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J. Rasmus Nielsen - One of the best experts on this subject based on the ideXlab platform.
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Opening of the Norway pout box: will it change the ecological impacts of the North Sea Norway pout fishery?
ICES Journal of Marine Science, 2018Co-Authors: Matthieu Bigné, J. Rasmus Nielsen, Francois BastardieAbstract:Abstract The small-mesh Norway pout (Trisopterus esmarkii) fishery intensified in the northern North Sea during the 1970s. Concerns about juvenile gadoid bycatch led to the “Norway pout box” closure along the Scottish coast in 1977. To assess the justification of the box today and the potential current impacts of opening the box, we evaluate the closure effects on selected fish stocks by analysing high-resolution research survey and commercial fishery data. The species- and size-specific distribution patterns in relation to environmental influencing factors are analysed for Norway pout and important bycatch species inside and outside the box. Relative distribution of benthic habitats is compared between inside–outside areas according to fish occurrence and fishery spatial footprint. No area differences in fish size composition are observed. However, species abundance depends significantly on habitat and depth whose area distribution is not homogenous. The current fishery is mainly in deeper, muddy seabeds. Haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus) density is higher in shallow and sandy habitats, with a relatively larger area coverage inside the box. If a box opening implies relatively more fishery in those habitats, then increased bycatch can be expected. Consequently, closure of certain benthic habitats may instead be better management, opening new fishing opportunities without risk.
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Influence of grid orientation and time of day on grid sorting in a small-meshed trawl fishery for Norway pout (Trisopterus esmarkii)
Aquatic Living Resources, 2012Co-Authors: Ole Ritzau Eigaard, Bent Herrmann, J. Rasmus NielsenAbstract:A lightweight sorting grid was developed to reduce bycatch in the Danish small-meshed trawl fishery (22 mm full mesh in the cod end) for Norway pout in the North Sea. Experimental fishing with the grid demonstrated the possibility to capture Norway pout with only a minimum of unintended bycatch. Fishing with two different grid orientations, backwards and forwards-leaning, in distinct day and night hauls, resulted in an estimated release of between 88.4 and 100% of the total number of haddock (Melanogrammus aeglefinus ) and whiting (Merlangius merlangus ) entering the trawl. However, bycatch reductions were not significantly different between day and night or between grid orientations, indicating that the grid rejection of haddock and whiting is not influenced by fish behaviour. The loss of the target species, Norway pout, was low (between 5.6% and 13.7%) in comparison with the bycatch excluded, and clearly length dependent. Consequently, loss of target species would vary with the size structure of the population fished. Although results were not statistically significant, length-based analyses indicated that the grid rejection likelihood for particularly smaller Norway pout (
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Do Norway pout (Trisopterus esmarkii) die from spawning stress? Mortality of Norway pout in relation to growth, sexual maturity, and density in the North Sea, Skagerrak, and Kattegat
ICES Journal of Marine Science, 2012Co-Authors: J. Rasmus Nielsen, Henrik Sparholt, Gwladys I. Lambert, Francois Bastardie, Morten VintherAbstract:Mortality of Norway pout in relation to growth, sexual maturity, and density in the North Sea, Skagerrak, and Kattegat J. Rasmus Nielsen1*, Gwladys Lambert1, Francois Bastardie1, Henrik Sparholt2, and Morten Vinther1 National Institute of Aquatic Resources (DTU-Aqua), Technical University of Denmark, Charlottenlund Castle, DK-2920 Charlottenlund, Denmark ICES, H. C. Andersens-Boulevard 44-46, DK-1553 Copenhagen V, Denmark *Corresponding author: tel: +45 35 88 33 81; fax: +45 35 88 33 33; e-mail: rn@aqua.dtu.dk
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Maturity and growth population dynamics of Norway pout (Trisopterus esmarkii) in the North Sea, Skagerrak, and Kattegat
ICES Journal of Marine Science, 2009Co-Authors: Gwladys I. Lambert, J. Rasmus Nielsen, Lena I. Larsen, Henrik SparholtAbstract:The population dynamics of the Norway pout stock in the North Sea are investigated by statistical analyses, and GIS of ICES International Bottom Trawl Surveys (IBTS) and Danish commercial catch data from 1983 to 2006. The stock spawns mainly around mid-February along the northeastern English and Scottish coasts and between Shetland and Norway. Sex ratios indicate that males, which mature younger than females (age-at-50%-maturity, respectively, 1.2 and 1.5 years), migrate out of the Skagerrak – Kattegat to the spawning grounds before females. There is a decrease in the 2+-group maturity ratios as well as in weight and female length from before to after spawning. The results indicate spawning mortality. Only some 20% of the 1-group reaches maturity in the first quarter, which is higher than assumed in the stock assessment. Although the maturity ogives are variable over time, this difference should be taken into account when estimating spawning-stock biomass in routine assessments. Growth is also variable, with a tendency for male maximum length to be smaller than that of females, and immature fish to be smaller than mature ones in each age group. The juvenile growth rate is higher when the stock density is low and results in a reduced age-at-50%-maturity. Besides these intraspecific patterns, the growth rates show interspecific links to stock sizes of the important predators: cod, haddock, and whiting.
