Understanding sorting grid and codend size selectivity of Greenland halibut (Reinhardtius hippoglossoides)

Published source details Herrmann B., Sistiaga M., Larsen R.B., Nielsen K.N. & Grimaldo E. (2013) Understanding sorting grid and codend size selectivity of Greenland halibut (Reinhardtius hippoglossoides). Fisheries Research, 146, 59-73.
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This study is summarised as evidence for the following.

	Action	Category
	Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water) Action Link

Use a different design or configuration of size-sorting escape grid/system in trawl fishing gear (bottom and mid-water)

A replicated study in 1994–2011 of two seabed areas in the Norwegian and Barents Sea, Norway (Herrmann et al. 2013) found that two different types of commercially used size-sorting escape grid systems in fish trawl nets had different size-selectivities for unwanted Greenland halibut Reinhardtius hippoglossoides. The length at which halibut had a 50% chance of escaping through the grid (fish >30 cm only) was greater with a ‘Sort-V’ grid system compared to a ‘Sort-X’ grid system (Sort-V: 59–67 cm, Sort-X: 42–56 cm). In addition, it was found that this may be due to differences in the body orientation of halibut between grids to give the optimum angle for escape. Two sets of trials were conducted on different vessels, fishing in separate areas and with different trawl gears in November 1994 and October 2011. In 1994, four deployments were done on fishing grounds near Tromsøflaket using a trawl net fitted with a ‘Sort-X’ escape grid system, consisting of two grid sections and a canvas guiding section. In 2011, six deployments were completed on the banks of Hopendjupet, using a Sort-V grid system comprising one grid attached to a mesh guiding panel behind a mesh lifting panel (see paper for gear specifications). For both grid systems, the grid had 55 mm bar spacing, and halibut escaping from them were collected in mesh covers installed over the escape openings. Codends were fitted with a small-mesh inner bag to sample retained fish. Halibut from the cover and codend catches were counted and length measured.

(Summarised by: Natasha Taylor)