Effectiveness of the Nordmore grate in the Gulf of Maine Northern shrimp fishery

The Nordmore grate is a by-catch excluder device that has been required in the Gulf of Maine Northern shrimp Pandalus borealis trawl fishery since April 1992. We evaluated the effectiveness of the Nordmore grate in the Gulf of Maine Northern shrimp fishery using data collected by fishery observers before and after the Nordmore grate was required. The percentage of by-catch (kg) in observed tows declined from nearly 50% before the Nordmore grate was required to about 15% after the Nordmore grate was required. The Nordmore grate significantly (P ≤ 0.001) reduced by-catch (kg/h) of eight of nine groundfish species examined and of two species groups (flatfish and roundfish). However, the magnitude of the reductions in the fishery was about 35% less than obtained in controlled experimental studies in the Gulf of Maine [Kenney, J.F., Blott, A.J., Nulk, V.E., 1992. Experiments with a Nordmore grate in the Gulf of Maine shrimp fishery. In: Proceedings of the Marine Technology Society Conference, pp. 328–335]. Catch rates of Northern shrimp (kg/h) increased using the Nordmore grate (+37%) possibly due to higher catch rates of large shrimp.