Use a larger mesh size on trammel nets
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Some fisheries use static nets, such as trammel nets, that are left in the water to passively catch the commercially targeted species. Trammel nets are a wall of netting, usually comprised of three layers: a slack central layer with a small mesh sandwiched between two outer layers with a much larger mesh. The net is kept vertical by floats on the headrope and weights on the bottom rope. Trammels are considered to have less environmental impact than trawl nets, as they have minimal contact with the seabed and are more species and size-selective, however they have been shown to also result in some unwanted catch of invertebrates (Erzini et al. 2006; Gonçalves et al. 2007). To reduce the amount of unwanted catch in trammel net fishing, the mesh size can be increased, to potentially allow more organisms to escape (Gonçalves et al. 2008).
Erzini K., Gonçalves J.M., Bentes L., Moutopoulos D.K., Casal J.A.H., Soriguer M.C., Puente E., Errazkin L.A. & Stergiou K.I. (2006) Size selectivity of trammel nets in southern European small-scale fisheries. Fisheries Research, 79, 183–201.
Gonçalves J.M.S., Bentes L., Coelho R., Monteiro P., Ribeiro J., Correia C., Lino P.G. & Erzini K. (2008) Non‐commercial invertebrate discards in an experimental trammel net fishery. Fisheries Management and Ecology, 15, 199–1210.
Gonçalves J.M.S., Stergiou K.I., Hernando J.A., Puente E., Moutopoulos D.K., Arregi L., Soriguer M.C., Vilas C., Coelho R. & Erzini K. (2007) Discards from experimental trammel nets in southern European small-scale fisheries. Fisheries Research, 88, 5–14.
Supporting evidence from individual studies
A replicated, controlled study in 2001 off the coast of Algarve, southern Portugal, North Atlantic Ocean (Gonçalves et al. 2008) found that using larger mesh sizes in the inner and/or outer panels of trammel nets did not affect the community composition or reduce the abundance of unwanted catch of non-commercial invertebrates (discard). Discard community composition was similar in all six mesh-size configurations tested (data presented as statistical model results and graphical analyses). This was also true for their abundance which ranged from 21 to 29 individuals/1,000 m of net (corresponding to 39–54% of the total catch). Between January and December 2000, six trammel net configurations were tested during 40 fishing trials. Each configuration consisted of a combination of one of two sizes of large-mesh outer panels (600 or 800 mm) and one of three small-mesh inner panels (100, 120, or 140 mm). A total of 150 nets were deployed in groups (30 nets/group). For each group, five nets of each configuration were joined by a footrope (2-m gap between each net). For each configuration, catches were sorted into commercial (fishery target species and commercial bycatch) and unwanted non-commercial species (invertebrate discards), identified and counted. Commercial catch data for each configuration were not reported.Study and other actions tested