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

The effectiveness of separator grates in reducing bycatches in the small-mesh otter trawl fishery for silver hake on the Scotian Shelf was examined in three experiments aboard a research and two commercial vessels. Different grate bar orientations, bar spacings, grate insertion angles, and guiding mechanisms were tested. The size selection and escapement levels resulting from these grate configurations are described. A grate with vertical bars spaced 40 mm apart inserted at 45–60°, and with a funnel or panel forward of the grate to direct fish to its base, released 85–98% by weight of pollock and haddock, and 48–70% of other species, while retaining 95% of silver hake. Commercial bycatches contained more small haddock than did experimental catches, and it is projected that commercial use of this grate would release 75–80% by weight of haddock encountered, and only 50% by number. Other grate configurations tested displayed poorer species selection characteristics.