Use a larger codend mesh size on trawl nets
Overall effectiveness category Likely to be beneficial
Number of studies: 1
Background information and definitions
Trawling is a method of fishing that involves pulling a fishing net (trawl) through the water behind one or more boats. Trawl nets can catch a considerable number of unwanted organisms, including non-commercially targeted species and organisms under the legal-size limit. Nets are traditionally made of diamond-shaped mesh throughout, including at the codend. To reduce the amount of unwanted organisms caught, a codend made of larger size mesh can be used, with the aim to allow smaller unwanted organisms to escape, while retaining the commercially targeted ones (Burgos‐León et al. 2009).
Evidence related to other codend modifications are summarised under “Threat: Biological resource use – Use a square mesh instead of a diamond mesh codend on trawl nets”.
Burgos‐León A., Pérez‐Castañeda R. & Defeo O. (2009) Discards from the artisanal shrimp fishery in a tropical coastal lagoon of Mexico: spatio‐temporal patterns and fishing gear effects. Fisheries Management and Ecology, 16, 130–138.
Supporting evidence from individual studies
A replicated, paired, controlled study (year unspecified) of three estuarine sites in the Celestun Lagoon, Gulf of Mexico, Mexico (Burgos-León et al. 2009) found that trawl nets fitted with a 2.5 cm mesh codend instead of a traditional 1.3 cm mesh caught fewer combined non-commercial unwanted invertebrate and fish species (discard) and lower biomass and abundance of discarded organisms. On average, nets with the larger mesh codend caught fewer discard species (3–12) than nets with the traditional codend (12–20). Biomass and abundance of discards were on average lower with the larger mesh codend (biomass: 2–10 g/245 m2; abundance: 0.7 individuals/245 m2) than with the traditional codend (biomass: 22–57; abundance: 37). Nets with the larger mesh codend also caught less biomass and abundance of commercially targeted shrimps (biomass: 3–15 g/245 m2; abundance: 1 individual/245 m2) than nets with the traditional codend (biomass: 15–39; abundance: 20). This however led to similar biomass ratios of commercially targeted to discard species for both mesh sizes (1:1). On three occasions at each of three sites, a vessel towed two identical bottom-nets simultaneously over 100 m during paired deployments, one fitted with the traditional codend, the other with the larger mesh codend. For each deployment, discarded organisms were identified and their combined weight and counts recorded. Weights of commercially targeted shrimps were also recorded.Study and other actions tested