS2).

Mentions: Before initiation of the laboratory trials, the krill body was examined to identify the relevant morphology that potentially would determine the animal's ability to penetrate different meshes. We first determined the body orientation that would allow the largest individual to escape through a given mesh, as this orientation is indicative of the selective potential for krill for that mesh type. The optimal orientation for krill is when the body is stretched and meets the mesh opening head or tail first. We next identified morphological measures that could describe this optimal orientation. Two cross sections, CS1 and CS2, were identified along the length axis of the krill body as being decisive for size selection, as these cross sections contain the maximum height (h) and width (b) measures of animals in the optimal orientation (Fig. 1).


Size selection of Antarctic krill (Euphausia superba) in trawls.

Krag LA, Herrmann B, Iversen SA, Engås A, Nordrum S, Krafft BA - PLoS ONE (2014)

Krill sliced at cross section 1 (CS1) and cross section 2 (CS2).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126659&req=5

pone-0102168-g001: Krill sliced at cross section 1 (CS1) and cross section 2 (CS2).
Mentions: Before initiation of the laboratory trials, the krill body was examined to identify the relevant morphology that potentially would determine the animal's ability to penetrate different meshes. We first determined the body orientation that would allow the largest individual to escape through a given mesh, as this orientation is indicative of the selective potential for krill for that mesh type. The optimal orientation for krill is when the body is stretched and meets the mesh opening head or tail first. We next identified morphological measures that could describe this optimal orientation. Two cross sections, CS1 and CS2, were identified along the length axis of the krill body as being decisive for size selection, as these cross sections contain the maximum height (h) and width (b) measures of animals in the optimal orientation (Fig. 1).

Bottom Line: 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.The methods developed and results described are important tools for selecting optimal trawl designs for krill fishing.

View Article: PubMed Central - PubMed

Affiliation: DTU Aqua, Technical University of Denmark, Hirtshals, Denmark.

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.

Show MeSH
Related in: MedlinePlus