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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.

During a 2018 retrieval cruise for abandoned snow crab (Chionoecetes opilio) pots in the Barents Sea, approximately 8600 pots abandoned 1.5 years earlier were recovered. Forty-three percent of a subsample of 1000 pots contained snow crabs, with an average of three crabs per pot. Most of the crabs were alive (~98%) and dominated by large males. Pinch injuries and limb loss were common and tended to decline with increasing crab size. Reflex testing showed that the crabs were vital (i.e. the crabs moved their legs, chelipeds and maxillipeds when stimulated), which was supported by a relatively high meat content. However, energy reserves in the digestive glands (hepatopancreas reserves) were low, indicating overall energy deficiencies. Our results indicate considerable unaccounted mortality due to self-baiting, continued catch and cannibalism. The findings demonstrate that snow crab pots which are lost or abandoned in the Barents Sea fishery maintain huge potential for ghost-fishing impacts.

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.

Recreational fishing is a popular activity around the globe, and fish welfare issues related to the activity have received increasing attention in some countries, particularly in central and northern Europe and Australia. This chapter offers an introduction to recreational fishing, reviews literature on fish welfare in relation to recreational fishing and provides an overview of potential biological impacts and ways to reduce such impacts. We first focus on the question on how to reduce impacts on the welfare of the fish during recreational fishing. Second, we describe two case studies highlighting that practical implications of the fish welfare discourse may be disjointed from the scientific information base and be rather about fundamental moral questions about the ethical acceptability of the activity per se. We end by providing an outlook on the future of recreational fishing in the light of the current fish welfare discourse.

Capture-based aquaculture (CBA) combines aquaculture practices with capture fisheries to keep the catch alive for either short or long periods of time, for feeding or for live storage. CBA enables us to market numerous species ranging from molluscs, scallops and crustaceans to fish such as tuna, cod, eel and groupers. In CBA, handling and adaptation to new environments have an additional influence upon the stressors to which fish are exposed during capture, and the duration of this impact increases dramatically from minutes and hours in traditional fishing to days and months in CBA. We show how a strong focus on welfare is already present in cod CBA fisheries and the rationale behind this focus. We present a case study on CBA of Atlantic cod (Gadus morhua) as a robust example and model species for detecting welfare risks and mitigating against them. We discuss the main welfare issues in relation to the three broad phases of capture, transport and live storage, and identify common current fish welfare challenges in CBA. We highlight the advantages of pursuing this approach using lessons learnt from an industry in which fisheries and aquaculture meet and where an existing and successful knowledge transfer process between fisheries and aquaculture is already under way.

The introduction of catch welfare to commercial wild-capture fisheries will be challenging. In this chapter, we discuss how taking a science-based approach to understanding catch welfare in commercial fisheries could lead to practical solutions to improving welfare that will not only have ethical benefits, but may also have tangible benefits for the fishery, including improved sustainability, product quality and shelf life, and hence profitability. There has been little research to date specifically directed at the development of catch welfare in commercial fisheries. However, there is a substantial and growing body of literature on the fate and vitality of released animals from commercial fisheries—most recently catalysed by the introduction of the Landing Obligation in the EU. Furthermore, there is much to be learned from the aquaculture industry with regard to good welfare practices and product quality, particularly regarding catch handling and slaughter. This chapter utilises this available knowledge to develop a risk assessment-based framework for identifying capture-related stressors and suggests ways of mitigating their impact on the welfare of the catch, as well as on product quality. This framework is developed in context with four contrasting case study capture methods: trawl, purse seine, gill/trammel nets and pots. Finally, it concludes with a summary of the current research priorities and significant strategic challenges for developing welfare-conscious practices in commercial fisheries.

