Large Cod Research Articles

COD and CSD based model for in-plane stiffness of symmetric laminates with cracks in plies and local delaminations: Analysis of crack face sliding

In-plane thermo-elastic constants of symmetric damaged laminates containing transverse cracks in plies and local delaminations starting from crack tip are predicted using a crack opening (COD) and crack sliding displacement (CSD) based approach. An exact elastic analysis shows that the displacement gap on the delamination crack surfaces does not enter the stiffness expressions explicitly. The delamination affects the stiffness via larger COD and CSD of the intralaminar crack. This means that the same expressions for cracked laminates with and without delaminations can be used but with different expressions for COD and CSD. Finite element method is used to analyze the CSD dependence on delamination length and crack density. The obtained approximative expressions for CSD are in a good agreement with FEM. It is shown that in cases when it depends on CSD only, the predicted shear modulus of laminates is in an excellent agreement with direct FEM calculations. The used homogenization over couples of off-axis plies (monoclinic materials) in CSD expressions for balanced laminates is validated.

Change points in marine recreational fisheries – The impact of stock status and fisheries regulations: A case from the western Baltic Sea

Marine recreational fisheries can be viewed as social-ecological systems in which sudden biological changes can affect interconnected social components. The Baltic Sea underwent various regime shifts, and the stock of western Baltic cod (Gadus morhua), a commercially and recreationally important target species, collapsed in 2016/17. This resulted in the first-time introduction of a bag limit in the recreational cod fishery. An eleven-year time series of recreational fisheries data was used to identify change points in the number of German cod anglers and in their catch and harvest rates, which may have occurred corresponding to the stock collapse. The number of anglers as well as their catch and harvest rates showed pronounced intra- and inter-annual fluctuations and the share of large cod in the catch decreased. Nonetheless, catch rates corresponded only weakly with cod stock biomass, suggesting that this fishery-related indicator was more responsive to the introduction of the bag limit than to the stock status. The study underlines the importance of long-term monitoring programs at appropriate spatial and temporal scales as a prerequisite for identifying change points in recreational fisheries and as an integral component of fisheries management to improve management in the future.

Effects of large salinity fluctuations on an anaerobic membrane bioreactor treating phenolic wastewater

High salinity is becoming more common in industrial process water and final effluents, particularly when striving to close water loops. There is limited knowledge on the anaerobic treatment of chemical wastewaters characterized by distinct salinity fluctuations. This study investigates the high and fluctuating salinity effects on the conversion capacity and membrane filtration performance of an anaerobic membrane bioreactor (AnMBR) in treating phenol-containing wastewater. The AnMBR operated for 180 days with sodium concentrations between 8 and 37 gNa+.L−1. At ≤ 26 gNa+.L−1, approximately 99% COD and phenol removal efficiencies were achieved. At 37 gNa+.L−1, phenol and COD removal efficiencies decreased to 86 and 82%, respectively, while the biomass specific methanogenic activity was 0.12 ± 0.05 gCOD-CH4.gVSS−1.d−1. Due to large salinity fluctuations, phenol and COD removal efficiencies reduced to ≤ 45% but recovered to ≥ 88%. Compared to phenol conversion, methanogenesis was more severely affected. Calculations showed a maximum in-situ phenol conversion rate of 25.5 mgPh.gVSS−1.d−1. Concomitantly, biomass integrity was compromised, and the median particle size severely dropped from 65.6 to 4.3 μm, resulting in a transmembrane pressure increase above 400 mbar. Cake layer resistance to filtration contributed to 85% of the total resistance. Nonetheless, all biomass was effectively retained in the AnMBR. A change in salinity ≥ 14 gNa+.L−1 substantially reduced the microbial richness and diversity. The microbial community was dominated by Bacteria belonging to Clostridiales and Archaea of the orders Methanosarcinales and Methanobacteriales. Our findings demonstrate AnMBRs as suitable techniques for treating chemical process water, with possible subsequent reclamation, characterized by high phenols concentrations and largely fluctuating salinity levels.

