Survival of mackerel and saithe that escape through sorting grids in purse seines

Published source details Misund O.A. & Beltestad A.K. (2000) Survival of mackerel and saithe that escape through sorting grids in purse seines. Fisheries Research, 48, 31-41.
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This study is summarised as evidence for the following.

	Action	Category
	Fit escape devices (panels/grids) to encircling nets Action Link

Fit escape devices (panels/grids) to encircling nets

A replicated, controlled study in 1993–1995 at four coastal pelagic sites in the North Sea/Norwegian Sea, Norway (Misund & Beltestad 2000) found that using a rigid size-sorting escape grid in a purse seine net resulted in no difference in the survival of saithe Pollachius virens that had escaped through the grid, but survival of mackerel Scomber scombrus appeared reduced, compared to fish that did not pass through a grid. These results were not tested for statistical significance. Survival of saithe one month after capture was 97–100% for fish following use of an escape grid and 100% for fish that had not been through an escape grid. However, mackerel survival one month after capture was 18–56% for grid-escaped fish and 45–95% for fish that had not been through an escape grid. Three mackerel fishing trials were done by chartered purse seiners in August-September 1993–1995 at three coastal sites. Two saithe trials were done at one coastal site in April 1994 and by research vessel. Mackerel or saithe were captured by purse seine nets and towed inshore to large net pens. Fish that had passed through an escape grid were separated from fish that were caught in purse seine nets without grids. For mackerel, a 10 m² metal grid with 42 mm bar spacing was fitted to the seine net and for saithe a 1 × 2 m² glass fibre reinforced polyester grid with 30 mm bar spacing was fitted. As the nets were hauled in, fish escaping through the grids were collected in separate net pen. Across all trials, numbers of grid-escaped fish were 16,285 mackerel and 7,848 saithe. Fish that did not pass through an escape grid numbered 37,775 mackerel and 25,463 saithe. Survival was recorded weekly for a month.

(Summarised by: Natasha Taylor)