Luminescent netting increases the catch rate of snow crabs (Chionoecetes opilio) over short soak times (1 d), however the commercial fishery often requires longer soak periods, up to1 week. Building on previous research, this study investigated the catch efficiency and size selectivity of pots with luminescent netting over long soak times (144–336 h) in the inshore snow crab fishery of Newfoundland, Canada. A total allowable catch and individual quota allocation management system for snow crab is regulated in Canada and using luminescent netting to increase catch rates would reduce the carbon footprint of the fishery by reducing days fished. Our results showed that luminescent pots had a 21.6 % and 18.3 % higher catch-per-unit-effort (CPUE; number of crabs per pot) of legal-sized crab and sub-legal sized crab, respectively, than control pots; with no difference for soft-shelled crab. Additionally, no significant differences were shown for size selectivity over the range of carapace widths observed between luminescent and control pots. Little other bycatch (female snow crab and unwanted species) were caught in either pot treatments. This study shows that luminescent netting increases the efficiency of the snow crab fishery, which provides economic and environmental benefits.

The use of pots in the north Atlantic finfish fisheries is negligible because this fishing method typically has a low capture efficiency. Large numbers of individuals encounter baited pots, but the proportions of fish that enter the pot and become caught are low. Krill, which constitutes an important prey for cod (Gadus morhua), is attracted by light. The catching efficiency of baited cod pots with three light sources with different colours and intensities (white: 9744 mW m−2, white: 23 mW m−2, green: 8 mW m−2) were tested in coastal waters in northern Norway. Pots with the light source of highest intensity gave a 17 times higher catch rate of cod than that of control pots (with bait only). The light source of medium intensity gave about a five times higher catch rate, whereas the weakest light did not influence the catch. Cod caught in pots with light had more krill and arrowworms in their stomach and were observed feeding on these preys inside the pot. We concluded that light sources of increasing intensity attract more krill, and that cod were attracted into the pot by the dense swarms of prey and not the light per se.

The present study tested whether the presence of already retained fishes inside baited fish pots acted as a social attraction and affected the entrance probability of Atlantic cod Gadus morhua in a fjord in northern Norway. Video analysis revealed that the probability of an entrance initially increased with the presence of low numbers of fishes inside the pot, but subsequently decreased at a critical number of caught fishes. The critical number was dependent on the size of the G. morhua attempting to enter. This demonstrates that social attraction and repulsion play a role in G. morhua pot fishing and has important implications for the capture efficiency of fisheries executed with pots.

The development of low impact and fuel efficient (LIFE) fishing is being paid growing attention. Pot fishing has lower environmental impact and fuel consumption than most other fishing methods. However, pots typically have low capture efficiency for most ground-fish species, and efforts to develop effective commercial pots are needed. Bycatch of red king crab ( Paralithodes camtschaticus ) is a severe problem in the coastal fishery for cod ( Gadus morhua ) in the Barents Sea. In a previous publication, we demonstrated that cod pots floated off the bottom eliminated this problem. Our original bottom-set cod pot has two entrances in order to increase the rate of entry of fish, but when this pot is floated, fish that search for food by following chemical cues up-current will only encounter the entrance that is oriented down-current. We therefore compared the catch rates of floated pots with one and two entrances, and predicted that the new design with only one entrance would achieve higher catch rates due to a lower rate of escape. Pots with one entrance caught significantly more cod and haddock ( Melanogrammus aeglefinus ) than pots with two entrances. The catch rate of cod above minimum landing size (≥44 cm) of pots with one entrance was 82% higher than that of pots with two entrances. Pots that were snagged and did not float properly caught large numbers of king crab. The larger catches of pots with one entrance could be explained by lower escape rate from this design. The observed difference in catch rates between the two pot types indicates that more than 50% of the large cod and haddock that entered the pot with two entrances escaped. There is therefore great potential for increased catching efficiency of pots through improved pot design.

