The sorting grid used in cold-water prawn fishing ensures low by-catches
The mandatory use of sorting grids in prawn trawlers ensures very low by-catches in prawn fishing in Greenland.
Prawns are found close to the seabed, together with many other fish species and as a species, prawns are smaller than most. Prawn fishing in West Greenland takes place on the Greenlandic continental shelf, at a depth of 300-600 m. Here, the prawns are found in specific areas, typically on a soft bed of mud and sand. Usually, the same areas are fished, year after year.
Trawls are normally used for prawn fishing because a small mesh size is necessary. The mesh size of the netting in the codend is at least 40 mm. For comparison, the mesh size is 100 mm for Greenland halibut fishing. The trawl is towed just above the seabed, with a risk of netting other species as by-catches that can be both large and small, below the minimum size. This includes cod, Greenland halibut and Atlantic wolffish. The trawlers should not be loaded with any other species than prawns, as this is the target species and production is designed for this purpose.
Prawns are found in East and West Greenland, in both coastal and offshore habitats. The primary fishing areas in West Greenland are currently off Nuuk and in more northern areas. Trawl fishing takes place in both zones, but there are limitations to the size of the vessels permitted to fish in close proximity to the coast. Species diversity diminishes as we move northwards, so that by-catches are generally very limited in cold-water prawn fishing in Greenland, compared to southern regions, such as Europe.
Introduction of prawn grids
Back in the 1980s, the first attempts to insert a grid into the trawl, in order to eliminate unwanted species, were made in Norway. When the grid proved to be functional, it was further developed and today is known as the Nordmøre grid. In 2001, Greenland introduced legislation requiring prawn grids to be used in the trawls on all vessels. For health and safety reasons, however, an exemption was granted for coastal vessels. This exemption was removed in 2011, and today all prawn trawlers use sorting grids.
The sorting grid was well-received by most fishermen, since it eliminated manual catch sorting, while larger fish might squeeze the prawns, and overall resulted in more efficient fishing and prawns of better quality. The sorting grid is thus of major benefit to fishermen, while also protecting other species and thereby also the ecosystem.
The grid is designed as a barred grid and under Greenlandic legislation, the space between the bars must be at least 22 mm. This means that fish, and anything else larger than 22 mm, are "pushed" back out of the trawl, while the smaller prawns pass through the grid and are caught. The sorting grid is placed at the end of the trawl, at the entrance to the codend. Above it, there is a hole through which the rejected fish are released back into the sea.
The introduction of the grid has reduced by-catches considerably. The grid serves to eliminate large and small species, including large fry, that were previously retained in the codend. However, anything shorter or narrower than 22 mm can still end up in the codend. This might include smaller fish species such as polar cod and crustaceans (krills). These will be rejected in the fish separator on board the vessel.
Each year, by-catch volumes are compiled by Greenland’s Fisheries Licence Control Authority (GFLK) and for many years the by-catch level has been <1% of the total catch. This is very low and confirms the sorting grid's effectiveness. The very low by-catch level is also one of the cornerstones of the MSC certification of prawn fishing in West Greenland.
The grid is continuously refined and adapted to current needs. The bar spacing must match the size of the prawns, as well as any possible by-catches in the specific fishing grounds. The working environment must also be arranged to ensure optimum handling, to protect the health and safety of the crew.