Evaluation of separator grates for reduction of bycatch in the silver hake (Merluccius bilinearis) otter trawl fishery off Nova Scotia, Canada

Published source details Halliday R.G. & Cooper C.G. (1999) Evaluation of separator grates for reduction of bycatch in the silver hake (Merluccius bilinearis) otter trawl fishery off Nova Scotia, Canada. Fisheries Research, 40, 237-249.
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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, controlled study in 1992–1993 of three fished areas of seabed on the Scotian Shelf, Atlantic Ocean, Canada (Halliday & Cooper 1999) reported that changing the configuration of size-sorting escape grids (grid angle, bar orientation and increased spacing, guiding device) in small-mesh fish trawl nets did not appear to improve the overall escape of unwanted saithe Pollachius virens and haddock Melanogrammus aeglefinus, compared to a standard grid configuration. Data were not tested statistically. Percentage escapement (by weight) of saithe in modified grid configurations ranged between 43–92%, and for the standard grid escapement was 95–98%. For haddock, escapement in modified grid configurations was 62–100%, and with the standard grid it was 85–94%. In addition, escapement of the commercial target species, silver hake Merluccius bilinearis, was 1–43% with modified grid configurations and 2–5% with the standard grid. Data were collected from three experimental fishing trials on one research vessel and two commercial vessels in June 1992 and May and June 1993. Grids modified with different bar spacings (40 and 50 mm), angles (25° and 45–50°), bar type (vertical or horizontal) and guiding devices (with panel/funnel or without) were tested against a ‘standard’ grid of 40 mm vertical bar spacing, installed at 45–60° angle and with a guiding funnel in front of it (see paper for full specifications). A second (top) codend was attached over the escape opening above the grid to collect the fish escaping from it. A total of 81 deployments (1-3 h duration) were made.

(Summarised by: Chris Barrett)