Limits...
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.

Show MeSH

Related in: MedlinePlus

Scanned pictures of krill with markings to illustrate the width and height at CS1 and CS2.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4126659&req=5

pone-0102168-g003: Scanned pictures of krill with markings to illustrate the width and height at CS1 and CS2.

Mentions: A two-step process was used to take morphological measurements. The first step involved taking measurements of 30 individuals covering the length span from 27 to 55 mm. Each individual was placed on a flatbed scanner to measure width and height at CS1 and CS2. Width and height were extracted using the image analysis in the FISHSELECT software (Fig. 3). After these measurements were taken, each individual was frozen on a metal plate at −80°C to ensure rapid freezing. The frozen individuals were cut with a scalpel at CS1 and CS2 perpendicular to the length of the body. The frozen condition prevented the specimens from deforming during the slicing, which would cause deviation from their natural morphology. These sliced cross sections were photographed on a flatbed scanner. Then based on the shape describtion by analyzing the cross section images, we found relations between the three parameters describing the cross section shapes and size and the height and width at the cross sections. This enabled us to assess the cross section shapes and sizes established for CS1 and CS2 for a larger number of individuals based on only measuring height and width at CS1 and CS2. In the second step, the length of 83 individuals with a length range from 19 to 54 mm was measured and the established length to cross-section relationship applied. Without cutting we assessed the cross sections CS1, CS2, and CS3 by placing a given specimen on the scanner for the different measures (height, width, and curled).


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

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

Scanned pictures of krill with markings to illustrate the width and height at CS1 and CS2.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0102168-g003: Scanned pictures of krill with markings to illustrate the width and height at CS1 and CS2.
Mentions: A two-step process was used to take morphological measurements. The first step involved taking measurements of 30 individuals covering the length span from 27 to 55 mm. Each individual was placed on a flatbed scanner to measure width and height at CS1 and CS2. Width and height were extracted using the image analysis in the FISHSELECT software (Fig. 3). After these measurements were taken, each individual was frozen on a metal plate at −80°C to ensure rapid freezing. The frozen individuals were cut with a scalpel at CS1 and CS2 perpendicular to the length of the body. The frozen condition prevented the specimens from deforming during the slicing, which would cause deviation from their natural morphology. These sliced cross sections were photographed on a flatbed scanner. Then based on the shape describtion by analyzing the cross section images, we found relations between the three parameters describing the cross section shapes and size and the height and width at the cross sections. This enabled us to assess the cross section shapes and sizes established for CS1 and CS2 for a larger number of individuals based on only measuring height and width at CS1 and CS2. In the second step, the length of 83 individuals with a length range from 19 to 54 mm was measured and the established length to cross-section relationship applied. Without cutting we assessed the cross sections CS1, CS2, and CS3 by placing a given specimen on the scanner for the different measures (height, width, and curled).

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