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Non-predation natural mortality of Norway pout ( Trisopterus esmarkii ) in the North Sea
ICES Journal of Marine Science, 2002Co-Authors: Henrik Sparholt, Lena I. Larsen, J. Rasmus NielsenAbstract:Based on age disaggregated data on catch rates in bottom trawl surveys, commercial catches, and the number consumed by the North Sea piscivorous predators, new estimates of non-predation natural mortality, M1, are obtained for Norway pout [Trisopterus esmarkii (Nilsson)]. Simple log catch ratio analysis and rough maximum likelihood procedures are applied. The analysis focus on the year classes 1977-1981 and 1987-1991, which are represented in the extensive stomach sampling of North Sea piscivorous fish in 1981 and 1991. Although the M1 of Norway pout varied between the two periods, in both periods it increased with age and was very high for age 2 and older fish (0.10 for age 1, 1.74 for age 2, 2.58 for age 3 and 3.05 for age 4 for the 1977-1981 year classes and 0.10 for age 1, 2.03 for age 2, 3.04 for age 3 and 4.39 for age 4 for the 1987-1991 year classes). This difference between the two periods is not significant. Survey data from each quarter of the year show that the main mortality takes place between the 1st and the 2nd quarter of the year, i.e. from before to after spawning, thus pointing at spawning as the main factor.
Niels Jørgen Olesen - One of the best experts on this subject based on the ideXlab platform.
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Isolation of viral haemorrhagic septicaemia virus (VHSV) from wild marine fish species in the Baltic Sea, Kattegat, Skagerrak and the North Sea.
Virus Research, 1999Co-Authors: Helle Frank Mortensen, Ole Eske Heuer, Niels Lorenzen, Lars Otte, Niels Jørgen OlesenAbstract:In order to analyse the occurrence of viral haemorrhagic septicaemia virus (VHSV) in the marine environment surrounding Denmark, fish tissue samples were collected on four cruises with the research vessel H/S Dana in 1996 and 1997. The sampling comprised 923 samples totalling 7344 fish representing 29 different species. VHSV was isolated from 24 fish samples from the Baltic Sea, four samples from Skagerrak and three samples from the North Sea. The virus-positive host species included herring Clupea harengus (11 isolates), sprat Sprattus sprattus (eight isolates), cod Gadus morhua (six isolates), rockling Rhinonemus cimbrius (one isolate), Norway pout Trisopterus esmarkii (one isolate), blue whiting Micromesistius poutassou (one isolate), whiting Merlangius merlangus (two isolates) and lesser argentine Argentina sphyraena (one isolate). VHSV has previously been reported from cod and herring, but not from the other five species. A virus belonging to serogroup II of the aquatic birnaviruses was isolated from three samples of flounder Platichthys flesus and three samples of dab Limanda limanda and a virus preliminary identified as iridovirus (lymphocystis virus) was isolated from seven samples of long rough dab Hippoglossoides platessoides.
Nicola Bain - One of the best experts on this subject based on the ideXlab platform.
