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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

Illustration of how the effective mesh openings in a trawl can vary depending of the attack angle of krill (5–90°) (A).The light mesh is the real mesh in 90° view and the dark mesh is the effective mesh opening when projecting the mesh opening to a plan perpendicular to the towing direction. The lower mesh series (B) shows the potential effect of rotation of the cross section (CS1_CS2) in a 30° open mesh.
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pone-0102168-g005: Illustration of how the effective mesh openings in a trawl can vary depending of the attack angle of krill (5–90°) (A).The light mesh is the real mesh in 90° view and the dark mesh is the effective mesh opening when projecting the mesh opening to a plan perpendicular to the towing direction. The lower mesh series (B) shows the potential effect of rotation of the cross section (CS1_CS2) in a 30° open mesh.

Mentions: We explored the potential effect of orientation of CS1_CS2 in the mesh opening and the effect of attack angles between krill and the netting for the specific gear for which we collected experimental size selection data. In principle, orientation of the cross section and the attack angle work in combination, but for simplicity we assessed their potential effects separately. We therefore examined the effect of orientation of CS1_CS2 using an optimal attack angle; in this scenario, the description of CS1_CS2 was presented perpendicular to the mesh (90° in Fig. 5 Panel A) and then was rotated stepwise from 0 to 90° (Fig. 5 Panel B). To evaluate the effect of the attack angle was the mesh shape stepwise projected to a plan perpendicular to the towing direction in steps of 10° (Fig. 5). The description of CS1_CS2 during this procedure was orientated optimally in the projected mesh shape. This analysis was conducted using the FISHSELECT software.


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

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

Illustration of how the effective mesh openings in a trawl can vary depending of the attack angle of krill (5–90°) (A).The light mesh is the real mesh in 90° view and the dark mesh is the effective mesh opening when projecting the mesh opening to a plan perpendicular to the towing direction. The lower mesh series (B) shows the potential effect of rotation of the cross section (CS1_CS2) in a 30° open mesh.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0102168-g005: Illustration of how the effective mesh openings in a trawl can vary depending of the attack angle of krill (5–90°) (A).The light mesh is the real mesh in 90° view and the dark mesh is the effective mesh opening when projecting the mesh opening to a plan perpendicular to the towing direction. The lower mesh series (B) shows the potential effect of rotation of the cross section (CS1_CS2) in a 30° open mesh.
Mentions: We explored the potential effect of orientation of CS1_CS2 in the mesh opening and the effect of attack angles between krill and the netting for the specific gear for which we collected experimental size selection data. In principle, orientation of the cross section and the attack angle work in combination, but for simplicity we assessed their potential effects separately. We therefore examined the effect of orientation of CS1_CS2 using an optimal attack angle; in this scenario, the description of CS1_CS2 was presented perpendicular to the mesh (90° in Fig. 5 Panel A) and then was rotated stepwise from 0 to 90° (Fig. 5 Panel B). To evaluate the effect of the attack angle was the mesh shape stepwise projected to a plan perpendicular to the towing direction in steps of 10° (Fig. 5). The description of CS1_CS2 during this procedure was orientated optimally in the projected mesh shape. This analysis was conducted using the FISHSELECT software.

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