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Providing evidence to improve practice

Action: Use a larger codend mesh size on trawl nets Subtidal Benthic Invertebrate Conservation

Key messages

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  • One study examined the effects of using a larger codend mesh size on trawl nets on unwanted catch of subtidal benthic invertebrate populations. The study was in the Gulf of Mexico (Mexico).

 

COMMUNITY RESPONSE (1 STUDY)

  • Unwanted catch species richness/diversity (1 study): One replicated, paired, controlled study in the Gulf of Mexico found that trawl nets fitted with a larger mesh codend caught fewer combined species of non-commercial unwanted invertebrates and fish compared to a traditional codend.

POPULATION RESPONSE (1 STUDY)

  • Unwanted catch abundance (1 study): One replicated, paired, controlled study in the Gulf of Mexico found that trawl nets fitted with a larger mesh codend caught lower combined biomass and abundance of non-commercial unwanted invertebrates and fish compared to a traditional codend.

OTHER (1 STUDY)

  • Commercial catch abundance (1 study): One replicated, paired, controlled study in the Gulf of Mexico found that trawl nets fitted with a larger mesh codend caught less biomass and abundance of commercially targeted shrimps compared to a traditional codend, but that the biomass ratios of commercially targeted to discard species was similar for both.

Supporting evidence from individual studies

1 

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.

Referenced papers

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K., and Sutherland, W.J. (2019) Subtidal Benthic Invertebrate Conservation: Global Evidence for the Effects of Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.