Modifying selectivity to reduce unwanted catches in an English trammel net and gill net common sole fishery

Abstract Modifying the design and selectivity of commercial fishing gears can reduce unwanted catches. Most gear selectivity research focusses on trawl gears, and there are relatively few examples of modified static nets, such as gill and trammel nets, which are used all over the world. Fishers operating in the southeast England’s common sole (Solea solea) static net fishery wanted to explore methods to try to reduce the unwanted catches of thornback ray (Raja clavata). In 2017, the fishery had common sole landings of 343 tonnes making it an important local fishery. The largest port, the beach launch port of Hastings, is the home port for 65 vessels. Here we describe the performance of a modified trammel net with reduced mesh size in the two outer walls, intended to reduce catches of thornback rays without reducing the landings of the target species of common sole. There no published studies on modifying the outer meshes of a trammel net. The fieldwork was undertaken onboard a vessel from Hastings, fishing over ten days. The catches from a standard gill net, a standard trammel net and a modified trammel net were compared. Six fleets of nets were fished, each made up of five different net sections. The three net designs were placed into the fleets in a random set design. All of the net designs had a minimum (inner) mesh size of 90 mm. There was no statistically significant difference in the number of thornback ray caught between the nets but the number of common sole was estimated at 87 % higher by value in the modified trammel net compared to the other nets. Therefore, when using the modified trammel net, considerably less fishing effort was required to catch the same quota of common sole, but with no increase in the rate of thornback ray catches. If this design were to be applied more widely in this fishery, it could reduce overall catches of thornback ray. The study shows the difference in selectivity towards common sole, plaice (Pleuronectes platessa), whiting (Merlangius merlangus) and thornback rays between a gill net and two trammel net designs.