Enhancement of organic household waste anaerobic digestion performances in a thermophilic pilot digester

Performances of organic household waste anaerobic digestion was investigated in a new horizontal thermophilic pilot digester of 50 L total capacity. The operation was performed under favorable conditions without any chemical additives. The presence of predigested cattle manure in the digester provided an interesting buffer capacity that was able to balance the produced fatty acids during the digestion process.The biomethane production reached 0.44 m3 CH4/Kg VS while achieving a COD removal of 70%.The operating time and the anaerobic digestion steps were shortened under thermophilic wet digestion. Only 4 days were sufficient to reach the daily maximum methane production (0.084 m3 CH4/(kgVS.day)) and 10 days to reach 80% of the overall biomethane potential. The process efficiency in removing volatile solid was found to be more than 35% within 5 days.Therefore, wet anaerobic digestion under thermophilic temperature is suitable for industrial scale anaerobic digestion of biowaste regarding the high biomethane yield, the large COD and solid removing and the shortness of process operating time.

Zoned strategy for water pollutant emissions of China based on spatial heterogeneity analysis.

A zoned strategy based on the spatial heterogeneity of water pollutant emissions is helpful for water environment management. With principal component analysis and clustering analysis, 31 provincial administrative regions (not including Hong Kong, Macao, and Taiwan regions) of China with emissions of 12 kinds of water quality indicators had been categorized into 4 zone type regions. Zone type-1 is the largest emissions of heavy metals, including mining-developed provinces of Hunan and Jiangxi. Zone type-2 is constituted of economically and agriculturally developed with large COD, NH4+-N, TP, and TN emissions, including Hebei, Jiangsu and Zhejiang, Anhui, Shandong, Henan, Hubei, Guangdong, and Sichuan. Zone type-3 only contains Shanxi with massive oil and volatile phenol emissions. Zone type-4 is the other 19 provinces with small discharges of water pollutants. Zone type-4 could be divided into three subclasses which are related to the location of these areas. With these cluster zones, the targeted water pollutant emissions strategy has been put forward in the paper. These methods and ideas of this paper can be further applied to the analysis of spatial and temporal differentiation of pollutant discharges in basins. With the zoning regions, more concrete water pollution prevention and control strategies can be set at a national level.

Volatile fatty acid production from saline cooked mussel processing wastewater at low pH

The production of VFA using as substrate the wastewater produced in a cooked mussel processing factory, containing large COD (13.7 ± 3.2 g COD/L), salt concentrations (21.8 ± 2.8 g NaCl/L) and characterized by low pH (4.6 ± 0.6) was evaluated. This wastewater was fed to a 5-L completely stirred tank reactor operated in continuous mode. The conversion efficiency of its COD content into volatile fatty acids (VFA) was evaluated. The maximum acidification of 43% (total VFA on soluble COD basis) was obtained when an organic loading rate of 2.5 ± 0.4 g COD/(L·d) was applied to the reactor and corresponded to a VFA volumetric productivity of 0.72 ± 0.07 g CODVFA/(L·d). Under steady-state conditions, the obtained mixture of VFA was composed by 80:18:2 as acetic:propionic:butyric acids (percentage of VFA on soluble COD basis). Carbohydrates were degraded up to 96% while protein fermentation did not take place, probably due to the low pH value, limiting the maximum acidification of the wastewater. Batch experiments showed that the increase of the pH from 4.2 to 4.9 by the addition of NaHCO3 resulted in the improvement of the acidification and changed the VFA mixture composition. Thus, this study demonstrates the opportunity of using complex substrates, as cooked mussel processing wastewater, to produce rich-VFA streams under unfavourable operational conditions, such as high salinity and low pH.

Long-term changes in spatial overlap betweeninteracting cod and flounder in the Baltic Sea

The strength of interspecific competition and predator–prey interactionsdepends on the area of co-occurrence of the interacting species. Therefore, it isnecessary to quantify the changes in the spatial overlap of trophically connectedspecies to understand the outcomes of species interactions. In the Baltic Sea, theinterplay between cod and flounder has previously been neglected. In this study, we usefour decades of data on cod and flounder distributions covering the southern and centralBaltic Sea to: (1) model and map the changes in the distributions of the two speciesusing generalized additive models; (2) quantify the temporal changes in the potentialcompetitive and predator–prey interactions between them using spatial overlap indices;(3) relate these changes in overlap to the known dynamics of the different cod andflounder populations in the Baltic Sea. Competition overlap has continuously increasedfor cod, from the beginning of the time-series. This is a possible cause of the observeddecline in feeding levels and body condition of small and intermediate sized cod.Flounder overlap with large cod instead has decreased substantially, suggesting apredation release of flounder, potentially triggering its increase in abundance anddistribution range observed in the last decades.