In this study, we investigated luminescent netting as a means to improve the catch rates of snow crabs Chionoecetes opilio. A laboratory experiment was conducted to investigate the intensity and duration of luminescence using time‐lapse photography. We exposed experimental traps to five different treatments of UV light to excite the luminescent fibers in the netting. Our results showed that luminescent netting can be effectively activated to emit light, and that the resulting intensity and duration of luminescence emitted over time depends on the initial duration of UV exposure and the source of light. A fishing experiment was subsequently conducted in eastern Canada to compare the catch rate of traditional and luminescent traps, and to determine how soak time affected catch rate. Results indicate that the effect of luminescent traps on the CPUE (measured as number of crab per trap) depended on the soak time. The CPUE was significantly higher (a 55% increase) in luminescent traps that underwent relatively short soak times (~1 d), but when soak times were longer (~8 d), the CPUE was not significantly different.

Snow crab (Chionoecetes opilio) has become an important species for the Norwegian seafood industry since its first commercial harvest in 2012. However, periodically catch rates can be low, causing a financial strain on the fishery. Thus, improving the catch rate of existing pot designs has the potential to significantly improve the profitability of fishing enterprises. In this study, we investigated whether the addition of low-powered purple and white light-emitting diode (LED) fishing lights inside the pots could improve catch rates of snow crab in the Barents Sea. Results showed that pots with purple lights harvested a 12.8% higher catch per unit effort (CPUE; number of crab per pot) of legal-sized crab, which was significantly more than the control pots (p = 0.035); pots with white lights did not catch significantly more crab (p > 0.05). Pots equipped with only light (no bait) caught very few crabs and were not considered a viable alternative. Although purple LEDs increased snow crab capture, the economic benefits of using underwater lights in pots remains unclear given the high capital investment required.

To increase our understanding of the interaction between fish and baited fishing gear we quantitatively described the behaviour of cod (Gadus morhua), saithe (Pollachius virens), and haddock (Melanogrammus aeglefinus) to baited pots in a fjord in northern Norway. Detailed video analyses were made to describe species specific responses and examine the effect of lifting the pot off the bottom. The majority of both cod and saithe approached the pots in an upstream direction, and fish approached floated pots higher in the water column than bottom set pots. Cod tended to approach a pot along the seabed and were more likely to encounter the bottom set pot than the floated pot, whereas saithe more often approached in the water column. The capture efficiency was low for all species, but cod were more likely to be caught than saithe and haddock. Cod showed a high encounter rate, low entrance rate and high escape rate. For saithe, a low encounter rate was the chief factor limiting capture efficiency. The observed differences between cod and saithe were explained by species-specific food-search strategies. No difference in entrance rate, escape rate or catch efficiency between the two pot types were found.

Capture-based aquaculture (CBA) of Atlantic cod (Gadus morhua) has become increasingly important in recent years, and increased attention is being paid to animal welfare issues linked to these activities. Earlier studies showed that some cod develop secondary exophthalmia in captivity. This study investigated the development of secondary exophthalmia in two groups of wild-caught cod, one of which was exposed to rapid decompression causing acute barotrauma (treatment group) while the other was not (control group). Photographs and radiographs before and up to 33 days after barotrauma revealed a significant increase in overall eye protrusion caused by an accumulation of gas in the orbita in the treatment group, first observed on day 9 after decompression, while no protrusions were observed in the control group. Barotrauma was thus identified as an important trigger for the development of secondary uni- or bilateral exophthalmia of wild-caught cod. Two underlying mechanisms are suggested, where the more likely is residual swim bladder gas taking the route of least resistance, while the less likely is the exsolution of gas from the blood. Our results have implications for a wide range of contexts in which cod are rapidly brought to the surface from great depth.

