Selectivity trials in the Irish Sea - Seafish

Irish Sea Nephrops 

Selectivity Project 

Mike Montgomerie 

Gear Technologist 

Seafish 

supporting the seafood industry for a sustainable, profitable future

SEAFISH SELECTIVITY 

PROBLEM? 

Need to evidence less than 1.5% of cod in the catches 

Only device approved by EU is the Swedish grid. 



Northern Ireland – Nephrops Selectivity Project 

Initiated by AFBI and ANIFPO 

Funded by EFF and DARD. 

Seafish – Project Managers 

Co-ordinated by steering group comprising of Seafish, 

DARD, AFBI, ANIFPO, NIFPO and local netmakers 



Nephrops Selectivity Project 

Objectives 

To investigate the reduction of discards in trawls used 

in the Irish Sea Nephrops fishery by trialling three 

different gear designs. 

Increased to four to include the Swedish Grid. 



Northern Ireland – Nephrops Selectivity Project 

Gear Designs 

Low headline, coverless trawl 

Box codend and extension 

Plastic Grids 

Increased to four to include the Swedish Grid. 


Swedish Grid 

The grid used was made from aluminium, 

28mm on the circumference with 15mm vertical bars. 

35mm spacing in accordance with regulation. 

1.2m by 0.750mm hinged in the middle. 

To be fitted in between the tapered section and the codend 


Swedish Grid 


Swedish Grid 


Swedish Grid 

It works in that it separates fish from nephrops! 

Catch from the control net 

Catch from the net fitted with 

a Swedish grid 


Swedish Grid 

13 hauls on twin rig vessel – 4 were had very little in experimental 

codend due to obstructions in the grid. 

8 hauls with single rig boats – 

the grid obstructed with debris every haul! 

In the good hauls the grid did release almost all fish larger than 20 

cms 

In the twin rig it reduced the cod from 0.71% of the total catch to 0.18% 

in single rig 

Very little loss of nephrops unless the grid obstructed 


Swedish Grid 

Handling was a problem. 

The grid comes aboard in a rigid form. This is extremely cumbersome 

and dangerous to take on board. 


Swedish Grid 

Handling was a problem. 

The grid comes aboard in a rigid form. This is extremely cumbersome 

and dangerous to take on board. 

Lost several hauls through the grid blocking up. 

If the grid was blocked at all there was very little in the codend 


Swedish Grid 


Swedish Grid 

Evidence of meshing of nephrops through the mis-shapen meshes in 

the vicinity of the grid 

In perfect circumstances the grid will exclude all of the larger round fish 

These problems are reiterated by other vessels from Southern 

Ireland who are using the grid regularly in that in many areas they 

cannot work the grids due to blocking with debris, shellfish and mud 

balls. 


Swedish Grid 

Evidence of abrasion on the lower side of the grid suggesting that 

the grid was rubbing and possible ‘ploughing’ into the seabed. 

Swedish grid clogged with mud inside the net where the grid 

has been digging into the seabed.. 


Plastic Flexible Grids 

Two versions of the plastic grid 

Both grids had 45mm bar spacing 

A the bottom to allow bottom fish through. 

Both are 1.5m X 0.8m 

Fitted approximately 5m from the end of the taper. 



Plastic semi rigid grids 



Position of plastic grid 

in the trawl. 





With plastic grid 

With out plastic grid 



Stornoway Grid 

Very easy to handle - No serious safety problems with handling 

Hauled onto the netdrum with no problem 

Shot away and returned to shape very well 





Twin Rig –Stornoway Grid 

Did reduce the bycatch of round fish to some extent. 

Lost quite a few nephrops – this could be due to wider bars (25mm) on this 

grid. 

Blocked up easily – lost 4 out of 14 hauls due to blockages – 

If blocked at all very little in the codend. 

It seemed more prone to blocking with large fronds of seaweed than the 

aluminium grid. 





12 hauls on twin rig vessel –5 were had very little in experimental 

codend due to obstructions in the grid. 

