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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

Shapes of CS1, CS2 and CS3. CS1 is described by a flexellipse_1, CS2 is described by a flexellipse_3 and CS3 is described by a flexdrope_2 (see appendix S1).
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pone-0102168-g002: Shapes of CS1, CS2 and CS3. CS1 is described by a flexellipse_1, CS2 is described by a flexellipse_3 and CS3 is described by a flexdrope_2 (see appendix S1).

Mentions: We also considered the different ways in which krill can meet the meshes in a trawl (i.e., head first, tail first, curled, stretched), as this determines which additional measurements should be made during data collection. In this study we included a second contact mode, the curled shape, CS3 (Fig. 2). We expect that krill are more passive in a trawl compared with fish and thus might encounter the meshes in more random orientations. CS3 represents a contact mode very different from the optimal mode, and it is expected to result in low selectivity due to the large cross section shape. At this stage we chose to include only one contact mode in addition to the optimal contact mode. If the observed size selectivity of krill is difficult to explain by simulation the process using the optimal contact mode is a more detailed approach, involving more contact modes needed.


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

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

Shapes of CS1, CS2 and CS3. CS1 is described by a flexellipse_1, CS2 is described by a flexellipse_3 and CS3 is described by a flexdrope_2 (see appendix S1).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0102168-g002: Shapes of CS1, CS2 and CS3. CS1 is described by a flexellipse_1, CS2 is described by a flexellipse_3 and CS3 is described by a flexdrope_2 (see appendix S1).
Mentions: We also considered the different ways in which krill can meet the meshes in a trawl (i.e., head first, tail first, curled, stretched), as this determines which additional measurements should be made during data collection. In this study we included a second contact mode, the curled shape, CS3 (Fig. 2). We expect that krill are more passive in a trawl compared with fish and thus might encounter the meshes in more random orientations. CS3 represents a contact mode very different from the optimal mode, and it is expected to result in low selectivity due to the large cross section shape. At this stage we chose to include only one contact mode in addition to the optimal contact mode. If the observed size selectivity of krill is difficult to explain by simulation the process using the optimal contact mode is a more detailed approach, involving more contact modes needed.

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