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a survey of wild marine fish identifies a potential origin of an outbreak of viral haemorrhagic septicaemia in wrasse labridae used as cleaner fish on marine atlantic salmon salmo salar l farms
Journal of Fish Diseases, 2015Co-Authors: I S Wallace, Malcolm Hall, W. Murray, K Donald, L A Munro, C C Pert, Hannah E B Stagg, Nicola BainAbstract:Viral haemorrhagic septicaemia virus (VHSV) was isolated from five species of wrasse (Labridae) used as biological controls for parasitic sea lice predominantly, Lepeophtheirus salmonis (Kroyer, 1837), on marine Atlantic salmon, Salmo salar L., farms in Shetland. As part of the epidemiological investigation, 1400 wild marine fish were caught and screened in pools of 10 for VHSV using virus isolation. Eleven pools (8%) were confirmed VHSV positive from: grey gurnard, Eutrigla gurnardus L.; Atlantic herring, Clupea harengus L.; Norway pout, Trisopterus esmarkii (Nilsson); plaice, Pleuronectes platessa L.; sprat, Sprattus sprattus L. and whiting, Merlangius merlangus L. The isolation of VHSV from grey gurnard is the first documented report in this species. Nucleic acid sequencing of the partial nucleocapsid (N) and glycoprotein (G) genes was carried out for viral characterization. Sequence analysis confirmed that all wild isolates were genotype III the same as the wrasse and there was a close genetic similarity between the isolates from wild fish and wrasse on the farms. Infection from these local wild marine fish is the most likely source of VHSV isolated from wrasse on the fish farms.
Ole Ritzau Eigaard - One of the best experts on this subject based on the ideXlab platform.
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A netting-based alternative to rigid sorting grids in the small-meshed Norway pout (Trisopterus esmarkii) trawl fishery.
PloS one, 2021Co-Authors: Ole Ritzau Eigaard, Bent Herrmann, Jordan P. Feekings, Ludvig Ahm Krag, Claus Reedtz SparrevohnAbstract:A new bycatch reduction device, termed "Excluder", is presented as an alternative to a traditional rigid sorting grid, mandatory in the small-meshed Norway Pout (Trisopterus esmarkii) trawl fishery in the North Sea. The fishery is a high-volume fishery with large vessels, large demersal trawls and catches up to 100 tons per haul of this small forage fish. The Excluder is a 30 m long netting-based sorting system, developed to reduce bycatch (70 mm square meshes) and improving on board gear-handling and safety. The Excluder was tested against a 5.8 m2 standard sorting grid (35 mm bar spacing) in a twin-trawl experiment from the commercial 70 m trawler "S364 Rockall". Catch data were analysed by species and length using the catch comparison method. For all bycatch species analysed, the Excluder had significantly lower catches relative to the grid: herring (21%), whiting (6%), mackerel (5%), American plaice (70%), witch flounder (15%), and lesser silver smelt (71%). For Norway Pout there was a significant increase in the overall catch efficiency of 32%. These results are explained by a 10 cm smaller L50 (the length of fish with 50% probability of being rejected by the sorting system) of the Excluder and a 15 times larger sorting area, which reduces the risk of clogging and loss of function. With these documented effects of improved sorting and target species catch efficiency, implementation of the Excluder would improve sustainability and address two main barriers of the current Norway pout fishery that limit quota capitalization; a tendency for Norway pout to mix with herring and whiting and lowered catch rates from grid-clogging. Additionally, gear-handling and safety on board would be improved.
