Evaluating the use of new technologies to reduce the large quantities of by-catch produced by bottom trawl fisheries


MINOUW partner & Lead scientist:

CSIC (Agencia Estatal Consejo Superior de Investigaciones Científicas), Montserrat Demestre

Fishing method and species:

Bottom trawl with 40-mm square mesh or 50-mm diamond mesh codends. The species targeted are Hake, red mullet, red shrimp, and Norway lobster.

What is the discards problem?

Mediterranean bottom trawls have low selectivity and therefore produce a large quantity of unwanted by-catch. Two types are produced: undersize fish of valuable commercial species (particularly Hake, Blue Whiting and Horse Mackerel), and non-commercial marine organisms.

What activities did the MINOUW project carry out?
  • Monitoring fish discarding practices.
  • Estimating handling and sorting costs.
  • Estimating the effectiveness of discards-reduction measures based on light technologies.
  • Assessing the effectiveness of pre-catch monitoring technologies using Deep Vision.
  • Assessing alternative mesh types to reduce unwanted catches.
What outcomes were expected?
  • Understand what factors lead to discarding practices and how new technologies (modifications to nets; use of lights) can mitigate the problem of discards in bottom trawl fisheries.
  • Foster fishers’ involvement in the process of finding solutions to mitigate the impact of the Landings Obligation in their activity.
  • Encourage fishing practices and technologies that minimize fishing impact on ecosystems.

The results are divided into two areas of research:


1.4a Testing if a modified trawl improves selectivity in Hake and Red mullet fisheries.

The results showed an important reduction in the undersized fraction of European hake (52%). In essence, the modification of the net is simple and practical to adopt, and contributes to the implementation of the landing obligation.

For a full summary of these results download the PDF here: (637kb)


1.4b The effect of using artificial lights on Norway lobster trawl fishery.

A decrease of biomass percentage of both commercial and discarded fraction has been detected when comparing control hauls with hauls with lights. Number of experimental hauls must be carried out to statistically test the results and determine if there is a real effective effect.

For a full summary of these results download the PDF here: (637kb)