High methanogenic activity of a three-stage UASB in relation to the granular sludge formation

A new UASB (upflow anaerobic sludge blanket) system with three-stage concept and granular sludge formation was developed to provide a very high process activity, in terms of a high energy yield and a large optimum COD loading rate, from ethanol wastewater at 37 °C and a controlled pH of 5.5 in the first bioreactor with recirculation of the final overflow from the third to the first two bioreactors to lower the amount of sodium hydroxide used for pH control in the first bioreactor and to increase the total alkalinity of the whole system. The proper volumetric ratio of the three-stage UASB with flocculant sludge provided the dominance of the three sequencial steps of acidogenesis, acetognesis and methanogenesis to occur in the respective bioreactors, causing a higher process performance and giving the optimum COD loading rate of 15 kg/m3d. The presence of granular sludge in all three bioreactors, resulted from the slow increment in the COD loading rate over a long operation period with high levels of microbial concentrations in all three bioreactors under the continuous feed operation and steady sate condition. This further increased the optimum COD loading rate from 15 to 25 kg/m3d (calculated from the total liquid volume) with an extremely high energy yield of 11,740 kJ/kg COD applied.

Synergism between cruising cod and ambush sculpin predators on 0-group gadoids is modified by daylight cycle and presence of aggressive wolffish

Shorthorn sculpin (Myoxocephalus scorpius) and large cod (300–400 g body weight) are important predators on newly settled 0-group cod (Gadus morhua) and saithe (Pollachius virens) in Porsangerfjorden in northern Norway. The Atlantic wolffish (Anarhichas lupus) used to be abundant but is now very rare in the fjord. Video recorded experiments showed that interactions between shorthorn sculpins, wolffish and large cod affected predation rates on small 0-group cod and saithe in tanks with a gravel, cobble and seaweed (Fucus serratus) substrate. We found that sculpins were unable to catch 0-group specimens when they were the only predatory species in the experimental tank and the lights were left on 24 h a day (to simulate the midnight sun), and that they did not even attempt to catch them. The addition of a large cod to the tank increased sculpin attack rates and predation success significantly.The “cod effect” was due to 0-group specimens avoiding attacks by escaping into the cobbles or vegetation, were they could be more easily reached by the sculpins. When tanks were supplemented with a wolffish in addition to the cod, both sculpin and cod predation success was lowered by approximately 50% in the 24-h light regime. When the experimental setup was changed to a day/night light cycle, however, the wolffish presence had no effect. Also, sculpins in tanks without cod and wolffish went from consuming zero to 29% of the 0-group specimens in the tank when the light regime went from 24-h light to day/night. Sculpins and cod were most effective predators on 0-group cod and saithe at dusk/night/dawn, and the presence of a cruising predator like cod increased sculpin predation success and probably vice versa.The experimental data indicate that rebuilding wolffish stocks in the fjord system may make the bottom substrate more protective for 0-group specimens of cod and saithe, by limiting the foraging volume of an effective bottom-dwelling 0-group predator like the sculpin. Further field and lab studies must be conducted before the reported findings optionally can be turned into a management advice.

Extrapolating predation mortalities back in time: an example from North-east Arctic cod cannibalism

ABSTRACTCannibalism is known to be a significant source of natural mortality of young North-east Arctic (NEA) cod. Cannibalism data, starting from 1984, have been used in NEA cod stock assessments since 1995, which has led to inconsistency in the cod abundance time series from 1946 to the present. To address this inconsistency, this study estimates the cannibalism-induced mortality (M2) of NEA cod at age 3–5 for the period 1946–1983. Combined qualitative and quantitative cod stomach content data for 1984–2010 were used to make the M2 estimations for age groups 3–5 (ICES 2014), then different factors including SSB were used to examine which covariates explained variability in M2 and thus make predictions for 1946–1983. The level of cannibalism was estimated to be high in the 1950s – early1960s. VPA-based assessment was run using these estimated M2 values. As a result, numbers of cod eaten by their conspecifics in the historical period and new increased recruitment estimates at age 3 were computed. The main factors affecting cannibalism appeared to be young cod abundance, total stock biomass (TSB) of large cod, and capelin total stock biomass (which represents an alternative prey). The problems involved in using the new recruitment time series in fishery management are discussed. The methodology presented here represents a generic approach to extending predation mortalities back in time to improve historical stock estimates.