In capture-based aquaculture (CBA) wild cod (Gadus morhua) are caught and held in sea cages in order to supply fresh, high-quality fish throughout the year. CBA of cod is attracting growing interest among the Norwegian fishing industry. The most common gear for CBA is the demersal seine net (Danish or Scottish seine). However, there are powerful incentives to increase the extent of CBA, but this will necessitate the participation of fishing vessels from the smaller coastal fleet that utilise commercial pot and longline gear. CBA legislation is fish-welfare oriented and stringent, and documentation of stress, injuries and survival of captured fish is required for new capture methods. Field experiments were performed in order to determine the condition at capture of cod caught by longline and pots, using a combination of behavioural, physical, physiological and reflex-based indicators. Mortality and recovery were recorded in an onboard holding tank. No dead cod were observed at capture and, except for hooking wounds, the fish appeared unharmed. There was a high prevalence of fish that were incapable of submerging (about 40%), which if not dealt with resulted in high mortality (proportion: 0.79; 95% CI: 0.62–0.89). The mortality of fish that were capable of submerging was lower in pot-caught (0.09; 95% CI: 0.04–0.21) than longline-caught (0.39; 95% CI: 0.24–0.58) cod. Physiological and reflex stress measurements indicated that pot-caught cod suffered less stress from capture and handling, which suggests that pots are preferable as CBA gear. However, our knowledge of temporal and spatial variation in the suitability of fish for live storage (e.g. buoyancy status) is currently insufficient to predict the CBA potential of pots and longline outside of experimental conditions. Reflex impairment could predict mortality for pot and longline gears, and the inclusion of buoyancy status as part of a reflex/buoyancy impairment (RBI) score greatly improved model predictability. However, there was evidence that the relationship between RBI and mortality was influenced by the suite of stressors experienced by the fish, and this must be taken into careful consideration when comparing this relationship between fisheries.

The aim of this study was to evaluate the effects of pumping height and repeated pumping on the generalized stress response and gross injuries in harvest sized Atlantic salmon. Fish pumped from a net pen at either high (5.2 m) or low (3.6 m) pumping heights showed an elevated, but not severe physiological stress response (pH, pCO2, lactate, potassium, haematocrit, and sodium) compared to fish netted (not pumped), while effects of different pumping heights were overall not demonstrated. Repeated pumping (either 3 or 6 times) also caused an increase in stress response (pH, pCO2, pO2, lactate, potassium and sodium) compared to control fish, and a positive dose-response relationship was found for lactate. No fish died as a result of pumping, nor were injuries observed that could exclusively be attributed to pumping. In conclusion, although elevated from the control groups, the stress response following increasing pumping height and repeated pumping as conducted in these experiments were not indicative of causing severe stress or injuries.

The aim of this behavioural study was to identify potential feeding attractants to be incorporated in an alternative longline bait for Atlantic cod. The attractants should be based on low-cost surplus resources that are not used for human consumption. The food search and feeding responses of wild caught cod to eight attractants made from products from the fishing and aquaculture industry were compared to traditional squid bait in a laboratory study. All attractants tested triggered feeding responses in cod, indicating that there are several by-products from the fishing industry that have potential as an attractant for an artificial longline bait. The three most effective attractants were herring processing by-products, sand eel hydrolysate and hydrolysate by-products from the shrimp industry, which all elicited stronger food search and feeding responses than squid. Our results indicate that both free amino acids and other unidentified compounds are important in eliciting feeding responses in cod. Thus, attempts to identify efficient feeding attractants to be incorporated in alternative baits should be based on using complete aqueous extracts, rather than isolating a mixture of potent components.

Most fishes and crustaceans respond to light, and artificial light sources may therefore be an efficient stimulus to manipulate behaviours in aquatic animals. It has been hypothesised that the catch efficiency of pots could be increased if prey, for example krill, can be attracted into the pots providing a visual stimulus and a source of live bait. To find which light characteristics are most attractive to krill, we tested the effects of light intensity and wavelength composition on Northern krill's (Meganyctiphanes norvegica) behavioural response to an artificial light source. The most attractive individual wavelength was 530 nm (green light), while broadband (425-750 nm) white light was an equally attractive light source. The intensity of the emitted light did not appear to have a direct effect on attraction to the light source, however it did significantly increase swimming activity among the observed krill. The most promising light stimuli for krill were tested to determine whether they would have a repulsive or attractive effect on cod (Gadus morhua); These light stimuli appeared to have a slightly repulsive, but non-significant, effect on cod. However, we suggest that a swarm of krill attracted to an artificial light source may produce a more effective visual stimulus to foraging cod.

