Manu Sistiaga

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

How many fish need to be measured to effectively evaluate trawl selectivity

The aim of this study was to provide practitioners working with trawl selectivity with general and easily understandable guidelines regarding the fish sampling effort necessary during sea trials. In particular, we focused on how many fish would need to be caught and length measured in a trawl haul in order to assess the selectivity parameters of the trawl at a designated uncertainty level. We also investigated the dependency of this uncertainty level on the experimental method used to collect data and on the potential effects of factors such as the size structure in the catch relative to the size selection of the gear. We based this study on simulated data created from two different fisheries: the Barents Sea cod (Gadus morhua) trawl fishery and the Mediterranean Sea multispecies trawl fishery represented by red mullet (Mullus barbatus). We used these two completely different fisheries to obtain results that can be used as general guidelines for other fisheries. We found that the uncertainty in the selection parameters decreased with increasing number of fish measured and that this relationship could be described by a power model. The sampling effort needed to achieve a specific uncertainty level for the selection parameters was always lower for the covered codend method compared to the paired-gear method. In many cases, the number of fish that would need to be measured to maintain a specific uncertainty level was around 10 times higher for the paired-gear method than for the covered codend method. The trends observed for the effect of sampling effort in the two fishery cases investigated were similar; therefore the guidelines presented herein should be applicable to other 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

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.

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.

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.