Appologies for the late reply as I've only just seen this thread. This is a good project but.... would it not be better to make the net out of square mesh rather than diamond, so that it cannot collapse, especially in the cod end. I have seen various nets already doing this to reduce the by-catch, so acceptance would be easier within the industry as several vessels are already trialling these designs and reporting back to their fellow trawlermen? Also using a square mesh design would put less stress on the rings as the net would not try to compress the square shape with the weight of the fish in the cod end as opposed to what happens with diamond shaped netting. I worry about the structural integrity of the rings, but more the fact that fishermen would not have time, desire, or the ability to check if they were working. To this end, would it not be better to weave luminescent material into the net, as the size of the ring is dictated by the size of the mesh and the ammount of technology it would need to incorporate (lights, batteries etc) so fitting any device is reducing the size of the escape area. You may be attracting a fish to an escape ring which it cannot fit through, rather than to a normal net aperture elsewhere that it can fit through. I have seen evidence that fish are attracted to light sources, but these are always under non stressful conditions ie. when they're hunting. Would a series of flashing rings surrounding a group of tired, trapped fish, not confuse/disorient them further? Especially as these fish are caught where they live, so even though it's a dark environment, they have senses including sight (lateral line etc), otherwise if they couldn't see/navigate effectively in darkness, they would be living somewhere else. It may be that very low level lights would work a lot better, again a luminescent material possibly woven into the mesh of the net and not requiring a power source. I also think that if you are using these rings then activation only when the boat is towing the net is important as if the net catches the bottom and has to be cut loose, you wouldn't want the lights to remain on or flashing, attracting fish to their death.
I think the best part of this design is lifting the net off the bottom to stop damage to the sea bed and to also reduce the net stirring up the bottom and re introducing plastic particles that have settled/been trapped, back into the food chain. However, from a fishing point of view, the chain/rock hoppers in a trawling net introduce noise, which attracts the fish, so you may want to consider introducing rattles on the front of the net, to maintain efficiency. This is important as any loss in the effectiveness of the net at collecting keepable fish will mean it will not be adopted by the industry.
I liked the way the net uses fish behaviours (if proven) to split out the species, however, fishermen still want to be able to catch cod, until they have met their quota, so the ability to drop this splitting element until they have their cod quota and to then release/install/hook the separating device in place would be an advantage.
Anyway, just a few suggestions
I do have serious doubts about the light rings working at all and if they do, then why not just make a whole portion of net light up as, towards the end of a trawl, when there are a lot of fish in the cod end, many of the lights would be obscured/blocked by larger fish anyway. I think you have the makings of a really good design, but have not pushed it as far as you will once competitions/masters deadlines are out of the way. I also accept I have not seen all the reaseach you have collated. I would be fascinated to see any of the light and fish behaviour stuff if you'd be wiling to send it or links to me: firstname.lastname@example.org