Mitigating bycatch in trammel net fisheries using species-specific gear modifications

Small-scale fisheries (SSF) use static gears like hanging nets, which are thought to interact with marine ecosystems more benignly than towed gears. Despite this, trammel nets, one of the most regularly used fishing gears in the Mediterranean SSF, generate large amounts of discards, which can account for 25% or more of the captured biomass. Discarded organisms may include endangered or threatened species such as elasmobranchs, as well as non-commercial invertebrates that damage fishing gear or cause disentanglement delays. We tested various trammel-net gear modifications, including (a) the use of a guarding net attached to the footrope, (b) increasing the size of the rigging twine between the footrope and the netting panel, and (c) decreasing the mesh size of the outer panels. The last two modifications were successful in lowering captures of the marbled electric ray Torpedo marmorata, which is commonly discarded in the study area. Both sorts of modifications are relatively simple and inexpensive to implement. The current study shows that prior evaluation of the discards profile of distinct métiers is essential to accomplish species-specific gear modifications and underlines the importance of collaboration among scientists, fishers and gear manufacturers.