Roger B. Larsen

Reduction of fish by-catch in shrimp trawl using a rigid separator grid in the aft belly

Abstract In 1989 and 1990, a new concept to avoid the by-catch of fish in a shrimp trawl was developed in Norway. The system consists of a rectangular aluminium grid with longitudinal bars. The grid is installed in the extension piece, just in front of the codend, angled 48°, with a fish outlet on the top. In front of the grid a guiding funnel or flapper is mounted. Investigations into different grid sizes, bar distances, size of fish outlets, and guiding funnel or flapper constructions during practical tests, have led to several recommended measures. Smaller coastal shrimpers should use grids at least 0.7 m wide and 1.40 m long, while the bigger offshore trawlers should use a 1.0 m wide and 1.5 m long grid, both with a recommended bar separation of 19 mm, which gives an acceptable shrimp loss below 5%. RCTV-observations of the sorting grid system during fishing have shown that most of the shrimps (Pandalus borealis) passed in a straight line through the grid, while fish were guided upwards towards the fish outlet, either by swimming in front of the grid, or sliding along the bars. Some of the smaller fish passed through the grid and ended up in the codend. A combined speed and angle sensor, mounted just behind the grid, measured the horizontal speed of water through the grid to be 0.7 of the towing speed, and the angle of the grid to be 3–5° less than the theoretical mounting angle of 48°. The separator grid allowed an increasing escape of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) up to a length of 20 cm, whereby all fish escaped. The 100% escape lengths for redfish (Sebates sp.), long rough dab (Hippoglossoides platessoides), and polar cod (Boreogadus saida) were 18, 24 and 24 cm, respectively. The Greenland halibut (Reinhardtius hippoglossoides) gave a rather high 100% escape length of 30–32 cm, probably due to the behaviour of this flatfish which swims on its side. The handling of the separator system has so far caused only minor problems, and the pre-sorting of fish by the separator grid results in less sorting work on deck. The separator grid was made compulsory in the northern coastal shrimp fishery from 1 March 1990, from 1 January 1992 in the offshore fisheries and will be compulsory in the Barents Sea and Spitsbergen waters from 1 January 1993.

Use of transparent netting to improve size selectivity and reduce bycatch in fish seine nets

Strategically placed panels of transparent mesh improved the size selection of targeted commercial species (primarily sand whiting, Sillago ciliata) and reduced the bycatch of other species in an estuarine fish seine net. A cover net was placed over the whole bunt and cod-end to quantify the numbers and sizes of fish that passed through the modified and conventional (control) nets. The average size of sand whiting caught in the modified net was larger than in the control net, but other commercial species (sea mullet, flat-tail mullet and silver biddy) showed only a slight change in size selectivity, possibly due to differing escape responses to visual cues. The cover net used in the study appeared to modify the effectiveness of the transparent panels, with some smaller fish observed to re-enter the main net as hauling ceased. An alternative analysis which treated the data as a series of paired comparisons showed an even greater increase in the selection of larger sand whiting than that obtained in the cover net analyses. The panels of transparent netting tested in this experiment show potential as a means of improving the selectivity of fish seine nets.

Performance of the Nordmøre Grid in Shrimp Trawling and Potential Effects of Guiding Funnel Length and Light Stimulation

AbstractThe introduction of the Nordmore 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 Nordmore 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 Nordmore 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...

Escape rate for cod (Gadus morhua) from the codend during buffer towing

The high abundances of Northeast Arctic cod (Gadus morhua) in the Barents Sea have led to 9 the development of a new fishing tactic called buffer towing. On factory trawlers, the trawl is 10 deployed immediately after taking the catch onboard, a tactic used to ensure a continuous 11 supply of fish is being processed. If the desired amount of fish is caught before the catch from 12 the previous haul has been fully processed, the trawl is lifted off the seabed and towed at a given 13 depth at low speed. This is called buffer towing. Cod that escape from the codend when the 14 trawl is shallower than the initial fishing depth are exposed to an increased likelihood of 15 barotrauma-related injuries, increased disease susceptibility, and predation, which could be 16 lethal, or affect growth and reproduction capability. Therefore, this study quantified the escape 17 rate and size selectivity during buffer towing of cod. A new analytical method was applied that 18 allows using the same trawl configuration as applied during commercial fishing and avoids 19 potential bias in the assessment of buffer towing size selection. Our results demonstrated a 20 significant size selection for cod during buffer towing where cod measuring up to at least 42 21 cm in length were proven to escape. In particular, at least 60% of cod measuring 20 cm were 22 estimated to escape during buffer towing. For cod measuring 30 cm and 40 cm, at least 53% 23 and 45% were estimated to escape during buffer towing, respectively. 24

Combination of a sorting grid and a square mesh panel to optimize size selection in the North-East Arctic cod (Gadus morhua) and redfish (Sebastes spp.) trawl fisheries

Combination of a sorting grid and a square mesh panel to optimize size selection in the North-East Arctic cod (Gadus morhua) and redfish (Sebastes spp.) trawl fisheries Manu Sistiaga*, Bent Herrmann, Eduardo Grimaldo, Roger B. Larsen, Leonore Olsen, Jesse Brinkhof, and Ivan Tatone SINTEF Ocean, Brattørkaia 17C, N-7010 Trondheim, Norway The Arctic University of Norway UIT, Hansine Hansens veg 18, 9019 Tromsø, Norway SINTEF Nord, Storgata 118, N-9008 Tromsø, Norway *Corresponding author: tel: þ479 166 3499; e-mail: manu.sistiaga@sintef.no.

