Gill Net Selectivity

[Leon Roskilly]

We've discussed gill net selectivity on previous threads, so I thought that some might have some thoughts about this information recently sent to me:

 

"The term used by fishermen and the literature of net suppliers is 'Twine size'.

 

There has been a reduction in twine size across many gill/tangle net types over time as the realisation that smaller (thinner) twine sizes are more efficient at trapping fish.

 

The down side is that during the process of clearing debris (mainly weed) which has to be removed from retrieved gill nets, thinner twines are more likely to be broken. Likewise in the removal of fish.

 

Twine diam. of 0.40 & 0.45 use to be the norm for bass/mullet gill nets but now 0.35 & 0.30 are frequently used.

 

Nets used on wrecks or rough ground are traditionally made in twines of 0.50 to 0.65. The twine technology now available also means that twines are softer and more flexible and have increased fish capturing properties.

 

Also, the setting ratios which were traditionally set by a third (this means that the sheet netting with a stretched length of 100 metre is set to head & foot line of 66 metres which allows the meshes to appear like vertical diamonds and results in a significant relationship between mesh size and size of fish retained) are increasingly being set by a half and I even heard of one guy who claimed to be setting a 100 metres of sheeting into just 33 metres of head/foot line.

 

This would have the effect of creating a sort of mass maze of folded meshes which would capture anything that touched it and the individual did say that the way he was setting his gear knocked any notion of established relationship between mesh size and retention of certain fish sizes (parabolic retention curves) into oblivion."

 

 

Tight Lines - leon

[stavey]

This has been my fear all along about mesh size leon, we know its all rubbish about more selective fishing by increasing mesh size not to catch this size and and only catch that size, we would not be this state with the fish stocks if it was'nt........

[ColinW]

If these nets are so selective, how come dolphins drown in them? I don't think I will live to see a bass as big as a dolphin!

[Tom Pinborough]

Kind of knocks the previous statements in other threads that big fish will bounce off and small fish swim through .

I also understand ( I phoned KESFC to check) there is no regulation on how the net lenght to head/foot rope lenght ratio is set , each fisherman tweeks his nets to suit.

 

 

cheers

Tom

[wurzel]

A gill net IS! selective, no matter how it is rigged the size of fish caught is governed by the mesh size.

most nets are rigged by 50% some usally small shallow sole or other flat fish like skate or turbot nets are rigged by 60 or 70%, if a fish is too small the majority will push through even spikey fish like bass and thornbacks, ok perhaps in a very slack net you might snag a few larger fish but if the fish is to big to get a mesh around it's head it stands a good chance of thrashing its way clear, some times a big bass or cod might get caught by it's lips or moustach as we call it, this is aways regarded as a bonus but for every one caught several get away.

As for useing very fine or very slack nets for a fish like bass, shure you might catch a few more fish but instead of one or two meshes around the gills you have loads, this makes it hard work to clear the fish, the fish is often damaged and looks terrible, the meshes are often broken that with the added dunage caught I've found it a waste of time.

On the other hand a 12" 065 rigged by 70% skate net is the most selective and clean fishing I've ever done.

[sam-cox]

I can honestly say that in the three summer bass netting I done only a hand full of undersized bass were caught. These fish would normally only be caught on the gill spikes and could be let go very alive.

I know some on hear think Im on the side of the commercials but Im only saying as I find.

Most fish caught in a 90mil bass nett will be of a uniform size of around a pound and three quarters, around 38cm.

The MLS is however way to small and should idealy be upped to 50cm a fish ound 3.5lb.

[Toerag]

For all those that reckon gillnets aren't selective go to www.cefas.co.uk/publications/lablea...ableaflet69.pdf and have a look at figure 10.

I'd say that's a pretty convincing statement of selectivity!