Are differences in the choice of measures when reporting results slowing down the development of horizontally divided trawl gears?

Activity: Talks and presentationsConference presentations


The implementation of the landing obligation in European waters puts new focus on the development of selective fishing gears. Horizontally divided codends with different selective properties for fish and Nephrops can be used to both reduce bycatch and improve catch quality. The first step in the gear development is optimal separation of species into different compartments. The high variation in both inter- and intra-specific separation reported in the literature makes identifying and interpreting response patterns across studies difficult, if not
impossible if the measure of separation is confounded with one or more of the affecting factors. The aim of this study was to review the literature to compare the separation of species when using three measures; overall proportion, preference and preference by length class. Overall proportion is the amount of individuals entering a compartment of the total number of individuals in the catch. Preference is taking into account the proportion of the compartments
relative to the total height of the gear at the point of separation, and indicate when a species deviate from a uniform distribution. Preference by length class makes it possible to identify differences in vertical distribution. Examples of the performance of the gear design, and interpretation of the vertical behavior of across studies is given for the three types of measures. Also, it is shown that the species specific preference for a compartment changes from the gear mouth to the codend.
Period27 Sept 2018
Event titleICES Annual Science Conference 2018
Event typeConference
LocationHamburg, GermanyShow on map
Degree of RecognitionInternational


  • horisontally divided codend
  • catch separation
  • catch proportion
  • species-specific preference
  • vertical distribution