The end of the world, or just ‘goodbye to all that’? Contextualising the red deer heap from Links of Noltland, Westray, within late 3rd-millennium cal BC Orkney

As part of a major international research project, The Times of Their Lives, a programme of radiocarbon dating and Bayesian modelling was undertaken to refine the chronology of activities in one small but important part of the extensive Late Neolithic and Bronze Age settlement on Links of Noltland on the island of Westray, Orkney. The selected area (Trench D) is well known for having produced, next to a wall, the remains of a heap of at least 15 red deer carcasses, on top of which had been placed a large cod, a gannet’s wing along with part of a greater black-backed gull, and a pair of large antlers. This remarkable deposit had been preceded by, and was followed by, periods of cultivation and the deposition of domestic refuse. Refined date estimates have been produced, based on 18 radiocarbon determinations obtained from 16 samples from Trench D (including nine newly obtained dates, three from individual deer in the heap). These clarify when, during this long sequence of activities, the deer were heaped up: probably in the 22nd century cal BC, around the same time as Beaker pottery was deposited elsewhere on the Links. This allows comparison between the dated activities in this part of the site with activity elsewhere on the Links and also with other episodes of deer deposition in 3rd-millennium cal BC Orkney. It encourages exploration of the possible reasons for what appears to be a remarkable act of structured deposition. The significance of an earlier, much larger scale deposit featuring cattle remains at Ness of Brodgar is discussed in exploring the nature of Orcadian society and practices during the second half of the 3rd millennium cal BC.

Diet of endangered Steller sea lions (Eumetopias jubatus) in the Aleutian Islands: new insights from DNA detections and bioenergetic reconstructions

The endangered western stock of Steller sea lion (Eumetopias jubatus (Schreber, 1776)) still declines in the western Aleutian Islands and accurate diet information is vital to test leading hypotheses. We undertook the first bioenergetic diet reconstruction using both molecular and hard part prey identifications from >600 scats collected in March–April 2008 and 2012. Atka mackerel (Pleurogrammus monopterygius (Pallas, 1810)) remained a primary prey (17%–27% by energy), but large (mean 60 cm) Pacific cod (Gadus macrocephalus Tilesius, 1810) also emerged as important prey (20%–24%) in a more diverse diet than previously reported, with Cottidae and smooth lumpsucker (Aptocyclus ventricosus (Pallas, 1769)) also contributing ∼10%. DNA detections highlighted a potentially important and previously underestimated prey, giant Pacific octopus (Enteroctopus dofleini (Wülker, 1910) (diet contribution 2%–15%, dependent on prey size assumptions). Although 504 unique DNA identifications resulted in significant increases for cephalopods, Pacific cod, and smooth lumpsucker, hard part alone species rankings were similar to composite ones and bioenergetic species rankings similar to occurrence-based ones. Retention or regurgitation of large cephalopod beaks, the removal of large cod heads, and skeletal fragility of lumpsuckers may explain these differences. DNA identifications provide valuable comparative and complementary prey occurrence data for pinnipeds, but composite diet estimates are optimal.

Correlations of age and growth rate with microbiota composition in Atlantic cod (Gadus morhua) larvae

Little information is available on the link between host development (growth rate and ontogeny) and the composition of the microbiota in fish larvae. This study was carried out to examine potential correlations of microbiota composition with age and growth rate of Atlantic cod larvae. Small and large cod larvae of the same age, representing slow and fast growing individuals, were sampled 10 times during a period of 42 days post hatching (dph), and the composition of the larval microbiota was investigated using a PCR/DGGE (Denaturing Gradient Gel Electrophoresis) strategy. We found significant differences in the intestinal microbiota of small and large larvae of the same age for 4 of the 10 age stages studied. We further found that the variation in the composition of the larval microbiota was more strongly correlated to age than to growth rate for larvae up to 28 dph, whereas for the older larvae growth rate and age was equally correlated to the composition of the microbiota. These results indicate that larval development may structure the microbiota through a change in selection pressure due to host-microbe and microbe-microbe interactions, and that the composition of the microbiota may influence larval development through improved energy gain.

