Effects of a geophysical survey on catching success in longline fishing

The effects on longline catches of a geophysical survey conducted during the winter fishery for cod (Gadus morhua) were studied. Spatial extent of the effects was investigated by comparing the catch rates of longlines set at various distances from the survey tracklines, and duration of the effects was studied by analysing the catch rates of longlines soaked after the sound emissions ended. Catch reduction of 55-80% was observed for longlines set within the seismic survey area. The results indicated that the acoustic device used caused a 24-h duration and 5-miles spatial extent of reduced catches

Effects of setting time, setting direction and soak time on longline catch rates

Most studies of factors affecting catching efficiency and selectivity in longlining have focused on various gear parameters (mainline and snood material, hook design and size, rigging) and on the bait (type and size), and few studies have investigated how catch rates are affected by the way the gear is operated during fishing. We carried out fishing experiments to study the effects of setting time, setting direction (relative to the current direction) and soak time on catch rates of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Lines set before dawn and lines set across the current gave higher catch rates of haddock than lines set after dawn and in the same direction as the current, respectively. Similar effects were not found for cod, and these differences between haddock and cod were explained by differences in behaviour and interspecific competition for the available baits. Soak time was not found to significantly affect the catch rates of either species, indicating that other factors have a more pronounced effect on longline catch rates and may therefore mask the effect of soak time

Reflex impairment as a measure of vitality and survival potential of Atlantic cod (Gadus morhua)

A ssur ing the v itality and survival potential of live-caught Atlantic cod (Gadus morhua) is important for improving the sorting of fish before net penning operations designed to hold fish for growth and later market. When Atlantic cod are captured by Danish seine, the most commonly used fishing gear for live-caught fish, they undergo stressors such as forced swimming, net abrasion, and air exposure. Laboratory experiments (at an air temperature of 9°C and water temperature of 8°C) were conducted with the aim of constructing a RAMP (reflex action mortality predictor) curve for prediction of vitality and survival potential in Atlantic cod captured in Danish seines, by varying the levels of these stressors. Atlantic cod exposed to increased duration in air (5–20 min) showed increased reflex impairment and mortality, with 75% mortality at 10 minutes of air exposure. Forced swimming in combination with net abrasion and air exposure did not increase reflex impairment or mortality above that associated with air exposure alone. The Atlantic cod RAMP curves indicated that fish with reflex impairment less than 50% would not show mortality and would likely recover from capture stress

Sammenligning mellom newfoundlandteine og tokammerteine

Sluttrapport til FHF: Prosjekt 900702The main objective of the project was to compare the catching efficiency of the Norwegian to-chamber pot and the Canadian Newfoundland pot. Two fishing trials were carried out and both showed that the two-chamber pot gave higher catch rates for cod and tusk. Two-chamber pots set on the bottom had higher catches compared to pots floated off the bottom, and pots baited with squid were more efficient than pots baited with herring. Bottom set two-chamber pots baited with squid and set across-current gave mean catches of cod of 35 kg (6.3 fish) per pot. Based on these and earlier results, a proposal with the objective to develop a cost-effective pot fishery for cod and tusk has been submitted to the Norwegian Research Counci

Reduced bycatch of red king crab (Paralithodes camtschatica) in the cod gillnet fisheries in northern Norway: Fishing trials with norsel mounted gillnets

Bycatch of red king crab (Paralithodes camtschatica) in stationary fishing gears, q&ally gillnets, is an increasing problem to the inshore fishermen in the northern part of Norway (Finnmark county). The results are large bycatches of king crabs together with the crabs’ damages on the gear and catch. In the cod gillnet fisheries, the problem might be solved by using specially made gillnets (“norsel-mounted” nets) where the net itself is floated 0.5 meters above the seabed. The norsel-mounted nets were compared with standard nets in the Varangerfjord (eastern Finnmark) in the period 17 March - 28 May 1999. The trials showed that norsel nets needed more floats than the standard nets to get the net to stand properly in the sea (to get the norsels stretched out suitably). By using extra float (rings) on the norsel mounted nets the bycatches of king crab were reduced to an acceptable level with an average of 0.6 crabs/net, compared with 3.3 crabs/net on standard and 6.7 crabs/net on nor-se1 nets without extra float. Norse1 nets caught only about l/3 as many fish as standard nets. The catch results indicated that the gear configuration functioned in order to reduce the bycatch of red king crab. Loss of fish up to 65% is, however not satisfying. Further work is needed to find a solution that gives a minimal loss of fish. Knowledge about the different species’ behaviour is of importance in the further development of a more selective gear

Fangst av leppefisk: Ruse gir like god overlevelse som teine

Leppefisk er viktig i oppdrettsnæringens lakselusebekjempelse. I 2010 ble det fanget ca. 10 millioner leppefisk til dette formålet. Det blir hevdet at teiner gir fisk av bedre kvalitet enn ruser, og enkelte oppdrettsselskaper kjøper kun leppefisk fanget med teiner. Et forsøk der vi sammenlignet overlevelsen viste imidlertid ingen forskjell mellom de to redskapstypen

Surface selection of haddock and cod in the Norwegian demersal seine fisheries

Size selection in active fishing gears is a continuous process and undersized fish may escape during the whole fishing operation. Fish that escape during the surface hauling operation are likely to experience higher mortality due to barotrauma-related stress than fish escaping at the fishing depth during the towing process. A well-functioning selectivity device should therefore select mostly at depth for enhancing survival probabilities of escaping fish. The current gear regulation in the Norwegian demersal seine fishery is likely to cause large proportion of undersized fish to escape at the surface. In this study, we estimated surface selection of haddock and cod in demersal seine by using an automatic release system and a small meshed codend that collected fish escaping during surface hauling. The collecting bag contained 19% undersized haddock compared to 10% in the conventional square-mesh codend indicating that about 50% of undersized haddock brought to the surface were released. The proportions of undersized cod were 8% for the collecting bag and 1% for the conventional square-mesh codend. These results demonstrate that surface selection is significant for both haddock and cod. Based on this finding, we discuss methods to improve size selectivity at the fishing depth.publishedVersio

Selective flatfish seine: A knee-high demersal seine barely catches cod

Norwegian coastal cod (Gadus morhua) protection restricts the use of active fishing gears. Demersal seines, acknowledged as being efficient for targeting flatfish, are therefore largely excluded from the fjords. To exploit plaice (Pleuronectes platessa), a species-selective gear that avoids catching cod is needed. We therefore designed a low-rise demersal seine with a 0.6 m vertical opening and tested it on fishing grounds in Lofoten (Northern Norway), comparing it with a conventional seine that had a vertical opening of ∼3.5 m, and fished both during the day and at night. Six to nine hauls were taken with each of the four gear/time-of-day categories (32 hauls in total). The low-rise seine caught no fewer plaice during day-time fishing, but less at night. Cod and haddock (Melanogrammus aeglefinus) catches were reduced by 94% and 98%, respectively, while catches of sole (Solea solea) increased with the low-rise seine. No catch differences were found for halibut (Hippoglossus hippoglossus), common dab (Limanda limanda), or monkfish (Lophius piscatorius). The low-rise seine therefore enables targeting flatfish while avoiding gadoid catches, although loss of plaice during night-time fishing is to be expected.publishedVersio