Study

Evaluation of three levels of selective devices relevant to management of the Danish Kattegat–Skagerrak Nephrops fishery

  • Published source details Frandsen R.P., Holst R. & Madsen N. (2009) Evaluation of three levels of selective devices relevant to management of the Danish Kattegat–Skagerrak Nephrops fishery. Fisheries Research, 97, 243-252

Actions

This study is summarised as evidence for the following.

Action Category

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

Action Link
Marine Fish Conservation

Fit mesh escape panels/windows to a trawl net

Action Link
Marine Fish Conservation
  1. Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

    A replicated, controlled study in 2005 of a seabed area in the Skagerrak and Kattegat, northern Europe (Frandsen et al. 2009) found that fitting a rigid size-sorting escape grid to prawn trawl nets reduced the catches of larger-sized fish of all species but increased the retention of small cod Gadus morhua and haddock Melanogrammus aeglefinus, compared to a standard diamond mesh codend without a grid. Overall, total catch numbers of legal sizes of eight of eight fish species (see paper for full list of species and minimum landing sizes) were lower in the net with a grid (with: 1–229 fish, without: 57–3,283 fish) (data not statistically tested). Catch numbers were significantly lower for cod, haddock, whiting Merlangius merlangus and plaice Pleuronectes platessa smaller than legal size but longer than 25, 20, 17 and 22 cm, respectively (data not reported). Numbers of fish were significantly higher in the net with a grid for small sizes of cod between 10–19 cm and haddock between 11–15 cm (data not reported). In addition, retention of the target prawn species Nephrops norvegicus longer than 41.8 mm was significantly lower with a grid than without (data presented as retention probability curves). In September and October 2005, trials were done by commercial fishing vessel using twin-trawl net gear. Trawl deployments were carried out with a small mesh (40 mm) codend paired with either: a standard 90 mm diamond-mesh codend fitted with a steel grid (22 hauls) or a standard 90 mm unmodified codend (18 hauls). The grid was 35 mm bar spacing in the lower quarters and 80 mm spacing in the upper quarter (see paper for specifications). Catches in each codend were sorted by species and weighed. Total length was measured for commercially important fish species and carapace length for Nephrops.

    (Summarised by: Natasha Taylor)

  2. Fit mesh escape panels/windows to a trawl net

    A replicated, controlled study in 2005 of a seabed area in the Skagerrak and Kattegat, northern Europe (Frandsen et al. 2009) found that fitting a square mesh escape panel to a prawn trawl net did not typically reduce the catches of undersized fish or improve the size-selection, compared to a standard diamond mesh codend without a panel. Overall, the total catches of six of seven fish species (see paper for species tested) below their respective minimum landing sizes were lower in the net with a square mesh panel (with: 68–433 fish, without: 77–747 fish) but a significant reduction was reported only for haddock Melanogrammus aeglefinus. The length at which fish had a 50% chance of escape was higher in nets with a square mesh panel for haddock Melanogrammus aeglefinus (with: 43.8 cm, without: 22.9 cm), similar for five fish species (with: 18.2–34.5 cm, without: 22.3–26.1 cm) and lower for plaice Pleuronectes platessa (with: 18.8 cm, without: 21.9 cm). There was no difference in selection length for catches of the target prawn Nephrops norvegicus between nets (with: 23.6 mm, without: 27.1 mm). In September and October 2005, trials were done by commercial fishing vessel using a twin-trawl net. Paired hauls were carried out with a control small mesh (40 mm) codend paired with either: a standard 90 mm diamond-mesh codend modified with a 120 mm square mesh panel or a standard 90 mm unmodified codend. For each comparison, 18 hauls were completed. All catches were sorted by species and weighed. Total lengths were measured for commercially important fish species and carapace length for Nephrops.

    (Summarised by: Natasha Taylor)

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