Diet of Norwegian coastal cod (Gadus morhua) studied by using citizen science

Abstract The Norwegian coastal cod ( Gadus morhua ) is a keystone species in the food web of northern Norwegian fjords. Their relatively stationary populations might specifically depend on local food resources, but the diet of cod has rarely been studied in fjord systems. Using a citizen science approach, where recreational anglers and tourists participated in the sampling, we studied small-scale differences in the diet composition of cod in a fjord system in northern Norway. We compared the cod diet from the MPA Saltstraumen, characterised by strong tidal currents and a highly diverse and abundant fauna, with the inner fjord area of Skjerstadfjord. The diet composition of cod significantly differed between both areas within the fjord. Although fish was the dominant prey in both areas, cod consumed > 40% invertebrates in terms of weight, even in the cod size class of 70–99 cm. The invertebrate prey also caused the observed spatial differences. In Saltstraumen, brittle stars (Ophiuroidea), crabs (Brachyura) and sea cucumbers (Holothuroidea) were important food sources for cod, while sea urchins (Echinoidea), clams (Bivalvia), shrimps (Caridea) and krill (Euphausiacea) dominated the diet in the inner Skjerstadfjord. The high densities of sessile fauna in the dynamic environment of Saltstraumen, was only partly reflected in the diet of cod, with only Holothuroidea found in 17% of the stomachs. High rates of empty stomachs (24%), cannibalism as well as a higher proportion of low-energy prey in the diet of large cod, may indicate a shortage of high quality food in Skjerstadfjord. The samples for this study were collected through a citizen science campaign. This approach might provide opportunities to be used for coastal ecological monitoring with potential applications in local ecosystem management strategies through public involvement.

Cod Heads, Stockfish, and Dried Spurdog: Unexpected Commodities in Nya Lödöse (1473–1624), Sweden

During medieval and early modern times, fish products were intensively traded over long distances. Fish was an important part of the diet, and there was a wide range of fresh as well as preserved fish for the consumers to choose among. In this article the fish bone assemblage from the town Nya Lodose (1473–1624), Sweden, is used to explore what kind of fish were available for the inhabitants to buy. Marine fish was generally preferred over freshwater species, and while the deep sea fishing most probably was highly professionalized, fishing in lakes and rivers must have been rare. Most importantly, the article reviews the evidence for different kinds of fish commodities identified in the assemblage from Nya Lodose. Except from stockfish and herring, dried heads from large cod and ling, as well as dried pike, flatfish, and spurdog were also identified.

Shifts in spawning phenology of cod linked to rising sea temperatures

AbstractWarming temperatures caused by climate change have the potential to impact spawning phenology of temperate marine fish as some species have temperature-dependent gonadal development. Inter-annual variation in the timing of Atlantic cod (Gadus morhua) spawning in the northern North Sea, central North Sea and Irish Sea was estimated by calculating an annual peak roe month (PRM) from records of roe landings spanning the last three decades. A trend towards earlier PRM was found in all three regions, with estimates of shifts in PRM ranging from 0.9 to 2.4 weeks per decade. Temperatures experienced by cod during early vitellogenesis correlated negatively with PRM, suggesting that rising sea temperatures have contributed to a shift in spawning phenology. A concurrent reduction in the mean size of spawning females excluded the possibility that earlier spawning was due to a shift in size structure towards larger individuals, as large cod spawn earlier than smaller-sized individuals in the North Sea. Further research into the effects of climate change on the phenology of different trophic levels within the North Sea ecosystem should be undertaken to determine whether climate change-induced shifts in spawning phenology will result in a temporal mismatch between cod larvae and their planktonic prey.

Floated cod pots with one entrance reduce probability of escape and increase catch rates compared with pots with two entrances

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 (≥44cm) 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.

Host size-dependent anisakid infection in Baltic cod Gadus morhua associated with differential food preferences.

