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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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Related in: MedlinePlus

Diamond mesh design guide for Krill, based in combination of CS1 and CS2.The plot gives iso-L50 curves as a function of mesh size (mm) and mesh opening angle (oa).
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pone-0102168-g006: Diamond mesh design guide for Krill, based in combination of CS1 and CS2.The plot gives iso-L50 curves as a function of mesh size (mm) and mesh opening angle (oa).

Mentions: The design guide based on CS1_CS2 was used to predict the basic selective properties for krill for all relevant sizes of diamond mesh when the individuals meet the meshes at the optimal orientation (Fig. 6). The design guide covers the mesh size range from 5 to 40 mm and the opening angle range from 10 to 90°. The size selectivity of krill depends greatly on the mesh opening angles. This is especially true for meshes with oa values ranging from 10–45° where meshes with larger oa values have less effect on the predicted L50. The predicted L50 for a given mesh size is however increasing towards a mesh opening angle of 90° (which equals a square mesh). The design guide further indicates that even the small meshes used in some survey trawls (∼7 mm) can be selective if the meshes are sufficiently open; if true, such surveys may underestimate the density of juvenile krill.


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

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

Diamond mesh design guide for Krill, based in combination of CS1 and CS2.The plot gives iso-L50 curves as a function of mesh size (mm) and mesh opening angle (oa).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0102168-g006: Diamond mesh design guide for Krill, based in combination of CS1 and CS2.The plot gives iso-L50 curves as a function of mesh size (mm) and mesh opening angle (oa).
Mentions: The design guide based on CS1_CS2 was used to predict the basic selective properties for krill for all relevant sizes of diamond mesh when the individuals meet the meshes at the optimal orientation (Fig. 6). The design guide covers the mesh size range from 5 to 40 mm and the opening angle range from 10 to 90°. The size selectivity of krill depends greatly on the mesh opening angles. This is especially true for meshes with oa values ranging from 10–45° where meshes with larger oa values have less effect on the predicted L50. The predicted L50 for a given mesh size is however increasing towards a mesh opening angle of 90° (which equals a square mesh). The design guide further indicates that even the small meshes used in some survey trawls (∼7 mm) can be selective if the meshes are sufficiently open; if true, such surveys may underestimate the density of juvenile krill.

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