Prohibit high grading in which only the most profitable individuals or species are landed

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • One study examined the effects of prohibiting high grading in which only the most profitable individuals or species are landed on marine fish populations. The study was in the North Sea/North Atlantic Ocean (UK).






  • Commercial catch abundance/landings (1 study): One replicated, before-and-after study in the North Sea/North Atlantic Ocean reported that a ban on high grading did not eliminate the discarding of legal-sized but unwanted common megrim Lepidorhombus whiffiagonis that were required to be landed.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, before-and-after study in 2008–2012 of a fished area of seabed in the North Sea/North Atlantic Ocean, UK (Macdonald et al. 2014) reported that a ban on high grading did not prevent the discarding of legal-sized but unwanted common megrim Lepidorhombus whiffiagonis that were required to be landed. Data were not tested statistically. Across all catches, the proportion of megrim above minimum landing size discarded and classed as “bruised” remained widespread both after (2010–2012) and before (2008–2009) high grading was prohibited (after: 0.10–0.15, before: 0.13–0.15). Similarly, legal-sized but “small” megrim continued to be discarded, but in increasingly lower proportions (after: 0.1–0.36, before: 0.32–0.39). High grading was prohibited in the North Sea in 2009 and meant that any species managed under quotas (such as megrim) was required to be landed if above minimum landing size. Data were collected by on board sampling of catches on eight demersal (bottom) fishing vessels based in the Shetland Islands, Scotland, and working in the mixed demersal fishery in the northern North Sea/North Atlantic Ocean (International Council for the Exploration of the Sea (ICES) Division IVa). Observer trips (2–8 d) were undertaken between May 2008 and March 2012. A total of 25 trips (22 twin trawl and 3 seine) and 407 hauls were sampled. Megrim length was recorded from the retained and discarded portions of the catch. Discards were categorized as “small” or “bruised”.

    Study and other actions tested
Please cite as:

Taylor, N., Clarke, L.J., Alliji, K., Barrett, C., McIntyre, R., Smith, R.K., and Sutherland, W.J. (2021) Marine Fish Conservation: Global Evidence for the Effects of Selected Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Marine Fish Conservation

This Action forms part of the Action Synopsis:

Marine Fish Conservation
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