A significant increase in the infection level of Baltic cod Gadus morhua with the anisakid nematode larvae Contracaecum osculatum and Pseudoterranova decipiens has been recorded during recent years due to the expanding local population of grey seals Halichoerus grypus, which act as final hosts for these parasites. Here, we report from an investigation of 368 cod (total length [TL] 6-49 cm; caught in ICES Subdivision 25) that the infection level of juvenile cod (TL 6-30 cm) with larvae of C. osculatum and P. decipiens is absent or very low, whereas it increases drastically in larger cod (TL 31-48 cm). A third nematode Hysterothylacium aduncum was rarely found. The study indicates that the prey animals for large cod act as transport hosts for the parasite larvae. Analyses of stomach contents of cod caught in the same area (2007-2014) showed that small benthic organisms (including polychaetes Harmothoë sarsi) are preferred food items by small cod, the isopod Saduria entomon is taken by all size classes, and sprat Sprattus sprattus are common prey items for cod larger than 30 cm. Parasitological investigations (microscopic and molecular analyses) of H. sarsi (100 specimens) and S. entomon (40 specimens) did not reveal infection in these invertebrates, but 11.6% of sprat (265 specimens examined) was shown to be infected with 1-8 C. osculatum third stage larvae per fish. Analyses of sprat stomach contents confirmed that copepods and cladocerans are the main food items of sprat. These observations suggest that the C. osculatum life cycle in the Baltic Sea includes grey seals as final hosts, sprat as the first transport host and cod as second transport host. It may be speculated that sprat obtain infection by feeding on copepods and/or cladocerans, which could serve as the first intermediate hosts. One cannot exclude the possibility that the size-dependent C. osculatum infection of cod may contribute (indirectly or directly) to the differential mortality of larger cod (>38 cm) compared to smaller cod (<30 cm) recently recorded in the Baltic cod population.

Marine ecosystem connectivity mediated by migrant-resident interactions and the concomitant cross-system flux of lipids.

Accumulating research argues that migrants influence the functioning and productivity of local habitats and ecosystems along migration routes and potentially drive cross‐system energy fluxes of considerable magnitude, yet empirical documentation of local ecological effects and descriptions of the underlying mechanisms are surprisingly rare. In this study, we discovered migrant–resident interactions and substantial cross‐system lipid transportation in the transition zone between the Baltic Sea and the North Sea where a resident cod population (predators) was found to interact with a herring population (prey) on a seasonal basis. We traced the lipids, using fatty acid trophic markers (FATM), from the herring feeding grounds in the North Sea to the cod livers in the Western Baltic Sea. Time series analysis of population dynamics indicated that population‐level production of cod is positively affected by the herring subsidies. However, the underlying mechanisms were more complicated than anticipated. During the herring season, large cod received most of its dietary lipids from the herring, whereas smaller cod were prevented from accessing the lipid pool due to a mismatch in predator–prey size ratio. Furthermore, while the herring were extremely rich in bulk energy, they were surprisingly poor in a specific functional fatty acid. Hence, our study was the first to illustrate how the magnitude cross‐system fluxes of subsidies in migrant–resident systems are potentially constrained by the size structure of the resident predator population and the nutritional quality of the migrants.

Pulse trawl fishing: characteristics of the electrical stimulation and the effect on behaviour and injuries of Atlantic cod (Gadus morhua)

Abstract In the North Sea flatfish fishery, electric pulse trawls have been introduced to replace the conventional mechanical method. Pulse trawls reduce the fuel consumption, reduce adverse impact on the ecosystem but cause injuries in gadoids. We describe the design and electrical properties of pulse trawls currently in use and study the behavioural response and injuries in cod exposed to electrical pulses under controlled conditions. Pulse trawls operate at an average power of 0.7 kW m−1 beam length and a duty cycle of ∼2%. The electric field is heterogeneous with highest field strength occurring close to the conductors. Cod were exposed to three different pulse types for a range of field strengths, frequencies, and duty cycles. Two size classes were tested representing cod that escape through the meshes (11–17 cm) and market-sized cod that are retained in the net (34–56 cm). Cod exposed to a field strength of ≥37 V m−1 responded by moderate-to-strong muscular contractions. Some of the large cod (n = 260) developed haemorrhages and fractures in the spine, and haemal and neural arches in the tail part of the body. The probability of injuries increased with field strength and decreased when frequency was increased from 100 to 180 Hz. None of the small cod (n = 132) were injured and all survived. The field strength at the lateral boundaries of the trawl was too low to inflict injuries in cod.