Are design or the size of the trawl affecting

the cod-end selectivity?

Marine Research Institute

Haraldur Arnar Einarsson MRI-Iceland

And

Ólafur Arnar Ingólfsson IMR-Norway

2 / 14Haraldur Arnar Einarsson

IntroBasics about the method

Codend design

• Nephrops trawl

Different method same codend

• One or two codend on the same trawl

Circumferences

• large commercial trawl

Different codends netmaterial on two different designed trawls

• Results within codeds on different trawls

• Results within trawls with different codends

Summary

Conclusion

3 3 / 14Haraldur Arnar Einarsson

Cover codend

50mm mesh in the cover with 40 mm meshes in the codend

Small kites lift the net from the codend in test

Basics about the method

Method

Test codend

Cover 50mm

4 4 / 14Haraldur Arnar EinarssonCodend design

Codend design

Two mesh sizes with two different circumferences each

90mm with 100 (normal ) and 134 (wide ) meshes around

105mm with 86 (normal ) and 114 (wide ) meshes around

5 / 14Haraldur Arnar EinarssonDifferent method

Same

One or two codend on the same trawl

Last year a trial with horizontal divided trawl in comparison with same trawl with one codend

The same codend was measured with cover codend method as single codend and as upper

codend at the divided trawl

Mesh size was 135mm (lower codend on the divided one was 155mm)

6 / 14Haraldur Arnar EinarssonDifferent method

One coded upper codend One coded upper codend

One coded upper codend One coded upper codend

SR

7 / 14Haraldur Arnar EinarssonCommercial

January 2013:

A selectivity measurements was done on board

in a commercial bottom trawler with common trawl

1. T90 in 120mm

2. Normal 135mm (100mesh)

3. Narrow 135mm (60 mesh )

Örfirisey RE 4

Bacalao

8 / 14Haraldur Arnar Einarsson

Narrow coded normal codend Narrow coded normal codend

Commercial

Same codend with 135mm meshes but different circumferences

9 / 14Haraldur Arnar Einarsson

Redesign on six day selectivity survey now in September (1-6 / 9)

Two trawls same codends

Two different trawls, both in size and design

On both trawls two different codends was measured with cover codend

36,6 Headline 70,2

22,6 Fishing-line 40

41 Length 81

45,5 Extension 90.5

Different cut on belly

14° ~8°

10 / 14Haraldur Arnar EinarssonTwo trawls same codends

Two codends tested

Green codend

Mesh 135mm

2x6mm PE

1040 g/100m

Yellow codend

Mesh 135mm

2x6,2mm PE

1585 g/100m

Same circumference

Same length

11 / 14Haraldur Arnar EinarssonTwo trawls same codends

12 / 14Haraldur Arnar EinarssonTwo trawls same codends

13 / 14Haraldur Arnar Einarsson

Summary

Summary

Mesh size is far from be the most important factor for codend selectivity

Circumference is a strong factor for codend selectivity

Wider codend reduces L50

Narrower codend increses L50

How the codend is used affects selectivity

- Two codend instead of one

- Grids in front of the codend....?

Codend material (twine) affects the selectivity

But it can vary greatly between the same codend attached

on different trawl

Trawl size and/or design has significant effect on codend selectivity

14 / 14Haraldur Arnar Einarsson

Conclusions

Conclusions

If laws or regulations are meant for promoting the wanted

selectivity from the gear. The whole design of the trawl and

codend must be taken into account.

Results from codend selectivity is only representative for the

codend in the trial and the trawl it is attached to.