Study

The use of separator panels and square mesh windows for by-catch reduction in the crustacean trawl fishery off the Algarve (South Portugal)

  • Published source details Campos A. & Fonseca P. (2004) The use of separator panels and square mesh windows for by-catch reduction in the crustacean trawl fishery off the Algarve (South Portugal). Fisheries Research, 69, 147-156

Actions

This study is summarised as evidence for the following.

Action Category

Use a separator trawl

Action Link
Marine Fish Conservation

Modify the configuration of a mesh escape panel/window in a trawl net

Action Link
Marine Fish Conservation
  1. Use a separator trawl

    A replicated study in 1993–1994 of an area of seabed in the Atlantic Ocean off the coast of Portugal (Campos & Fonseca 2004) found that shrimp trawl nets combining a separator panel with a square mesh escape window reduced the catch of one of two unwanted fish species, compared to a square mesh window alone. Overall, the percentage escape of boarfish Capros aper was higher by 10–44% (105–1,430 kg) from nets with a separator panel compared to 17% (896 kg) with no panel and amounts of escaped blue whiting Micromesistius poutassou were similar (67–81%; panel: 58–187 kg, no panel: 107 kg). In addition, the escape rates of boarfish increased with increasing mesh size of the square mesh panel (70 mm: 10%, 100 mm: 44%). Escaped catch of the target species rose shrimp Parapenaeus longirostris and Norway lobster Nephrops norvegicus was <1–28% in nets with panels compared to 1–24% with no panel. Four fishing trials were undertaken, each testing one of four trawl nets: three with different separator panel/escape window mesh size combinations and one with the window alone (see paper for specifications). For each net, six or seven experimental hauls were conducted in July 1993 to May 1994 off the Algarve coast. Fish and crustaceans that escaped through the square mesh window were collected in a small mesh cover mounted over the escape window. Codend (top and bottom) and cover catches were sorted by species, weighed and lengths recorded.

    (Summarised by: Natasha Taylor)

  2. Modify the configuration of a mesh escape panel/window in a trawl net

    A replicated, paired study in 1993–1994 of a seabed area in the Atlantic Ocean off Portugal (Campos & Fonseca 2004) found that increasing the mesh size of a square mesh escape window in a shrimp separator trawl net reduced the catch of unwanted boarfish Capros aper, but not horse mackerel Trachurus trachurus and blue whiting Micromesistius poutassou. In trials with a 120 mm separator panel, the escape of boarfish increased with increasing mesh size of the square mesh window, with 42% (1,430 kg) of the overall boarfish catch escaping through a 100 mm window compared to 10% (105 kg) with a 70 mm window mesh size. For horse mackerel, escape percentages were similar between window mesh sizes (100 mm: 33%, 70 mm: 34%). In trials with an 80 mm separator panel and 100 mm mesh escape window, boarfish escape was higher (44%) compared to the 120 mm panel with the smaller 70 mm mesh window, but similar to the 120 mm panel with the same size 100 mm mesh window. There were no differences in escape rates between each panel/window codend for horse mackerel or blue whiting (see paper for data). In addition, there were also no differences in escape rate of all three species between a codend with no panel and a 100 mm window alone, and the 70 mm window in the 80 mm panel codend. Percentage escape of the commercial target species rose shrimp Parapenaeus longirostris and Norway lobster Nephrops norvegicus was similar between mesh sizes with the 120 mm separator panel, however rose shrimp catches varied between the 120 mm and 80 mm mesh panels (see paper for data). Four fishing trials were done in July and September 1993 and May 1994 by research and fishing vessels. In each trial one of four trawl nets was tested: three with different separator panel/escape window mesh size combinations and one with the window alone (see paper for specifications). For each net type, six or seven experimental hauls were done, 26 in total, and catches were retained in the upper and lower codends. Fish escaping through the square mesh window were collected in a small mesh cover mounted over the escape window. Codend and cover catches were sorted by species, weighed and lengths recorded.

    (Summarised by: Natasha Taylor)

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