Swimbladder puncture occurs frequently during fishing operations employed in capture-based aquaculture (CBA). The function, survival and welfare of cod Gadus morhua following controlled swimbladder puncture in the laboratory was investigated. Anaesthetised cod (n=30) were exposed to reduced pressure using a vacuum chamber and their swimbladders were punctured. The pressure reduction before puncture (~70%), location of the swimbladder puncture sites near the pin bones, intraperitoneal gas evacuation path leading to the anal area and rapid repair mechanism, among other puncture characteristics, were consistent with previous findings. The mortality was low (~6%) during the procedure and did not differ from that of the control group. The experimentally punctured cod were challenged by swimbladder reinflation in a flow-through pressure chamber supplied with a surveillance camera and remote pressure regulation. The punctured fish were capable of swimbladder inflation shortly after puncture and their bu...

Large numbers of wild members of commercially important fish species tend to congregate around fish farms. This effect is in conflict with the interests of fishermen because wild fish cannot be harvested close to fish farms due to the fishery exclusion zone, which is intended to prevent fishing gear from damaging the cages. We studied the potential for harvesting wild fish around a Norwegian salmon farm using three different types of pots. Our video observations showed that large quantities of wild fish, in particular saithe ( Pollachius virens ), aggregated in close vicinity of the cages. Pots set underneath salmon cages produced 17 times higher catches of saithe and five times higher catches of cod ( Gadus morhua ) than pots set at a distance of 100 m from the cages. The pots set underneath cages also caught larger cod. Large rigid pots were shown to be more efficient than smaller flexible pots. The stomach content of small cod was dominated by pellets, while large cod were feeding mainly on saithe. We suggest that dense aggregations of saithe and small cod beneath fish cages were associated with the supply of waste feed, whereas larger cod were attracted by the saithe. We conclude that pots have great potential for harvesting gadoids beneath salmon cages, but catches decline dramatically with the distance from cages.

During rapid decompression in the course of fish capture, cod (Gadus morhua L.) is unable to reabsorb excess gas in the swimbladder sufficiently rapidly, and the bladder ruptures as the gas expands. In capture-based aquaculture (CBA), knowledge of the severity of the rupture stress is required. The objective of this study was to describe the swimbladder rupture and healing processes. Cod captured by Danish seine at depths of between 130 and 200 m were stored in a netpen. At 0, 24, 72 and 384 h post-capture, randomly selected fish (n = 20) were dissected. All fish had ruptured the swimbladder, most close to the dorsal point of pinbones; these holes were sealed and the bladders were inflated. On testing, all the bladders withstood a minimum of 20 mmHg above atmospheric pressure, a strength that increased with time and inversely with the size of holes. As the overinflated bladder deflates after rupture, the two layers of the bladder wall slide relative to each other, closing the open gas passage in ...

Today bycatch of red king crab ( Paralithodes camtschaticus ) in stationary fishing gears targeting cod ( Gadus morhua ) is a severe problem in the Barents Sea, causing extra work for fishermen and damaging their gear and catches. Attempts to use bottom-set pots as an alternative to gillnets and longlines have been unsuccessful, as pots too are affected by large bycatches of crab. In this field study, pots were floated off the bottom in order to avoid crab bycatch. A standard two-chamber groundfish pot was modified by mounting a suspension arrangement that allowed the pot to orient itself with the current about 70 cm above the seabed. Fishing trials were conducted in the Varangerfjord (northern Norway) to compare floated and bottom-set reference pots. Floating the pots off the bottom eliminated king crab catches, while bottom-set pots caught an average of 21 crabs each. Moreover, floated pots caught significantly more cod than bottom-set pots (3.6 and 2.5 cod per pot, respectively), with the majority of the 45% increase being cod below minimum legal size. The catch increase was explained by the fact that the entrance of floated pots always maintained a down-current orientation, whereas in bottom-set pots shifting current directions may lead the odour plume away from the entrance, thereby reducing the rate of entry of cod. Full-scale fishing trials are needed in order to evaluate whether floated pots could become a commercially viable method of catching cod.

