Bycatch reduction in the Norwegian Deep-water Shrimp (Pandalus borealis) fishery with a double grid selection system

Abstract

Trawlers targeting Deep-water Shrimp (Pandalus borealis) in the North Atlantic use a Nordmøre sorting grid ahead of a small-meshed codend. Based on experimental fishing, the effect of adding a 9 mm spaced release grid behind the mandatory 19 mm spaced Nordmøre sorting grid, was determined. The performance in terms of size selection of the release grid and the two grids combined were assessed for target Deep-water Shrimp and for juvenile Redfish (Sebastes spp.) and American Plaice (Hippoglossoides platessoides), two of the most common bycatch species in the fishery. The aim of using the release grid was to improve the escape of undersized shrimp and the bycatch of juvenile fish from the gear. The results demonstrated that the release grid improved the escape of the smallest Deep-water Shrimp significantly. The fraction of small shrimp released through this grid was estimated to be 45 %. However, the results also revealed the need for further improvements in the design of the release grid to increase the reduction of small shrimp and juvenile fish bycatch. For Redfish and American Plaice the fractions of juveniles escaping through the release grid were estimated to be 16% and 32%, respectively. In addition, the release grid only led to the escape of the smallest juvenile individuals, in particular for Redfish.

Predicting optimal combinations of by‐catch reduction devices in trawl gears: A meta‐analytical approach

“…To push the boundaries of trawl selectivity, recent studies have begun to combine sequential BRDs (Brinkhof, Olsen, Ingólfsson, Herrmann, & Larsen, ; Larsen, Herrmann, Sistiaga, Brinkhof, & Grimaldo, ; Stepputtis, Santos, Herrmann, & Mieske, ). Indeed, a combination of BRDs could be more effective in reducing unwanted catches of multiple species (Larsen, Herrmann, Sistiaga, Brinkhof, et al, ) or even achieving alternative selective profiles for the target ones (Stepputtis et al, ). Despite these few studies, the potential benefit of combining existing BRDs remains still widely unexplored.…”

“…The meta‐analytical approach presented here combines data available on BRDs that have been individually tested within a specific fishery to predict the selectivity of the potential BRD combinations. The theoretical performance and potential applicability of BRD combinations for the fishery are then investigated in terms of differences in size selectivity, catch profile and potential consequences on fishermen's incomes (Larsen, Herrmann, Sistiaga, Brinkhof, et al, ; Sala, Lucchetti, Perdichizzi, Herrmann, & Rinelli, ; Veiga‐Malta et al, ) to identify the most promising options.…”

“…To push the boundaries of trawl selectivity, recent studies have begun to combine sequential BRDs (Brinkhof, Olsen, Ingólfsson, Herrmann, & Larsen, 2018;Larsen, Herrmann, Sistiaga, Brinkhof, & Grimaldo, 2018;Stepputtis, Santos, Herrmann, & Mieske, 2016).…”

Testing a size sorting grid in the brown shrimp (Crangon Crangon Linnaeus, 1758) beam trawl fishery

“…Sorting grids have been used as a way to reduce the catch of small shrimps in a northern prawn fishery in Gulf of Maine (He and Balzano, 2007;2012) and Norwegian northern prawn fishery (Larsen et al, 2018). In this study, we demonstrate the ability of a size-sorting grid to reduce the catch of brown shrimp below marketable size.…”

“…Grids are commonly used in shrimp fisheries as bycatch reduction devices (Broadhurst, 2000;Polet, 2002;Graham, 2003;Fonseca et al, 2005). More recently, grids have also been tested for size sorting of the target species in a northern prawn (Pandalus borealis Krøyer, 1838) fishery (He and Balzano, 2012;2013;Larsen et al, 2018). Therefore, the aim of this study was to investigate the size selective performance for brown shrimp, in a dual sequential selectivity system, using a grid with 6 mm bar spacing in combination with a 22 mm diamond mesh codend.…”