Increased the percentage of cod from 0.01 in control net to 0.04 in the 

experimental net! 

Total catch in experimental net was reduced to 55% of that in the control 

net. 

Reduction in nephrops by 50% overall 



Single rig – Carlsen Grid 

Due to poor results on twin rig trials with Stornoway grid the Danish 

one was used on the Single rig vessels. 

Grid fitted in same position as other plastic grid. 

More awkward to handle and still prone to choking up. 

Needs all the crew there to haul the trawl even in good weather. 




Carlesen Grid 




12 hauls on twin rig vessel – again 5 were had very little in 

exerimental codend due to obstructions in the grid. 

A Reduction in the percentage of cod from 6.7% in the control net to 

0.4% in the net with the grid fitted. 

Reduction in total catch and nephrops 




Trying to take the plastic grid 

through a powerblock one of the 

single rig vessels.. 

Plastic grid clogged with 

seaweed and debris on one of 

the single rig vessels.. 


Low headline Coverless trawl. 

Trialled on the understanding that cod tend to swim higher of the 

seabed in Irish Sea than in other areas. 

Two versions of coverless / low headline trawls were made. 

One suitable for the single rig vessels by Norman Kelly. 

One for the twin rig vessel by Jim Hamilton. 

Both netmakers used their standard prawn trawl as a basis. 

Extended the headline to be the same length as the footrope and 

reduced the number of meshes in the wings to reduce the headline 

height. 



Standard trawl 

Coverless trawl 



Very easy to handle 

Easier to tow than the normal trawl 

Very little difference in catches of cod. 

Very little difference in nephrops catches 

Not much difference in discards – this is probably due to the standard 

prawn trawl already having a low headline height. 

Evidence of nephrops being lost through 160mm mesh in top panel, 

particularly close to selvedges. 

Not enough larger round fish on the grounds for a coverless trawl to 

work to its maximum on either vessel. 


Boxed Codend Extension 

Or Seltra Trawl 

4 panels for the extension instead of the normal 2. 

80mm Diamond 

mesh side and 

bottom panels 

200mm square mesh top 

panel 

Standard two panel 

extension and codend 

4 panel (boxed) extension 

section 

Main body of the 

trawl 



Easy to use 

No appreciable difference in nephrops catches 

Noticeable reduction in cod catches 

Noticeable difference in discards 

No obvious problems with device 



Refined version of the Boxed codend - Twin rig 

300mm square mesh in the top panel. 

Stretching from existing 90mm square mesh panel aft for 6.75m 

Using vessels standard codend to ensure continuity of results. 




Large square mesh 

increased from 

200mm to 300mm 

mesh. Length of panel 

increase from 4m to 

6.5approx. 

Continue to use standard 2 

panel codend 

Main part of 

the trawl 

codend 

Continue large square mesh further up the body of the 

trawl (tapered section) approx 1.5m. 







12 hauls on twin rig vessel – no real benefit from increasing panel 

size or mesh size 

A Reduction in the percentage of cod from 0.46% in the control net to 0.1% 

18% reduction in total catch. 

Reduction in nephrops approximately 4% 



Refined version of the Boxed codend - single rig 

300mm square mesh in the top panel. 

4m long – 50mesh section in 70mm netting 

Using vessels standard codend to ensure continuity of results. 




70mm 

Diamond 

mesh side and 

bottom panels 

Main body of 

the trawl 

300mm square 

mesh top panel 

4 panel (boxed) 

extension section. 

4 metres long 

Standard two 

panel extension 

and codend 




Similar results to the original boxed section extension 


Problems achieving the 1.5% cod if the selective device is 

efficient at reducing the overall discards. 

No incentive in regulation to reduce all discards – just to 

reduce cod. 

Problems with measurement of weight of total catch on 

most fishing vessels. 


Irish Sea Nephrops 

Selectivity Project 

Mike Montgomerie 

Gear Technologist 

Seafish

Selectivity trials in the Irish Sea - Seafish

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