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Influence of grid orientation and time of day on grid sorting in a small-meshed trawl fishery for Norway pout (Trisopterus esmarkii)
Aquatic Living Resources, 2012Co-Authors: Ole Ritzau Eigaard, Bent Herrmann, J. Rasmus NielsenAbstract:A lightweight sorting grid was developed to reduce bycatch in the Danish small-meshed trawl fishery (22 mm full mesh in the cod end) for Norway pout in the North Sea. Experimental fishing with the grid demonstrated the possibility to capture Norway pout with only a minimum of unintended bycatch. Fishing with two different grid orientations, backwards and forwards-leaning, in distinct day and night hauls, resulted in an estimated release of between 88.4 and 100% of the total number of haddock (Melanogrammus aeglefinus ) and whiting (Merlangius merlangus ) entering the trawl. However, bycatch reductions were not significantly different between day and night or between grid orientations, indicating that the grid rejection of haddock and whiting is not influenced by fish behaviour. The loss of the target species, Norway pout, was low (between 5.6% and 13.7%) in comparison with the bycatch excluded, and clearly length dependent. Consequently, loss of target species would vary with the size structure of the population fished. Although results were not statistically significant, length-based analyses indicated that the grid rejection likelihood for particularly smaller Norway pout (
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influence of grid orientation and time of day on grid sorting in a small meshed trawl fishery for norway pout Trisopterus esmarkii
Aquatic Living Resources, 2012Co-Authors: Ole Ritzau Eigaard, Bent Herrmann, Rasmus J NielsenAbstract:A lightweight sorting grid was developed to reduce bycatch in the Danish small-meshed trawl fishery (22 mm full mesh in the cod end) for Norway pout in the North Sea. Experimental fishing with the grid demonstrated the possibility to capture Norway pout with only a minimum of unintended bycatch. Fishing with two different grid orientations, backwards and forwards-leaning, in distinct day and night hauls, resulted in an estimated release of between 88.4 and 100% of the total number of haddock (Melanogrammus aeglefinus ) and whiting (Merlangius merlangus ) entering the trawl. However, bycatch reductions were not significantly different between day and night or between grid orientations, indicating that the grid rejection of haddock and whiting is not influenced by fish behaviour. The loss of the target species, Norway pout, was low (between 5.6% and 13.7%) in comparison with the bycatch excluded, and clearly length dependent. Consequently, loss of target species would vary with the size structure of the population fished. Although results were not statistically significant, length-based analyses indicated that the grid rejection likelihood for particularly smaller Norway pout (<16 cm) was higher when fishing with the forwards-leaning grid during the night; this might be explained by behavioural and visual aspects of the fish-grid encounter process for Norway pout.
Bruno Ernande - One of the best experts on this subject based on the ideXlab platform.
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North Sea saithe Pollachius virens growth in relation to food availability, density dependence and temperature
Marine Ecology Progress Series, 2016Co-Authors: Xochitl Cormon, Bruno Ernande, Alexander Kempf, Youen Vermard, Paul MarchalAbstract:North Sea saithe Pollachius virens, a major top predator in the area, supports the fishery economy of several European countries. However, recent stock assessments suggested a decrease in spawning stock biomass along with a decline in saithe mean weight-at-ages. In this context, we investigated North Sea saithe growth characteristics at the population level. First, saithe annual weight increments and age-length relationships were studied. Modelling of saithe age-length relationships was carried out using (1) the traditional von Bertalanffy growth function model, (2) the Verhulst logistic model and (3) an empirical linear model. Second, the effects of environmental factors on saithe growth were investigated. Explanatory environmental factors included food availability, represented by the total biomass of Norway pout Trisopterus esmarkii; intraspecific competition, i.e. density dependence, represented by saithe abundance; and temperature. This study revealed that the Verhulst logistic model was the best descriptor of saithe growth and that density dependence and food availability had significant effects on the saithe growth coefficient, while no effect of temperature was shown. We suggest that reduced food availability and increased competition may explain the recent decrease in the saithe growth coefficient.
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Temporal trends in age and size at maturation of four North Sea gadid species: cod, haddock, whiting and Norway pout
Marine Ecology Progress Series, 2014Co-Authors: Lise Marty, Marie-joëlle Rochet, Bruno ErnandeAbstract:Younger ages and smaller sizes at maturation have been observed in commercial fish stocks over the last century. We establish that age and length at 50% proportion mature (i.e. the proportion of mature individuals in a population or the probability that an individual is mature) decreased from the 1970s to the 2000s in North Sea cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus, but not in Norway pout Trisopterus esmarkii. The potential contributions of demography, phenotypic plasticity and evolution to these trends were assessed. First, maturation trends were extricated from demographic effects and growth-dependent plasticity by estimating probabilistic maturation reaction norms (PMRNs). PMRN midpoints have significantly shifted downwards at most ages for cod, haddock and whiting, but not for Norway pout. Second, increased temperature and food abundance, loosened trophic competition and relaxed social pressure may also trigger growth-independent plasticity in maturation. Principal component regression of PMRN midpoints on annual estimates of relevant environmental vari- ables exhibiting a temporal trend suggest that, despite some evidence of environmental effects, PMRN trends were mostly independent of growth-independent plasticity in haddock, whiting and male cod, but not in female cod. According to these findings, evolution of maturation, potentially in response to fishing, is plausible in haddock, whiting and male cod, but unlikely for Norway pout, and does not explain trends in female cod maturation. In agreement with life-history theory, the maturation response was larger in fast-growing, late- and large-maturing species exhibiting moderate reproductive effort.