Atlantic cod (Gadus morhua) caught in recreational fisheries are commonly released, often with barotrauma after rapid decompression. Mouth-hooked, non-bleeding cod kept in a floating net pen showed mortalities ≥40% when angled from >50 m depth, likely because of cumulative stress from ongoing barotrauma and exposure to warm surface water. In a natural setting, however, cod have the opportunity to descend after release and are not restricted to the surface. In a follow-up study, 97.8% of similarly selected cod managed to dive following immediate release, whereas 2.2% were floaters. No mortality was observed for divers kept in cages, which were lowered to capture depth for 72 h. While the floaters would likely have died in a natural setting, no mortality was observed when they were recompressed and kept at capture depth for 72 h. The occurrence of swim bladder ruptures, swollen coelomic cavities, venous gas embolisms, and gas release around the anus was significantly influenced by capture depth (range 0–90 m). A supplementary radiology study showed inflated swim bladders in 87% of the cod after 72 h, and most barotrauma signs had disappeared after 1 month. This study encourages investigation of survival potential for physoclistous species when high mortalities are assumed but undocumented. Matching natural post-release and containment environment is essential in the experimental setup, as failure to do so may bias survival estimates, particularly when a thermocline is present. Assuming minimal predation, short-term mortality of cod experiencing barotrauma is negligible if cod submerge quickly by themselves and are otherwise not substantially injured. Survival of floaters may be increased by forced recompression to capture depth. Sublethal and long-term impacts of barotrauma remain to be studied. To ensure that cod have sufficient energy to submerge, anglers are encouraged to avoid fighting the fish to exhaustion and to minimize handling before release.

Three complementary seabed characterization tools with different spatial resolution were used to locate a research site and to assess physical effects of experimental otter trawling in the Barents Sea: an acoustic seabed classification system (RoxAnn), sidescan sonar and a video-sledge. The marine protected area (MPA) around Bear Island was chosen as it offered unfished reference sites. The area was topographically complex which resulted in certain challenges for choice of the experimental site due to the requirements of representativity and homogeneity and suitable sampling substrate. Systematic waylines with RoxAnn gave broad-scale patterns of bottom conditions, the more informative sidescan revealed topographic reliefs, whilst detailed information on sediment composition and small-scale seabed features was provided by the video-sledge. Accurate positioning of towed gears (trawl, sidescan and video-sledge) ensured unbiased data acquisition. Trawl doors and rockhopper gear created furrows that were visible by sidescan sonar and video. Intensive trawling also caused changes in the acoustic properties by increasing roughness and decreasing hardness. Results are consistent with a possible resuspension of the sediment and a homogenizing effect from the trawl doors and ground gear ploughing the area. The suitability and advantages of using spatially overlapping tools in trawl impact studies are discussed.

Fishing gear may continue to fish after it has been lost. Large catches have been observed during cruises to retrieve lost gillnets in Norwegian waters, especially in the fishery for Greenland halibut (Reinhardtius hippoglossoides). The Norwegian Greenland halibut is overexploited, and there is serious concern about the effect of lost nets on this stock. Catches in deliberately lost gillnets were studied in the fishery for Greenland halibut off the coast of mid-Norway in July 2000 and June 2001. Gillnet fleets were deployed at depths of between 537 and 851 m, and the soak time ranged from 1 to 68 days. Most of the catch consisted of the target species, and the proportions of different species did not change with soak time. All individuals caught were categorized in terms of seven condition states. A gradual shift from fresh to decomposed individuals over time was evident. The catching efficiency of gillnets decreased with soak time, presumably due to the weight of the catch causing the headline height to decrease, and after 45 days was only about 20–30% of that of nets used in the commercial fishery. Catch rates were estimated after stabilization at 67–100 and 28–43 kg per day per gillnet fleet in 2000 and 2001, respectively. The results indicated that gillnets lost in this area continue to fish for long periods of time. Annual losses of nets need to be quantified in order to estimate the effects of ghost fishing on stock levels, a figure that is currently lacking.

