Trammel Netting (image © Seafish).
Trammel nets are multi-layered monofilament (nylon) nets that are set on the seabed. An inner mesh of 10.5 inches entangles fish, which then push through a mesh of one of the two outer layers (usually 36” mesh) which help the net to more effectively envelope the fish and results in better retention of the catch. Local fisheries bylaws govern mesh sizes within the Cornwall inshore fisheries district, and outside the 12 mile limit EU regulations govern the allowable mesh sizes. By regulating mesh size undersized or non-target species are more likely to escape capture.
There are occasional issues with entanglement of non-target species such as pink sea fans, sharks and rays, and occasionally seals and cetaceans such as dolphins and porpoises. Research has shown that cetacean bycatch can be reduced by the use of acoustic deterrents such as sonic ‘pingers’ that deter cetaceans from the area close to the net. All of Cornwall’s netting vessels over 12m in length are now using pingers.
If nets become snagged on the seabed or get towed away by other fishermen they are lost. Lost nets can continue to fish and are often termed ‘ghost nets’. They pose a real threat to marine life. The length of time they continue to fish depends on many factors, though fishermen argue that strong currents will roll the nets until they are no longer a threat. More evidence is needed to support this.