The Sep-Nep is an inclined panel of diamond netting to sieve the nephrops into the lower chamber and direct the fish into the upper chamber. The nephrops can be further selected within the lower chamber by fitting a rigid grid to release the small ones and direct the marketable nephrops into the lower cod-end.
The Seltra box is a selective device that originates from Denmark and Sweden where the standard two panel trawl is transformed into a four panel ‘box’ section in the extension of the net. It is transformed to a four-panel because this configuration is found that the net maintains a more open cross section. This helps to smooth out the water flow into the cod-end and allows the captured fish swim leisurely for a longer before falling back into the cod-end. Giving them a greater time to find an escape route.
For many fish such as haddock and whiting the escape route will be upwards, for this reason the top panel of the Seltra is made from either larger diamond mesh 270mm in some fisheries or large square mesh, anything from 140mm to 300mm square mesh is commonly used. This device can be used with the standard two-panel cod-end or the four panels can be continued to form a four-panel cod-end. The four-panel is probably better as it helps to maintain the open shape of the extension right down into the cod-end. This allows the fish space with in the cod-end to keep swimming in the relatively slow water flow in this area and helps to prevent the catch from getting packed into the cod-end where they are susceptible to damage through contact with other fish and shellfish in the cod-end.
The Sep-Nep is the result of combining several similar projects that were being worked on in the Dutch nephrops fishery. A panel of diamond mesh is inserted on an incline in the back end of a standard nephrops trawl to sieve the catch. The fish being directed into an upper cod-end and the nephrops falling through the panel and into the lower chamber. This allows separate secondary selection that is suitable for the different species to be made in each cod-end.
In this gear they opted for simple a larger diamond mesh in the upper cod-end for to improve the size selection of the fish. In the lower cod-end a small rigid grid was fitted for sharper size selection of the nephrops with the small ones being released. A curtain of weighted roped was suspended just ahead of this grid to ensure all the nephrops were directed towards the bottom of the net to maximise their contact with the rigid grid.
These multiple selection devices should improve selection and help to minimise discarding of both fish and nephrops. As with any other gear where nephrops are separated from fish, the quality of both is maintained while in the trawl and should result in an improved product being taken onboard the vessel.
All dimensions, mesh counts and cutting rates are for generic advice and information. Before constructing and fitting this gear into a trawl you should consult with your local fishery officers or legislators such as MMO, Marine Scotland and Daera in the UK. This should ensure that your gear meets the requirements of the area that your vessel will be fishing in.