Use of decommissioned North Sea oil platforms as artificial reefs may provide an alternative to their being removed. Three fishing experiments with gillnet fleets lasting 3–5 days and using different mesh sizes were conducted in the vicinity of two platforms to study their potential as sites for commercial fishing. In each case, five fleets were set in a star-shaped pattern centred around the platform and running up to a distance 1400 m. Catches consisted mainly of cod (Gadus morhua) and saithe (Pollachius virens), and in one case also of ling (Molva molva). In two experiments, catch rates of nets set within a distance of 110–165 m of the platform were three to four times higher than those of nets set at greater distances. In the third experiment, the highest catches were taken 150–300 m from the platform, also by a factor of four compared to catches taken at greater distances. However, patterns differed among species, areas, and seasons. Catch rates varied considerably between fishing days, and in only one experiment did catch rates (specifically of ling) decline consistently throughout the fishing period, suggesting gradual depletion. Although the study provided evidence of pronounced aggregations of fish close to the platforms, responses are complex and results are inconclusive regarding species-specific temporal and spatial patterns.

Better knowledge of food search behavior in fish is essential for studies that aim to improve longline fishing, particularly through bait development. This review provides an overview of our understanding of how fish detect and locate sources of food odour, focusing on the stimuli and sensory modalities involved, and on factors that affect feeding activity. Studies that identify feeding attractants and efforts to develop alternative longline baits are presented. The review reveals that such studies are few in number, and that to date there are no alternatives to traditional baits in commercial longlining despite the growing demand for these resources, which are also used for human consumption. The chemical compounds that elicit food search behavior differ from species to species, and species selectivity could be improved by incorporating specific feeding attractants in manufactured baits. The unique properties of chemical stimuli and odour dispersal form the basis for improving longline efficiency through the development of a long-lasting bait. Vision is important in prey capture, and manufactured baits can be made more visible than natural baits by increasing the contrast (e.g. via fluorescent or polarising coatings) and creating motion through buoyancy. Physical properties such as size, shape, texture and strength can also be manipulated in a manufactured bait to improve catch efficiency. Knowledge obtained from studies of various aspects of food search behaviour is of paramount importance for future research aimed at alternative bait development and improving longline fishing. publishedVersion

Bottom trawling activities resuspend large amounts of sediment and may be the main agent of sediment transportation in some areas. During periods of intensive fishing by large trawler fleets the high-turbidity environmental conditions they create may become semi-permanent. Little is known about the potential effects of this resuspended sediment on the survival and physiology of marine fish. We carried out a worst-case-scenario simulation whereby groups of cod Gadus morhua were exposed to the highest reported mud concentration behind trawls (550 mg l -1 ) for periods of 24 h, 5 d and 10 d. No mortality was observed in any of the experimental groups. Histological analy- ses of gill lamellae of fish exposed to mud suspension for 24 h showed acute pathological changes in the form of multifocal degenerative lesions. After 5 d exposure, adaptive changes to cope with the turbid environment were observed. These comprised hypertrophy and hyperplasia of the gill epithe- lium and became more marked and widespread after 10 d exposure. The gill lesions observed were similar to those reported in other species exposed to a turbid environment and were in those cases reversible. Analyses of blood plasma cortisol levels showed higher values for fish in the 5 d exposure group than for fish in the 1 d exposure group. No other between-group differences were significant. The within-group variation was high in all groups but especially in the 10 d exposure group.