Abstract
The introduction of the Nordmøre grid to shrimp trawls has reduced the issue of bycatch to that of small-sized species and juveniles that are able to pass through the grid and enter the small-meshed cod end together with the targeted shrimp. This study estimated the size- and species-selective performance of the Nordmøre grid in the configuration most often applied by fishermen and made a preliminary exploration of the effects of reducing the length of the guiding funnel in front of the grid and mounting light-emitting diodes (LEDs) around the escape exit. Experimental fishing trials were conducted in the Barents Sea to assess the size-selective properties of a 19-mm bar spacing Nordmøre grid, mandatory in this Norwegian trawl fishery targeting deepwater shrimp Pandalus borealis (also known as northern shrimp), and its potential improvement. Results were obtained for the target species and four bycatch species: redfish Sebastes spp., Haddock Melanogrammus aeglefinus, Atlantic Cod Gadus morhua, and American Plaice Hippoglossoides platessoides. In general, very few deepwater shrimp were found to escape through the escape exit, although the quantity increased slightly at larger sizes. Between 80% and 100% of the bycatch species up to a species-specific size passed through the grid and entered the cod end. A short guiding funnel decreased this for Haddock significantly by increasing the fraction of small Haddock seeking the escape exit. Further, adding LEDs around the escape exit significantly negated this effect. For the other bycatch species, the results indicated similar trends but were not statistically significant. However, considering that only a few fishing hauls were conducted using the short guiding funnel with or without mounting LEDs calls for some caution when attributing these changes to the configuration of the Nordmøre grid, and these preliminary results should be followed up by further testing before definitive conclusions are made.
Highlights
Regarding the number of bycatch fish species, a total of 9,090 redfish, 1,529 Haddock, 1,158 Atlantic Cod, and 15,206 American Plaice Hippoglossoides platessoides were measured (Table 1). This means that the study is based on a total of 38,583 shrimp and fish measurements (25,624 of which were from the configuration most often applied in the fishery), while 8,752 and 8,509 measurements were taken for the short funnel and short funnel + light-emitting diodes (LEDs) configurations, respectively (Table 1)
This study investigated the performance of the Nordmøre grid in the gear configuration most often used by fishermen targeting deepwater shrimp in the Barents Sea
It further made a preliminary exploration on the effect of shortening the guiding funnel length and mounting LEDs around the escape exit on the performance of the Nordmøre grid
Summary
Fishing areas are closed if catches of 10 kg of deepwater shrimp contain more than 8 Atlantic Cod Gadus morhua, 20 Haddock Melanogrammus aeglefinus, 3 redfish Sebastes spp., or 3 Greenland Halibut Reinhardtius hippoglossoides (Norwegian Directorate of Fisheries 2011) These relatively strict bycatch rules have led to frequent closures of large shrimp fishing grounds in the northeastern Atlantic Ocean over the last few years. Grimaldo et al (2015) showed that guiding fish to a sizeselective sorting grid by means of a guiding panel is essential for achieving satisfactory selectivity results for species such as Atlantic Cod. One factor that can affect this contact ratio is the length of the guiding funnel, which is intended to ensure that the majority of the targeted deepwater shrimp make contact with the Nordmøre grid and are sorted into the cod end. Other species such as flatfish (order Pleuronectiformes), which are similar to Atlantic Cod in that they tend to stay low down inside the trawl, can pose a challenge when it comes to facilitating their escape through exits placed in the upper panel of the gear
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