Sequential codend improves quality of trawl-caught cod

Trawl-caught fish are frequently associated with deteriorated catch quality. This study presents a new dual sequential codend concept with the aim of improving the quality of trawl-caught fish by minimizing the frequency and severity of catch damage. During towing, the fish are retained in an anterior codend segment with the legislated mesh size. A quality improving codend segment, is attached to the aft part of the first codend segment. Its entrance is closed during the towing phase and opened at a predefined depth during haul-back. Comparing the quality of cod (Gadus morhua L.) retained in the sequential codend with cod caught in a conventional codend, demonstrated a significant improvement in the catch quality, i.e. reduction in catch damages. Cod caught in a conventional codend had only a 3.6% probability of being without visually detectable catch damage. The probability for catching cod without catch damage was five times higher when using the dual sequential codend. Furthermore, cod caught in the sequential codend had a significantly reduced probability of incurring specific catch damage, such as gear marks, poor exsanguination, ecchymosis, and skin abrasions.

New approach for modelling size selectivity in shrimp trawl fisheries

New approach for modelling size selectivity in shrimp trawl fisheries Roger B. Larsen*, Bent Herrmann, Manu Sistiaga, Jesse Brinkhof, Ivan Tatone, and Lise Langård The Arctic University of Norway UIT, Hansine Hansens veg 18, 9019 Tromsø, Norway SINTEF Fisheries and Aquaculture, Brattørkaia 17C, N-7010 Trondheim, Norway Norwegian Directorate of Fisheries, Postbox 185 Sentrum, 5804 Bergen, Norway *Corresponding author: tel: þ4777644536; fax: þ4777646020; e-mail: roger.larsen@uit.no These authors equally contributed to this study.

Fishing efficiency of biodegradable PBSAT gillnets and conventional nylon gillnets used in Norwegian cod (Gadus morhua) and saithe (Pollachius virens) fisheries

Fishing efficiency of biodegradable PBSAT gillnets and conventional nylon gillnets used in Norwegian cod (Gadus morhua) and saithe (Pollachius virens) fisheries Eduardo Grimaldo*, Bent Herrmann, Jørgen Vollstad, Biao Su, Heidi Moe Føre, Roger B. Larsen, and Ivan Tatone SINTEF Ocean, Brattørkaia 17C, N-7010 Trondheim, Norway UiT, The Arctic University of Norway, Breivika, N-9037 Tromsø, Norway *Corresponding author: tel: þ 4740624014; e-mail: Eduardo.Grimaldo@sintef.no. The first two authors contributed equally to this work.

Coincident Mass Occurrence of Gelatinous Zooplankton in Northern Norway

In autumn 2015, several sources reported observations of large amounts of gelatinous material in a large north Norwegian fjord system, either caught when trawling for other organisms or fouling fishing gear. The responsible organism was identified as a physonect siphonophore, Nanomia cara, while a ctenophore, Beroe cucumis, and a hydromedusa, Modeeria rotunda, were also registered in high abundances on a couple of occasions. To document the phenomena, we have compiled a variety of data from concurrent fisheries surveys and local fishermen, including physical samples, trawl catch and acoustic data, photo and video evidence, and environmental data. Because of the gas-filled pneumatophore, characteristic for these types of siphonophores, acoustics provided detailed and unique insight to the horizontal and vertical distribution and potential abundances (~0.2-20 colonies∙m-3) of N. cara with the highest concentrations observed in the near bottom region at ~320 m depth in the study area. This suggests that these animals were retained and accumulated in the deep basins of the fjord system possibly blooming here because of favorable environmental conditions and potentially higher prey availability compared to the shallower shelf areas to the north. Few cues as to the origin and onset of the bloom were found, but it may have originated from locally resident siphonophores. The characteristics of the deep-water masses in the fjord basins were different compared to the deep water outside the fjord system, suggesting no recent deep-water import to the fjords. However, water-masses containing siphonophores (not necessarily very abundant), may have been additionally introduced to the fjords at intermediate depths, with the animals subsequently trapped in the deeper fjord basins. The simultaneous observations of abundant siphonophores, hydromedusae, and ctenophores in the Lyngen-Kvaenangen fjord system are intriguing, but difficult to provide a unified explanation for, as the organisms differ in their biology and ecology. Nanomia and Beroe spp. are holopelagic, while Modeeria rotunda has a benthic hydroid stage. The species also have different trophic ecologies and dietary preferences. Only by combining information from acoustics, trawling, genetics, and local fishermen, were the identity, abundance, and the vertical and horizontal distribution of the physonect siphonophore, Nanomia cara, established.

Trawl Selectivity in the Barents Sea Demersal Fishery

This chapter provides a general overview of the Barents Sea demersal trawl fishery. First, it reviews historical catch levels and current biomass status of four commercially important demersal species (cod, haddock, Greenland halibut, and redfish) and includes an overview of their management plan that has been carried out by the Joint Norwegian–Russian commission. Then, it presents the evolution of the technical regulations for improving size selectivity in this fishery and describes current challenges in gear selectivity. Later, this chapter describes the concept of size selectivity, introduces the selective parameters that define a selection curve, and progressively introduces different parametric models that describe the selection process. The most common experimental methods and gear used to collect selectivity data are described, and their advantages and disadvantages are discussed. Finally, this chapter describes an alternative, or a complementary method, to the conventional estimation of trawl selectivity—the FISHSELECT method. This method is based on morphology measurements and fish penetration models to estimate the selective properties of different mesh shapes and sizes at different mesh openings, which are later used to provide simulation-based prediction of size selectivity. FISHSELECT has already been applied to four important species of the Barents Sea Demersal Fishery, and the results have in all cases showed to be coherent with the results obtained from sea trial results.