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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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The effect of krill encountering meshes with different orientation.The penetration model (CS1_CS2) is rotated, at optimal attack angle perpendicular to the netting from 0–90°. 0° is a dorso ventral orientation equal to normal swimming orientation.
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pone-0102168-g010: The effect of krill encountering meshes with different orientation.The penetration model (CS1_CS2) is rotated, at optimal attack angle perpendicular to the netting from 0–90°. 0° is a dorso ventral orientation equal to normal swimming orientation.

Mentions: When examining the effect of cross section orientation and attack angle, we used only CS1_CS2, as CS3 was found to have no effect on the size selection of krill in the current trawl design. Figure 10 shows the potential effect of orientation of CS1_CS2 in the mesh for the relevant oa range rotated from a dorso-ventral orientation (see CS1 and CS2 in Fig. 2) (i.e., 0 to 90°). For the rotation range from 0 to 40°, the L50 value was nearly constant, indicating little effect of orientation over this range; it was only about 15–20% smaller than the maximal value obtained at 90° (Fig. 10). This relatively limited effect of rotation is also visible in Figure 5, but shows that individuals rotated 70–90° contrary to the other orientations will be retained by the mesh. Overall, the effect of cross section orientation in the mesh opening is relatively weak for a large range of rotation angles. This is due to the cross section shape of CS1_CS2, which is reasonably round shaped.


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

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

The effect of krill encountering meshes with different orientation.The penetration model (CS1_CS2) is rotated, at optimal attack angle perpendicular to the netting from 0–90°. 0° is a dorso ventral orientation equal to normal swimming orientation.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0102168-g010: The effect of krill encountering meshes with different orientation.The penetration model (CS1_CS2) is rotated, at optimal attack angle perpendicular to the netting from 0–90°. 0° is a dorso ventral orientation equal to normal swimming orientation.
Mentions: When examining the effect of cross section orientation and attack angle, we used only CS1_CS2, as CS3 was found to have no effect on the size selection of krill in the current trawl design. Figure 10 shows the potential effect of orientation of CS1_CS2 in the mesh for the relevant oa range rotated from a dorso-ventral orientation (see CS1 and CS2 in Fig. 2) (i.e., 0 to 90°). For the rotation range from 0 to 40°, the L50 value was nearly constant, indicating little effect of orientation over this range; it was only about 15–20% smaller than the maximal value obtained at 90° (Fig. 10). This relatively limited effect of rotation is also visible in Figure 5, but shows that individuals rotated 70–90° contrary to the other orientations will be retained by the mesh. Overall, the effect of cross section orientation in the mesh opening is relatively weak for a large range of rotation angles. This is due to the cross section shape of CS1_CS2, which is reasonably round shaped.

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