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Niels Madsen - One of the best experts on this subject based on the ideXlab platform.
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development of a codend concept to improve size selectivity of Nephrops Nephrops norvegicus in a multi species fishery
Fisheries Research, 2011Co-Authors: Rikke Petri Frandsen, Bent Herrmann, Niels Madsen, Ludvig Ahm KragAbstract:Abstract Species-specific differences in morphology and minimum landing size will often result in high discard rates in mixed-species fisheries. This is the case in the Danish Nephrops -directed fishery and the aim of this study was to improve the size selectivity of Nephrops without increasing catch below minimum landing size (MLS) of cod ( Gadus morhua ) and plaice ( Pleuronectes platessa ). A new codend concept combining square meshes and diamond meshes in a four-panel configuration was developed and tested in the Kattegat and Skagerrak. A 5 m long 70 mm square-mesh panel was inserted in the lower panel of the codend to increase size selectivity of Nephrops while the remaining three panels were made of standard 90 mm diamond-mesh netting to maintain selectivity of plaice and cod. The concept succeeded in significantly ( p L 50 of Nephrops without increasing discards of either plaice or cod. When using the new codend concept, expected numbers of Nephrops below MLS (carapace length = 40 mm) were reduced by approximately 37% but the expected weight of marketable catch was also reduced by 21%. The concept was adjusted and tested in a second experiment so that fishing using the new net configuration would remain commercially viable. This experiment indicated that size selectivity of Nephrops could be adjusted by changing the square-mesh panel but differences in mean selection between the gears were insignificant. We introduce a new analytical approach with increased statistical power to detect differences in selection parameters between different codends.
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A simulation-based attempt to quantify the morphological component of size selection of Nephrops norvegicus in trawl codends
Fisheries Research, 2010Co-Authors: Rikke Petri Frandsen, Bent Herrmann, Niels MadsenAbstract:The selectivity for Nephrops (Nephrops norvegicus) in trawl codends generally is poor and the lack of steepness of the selection curve results in high discard rates and/or loss of legal-sized catch. This poor codend selectivity often is attributed to the irregular shape of Nephrops, which to some extent characterizes the problem as insoluble. In the present study, the FISHSELECT methodology was used to examine the selection process of the species in order to identify ways to improve selectivity. The use of three different modes of orientation for contact (contact modes) with the codend meshes explained most of the characteristics of the selection curves for Nephrops obtained experimentally. The contact mode with the smallest cross-section was optimal for mesh penetration and, when evaluated against experimental data, 87.5% of all Nephrops encountering the gear were estimated to meet the netting in this contact mode. The range of configurations of the meshes (e.g., opening angles in the diamond mesh netting) was determinative for the selectivity, and the selective process for Nephrops was found to take place along the entire length of the codend. Simulating selectivity in a diamond mesh codend in which the closed meshes in the forward part of the codend were replaced by more open meshes revealed that the selectivity for Nephrops can be efficiently improved.
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Evaluation of three levels of selective devices relevant to management of the Danish Kattegat―Skagerrak Nephrops fishery
Fisheries Research, 2009Co-Authors: Rikke Petri Frandsen, René Holst, Niels MadsenAbstract:Abstract This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops , plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals. We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops , plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend. The SMP significantly ( p Nephrops .
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evaluation of three levels of selective devices relevant to management of the danish kattegat skagerrak Nephrops fishery
Fisheries Research, 2009Co-Authors: Rikke Petri Frandsen, René Holst, Niels MadsenAbstract:Abstract This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops , plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals. We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops , plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend. The SMP significantly ( p Nephrops .
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Selectivity experiments with escape windows in the North Sea Nephrops (Nephrops norvegicus) trawl fishery
Fisheries Research, 1999Co-Authors: Niels Madsen, Thomas Moth-poulsen, René Holst, D. WilemanAbstract:Abstract Selectivity experiments were carried out in the northern North Sea at the Fladen Ground and the East Ground from a Danish commercial vessel. A conventional 70 mm Nephrops codend and a similar codend with a 90 mm square mesh panel window inserted in the top panel were tested simultaneously in a twin trawl rig. Selectivity parameters and differences in catches of the target species Nephrops and the by-catch species whiting, haddock and cod were estimated. The logistic function was found to give the best description of fish selection ogives, whereas the asymmetric complementary loglog function described Nephrops selection best. The Fryer model was used to describe and compare the selection ogives for haddock, whiting, cod and Nephrops in the two codends. Due to low catches of cod and Nephrops only four out of 11 hauls could be used for modelling the selection of these two species. Selection factor and selection range were larger for the window codend for all fish species. The codend catch size had a significant negatively correlated influence on l50 and selection range for whiting in the window codend. There were large significant reductions in numbers of cod and haddock under the Danish MLS with the window codend. Catches of small cod, however, were low. Very few whiting under MLS were retained in either codend but there was a large significant reduction in individuals over MLS with the window codend. A large proportion of the Nephrops in the codends were under MLS. A reduction in catch weight of Nephrops over MLS was found for the window codend, but catches of Nephrops were low for several hauls.
Rikke Petri Frandsen - One of the best experts on this subject based on the ideXlab platform.
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development of a codend concept to improve size selectivity of Nephrops Nephrops norvegicus in a multi species fishery
Fisheries Research, 2011Co-Authors: Rikke Petri Frandsen, Bent Herrmann, Niels Madsen, Ludvig Ahm KragAbstract:Abstract Species-specific differences in morphology and minimum landing size will often result in high discard rates in mixed-species fisheries. This is the case in the Danish Nephrops -directed fishery and the aim of this study was to improve the size selectivity of Nephrops without increasing catch below minimum landing size (MLS) of cod ( Gadus morhua ) and plaice ( Pleuronectes platessa ). A new codend concept combining square meshes and diamond meshes in a four-panel configuration was developed and tested in the Kattegat and Skagerrak. A 5 m long 70 mm square-mesh panel was inserted in the lower panel of the codend to increase size selectivity of Nephrops while the remaining three panels were made of standard 90 mm diamond-mesh netting to maintain selectivity of plaice and cod. The concept succeeded in significantly ( p L 50 of Nephrops without increasing discards of either plaice or cod. When using the new codend concept, expected numbers of Nephrops below MLS (carapace length = 40 mm) were reduced by approximately 37% but the expected weight of marketable catch was also reduced by 21%. The concept was adjusted and tested in a second experiment so that fishing using the new net configuration would remain commercially viable. This experiment indicated that size selectivity of Nephrops could be adjusted by changing the square-mesh panel but differences in mean selection between the gears were insignificant. We introduce a new analytical approach with increased statistical power to detect differences in selection parameters between different codends.
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A simulation-based attempt to quantify the morphological component of size selection of Nephrops norvegicus in trawl codends
Fisheries Research, 2010Co-Authors: Rikke Petri Frandsen, Bent Herrmann, Niels MadsenAbstract:The selectivity for Nephrops (Nephrops norvegicus) in trawl codends generally is poor and the lack of steepness of the selection curve results in high discard rates and/or loss of legal-sized catch. This poor codend selectivity often is attributed to the irregular shape of Nephrops, which to some extent characterizes the problem as insoluble. In the present study, the FISHSELECT methodology was used to examine the selection process of the species in order to identify ways to improve selectivity. The use of three different modes of orientation for contact (contact modes) with the codend meshes explained most of the characteristics of the selection curves for Nephrops obtained experimentally. The contact mode with the smallest cross-section was optimal for mesh penetration and, when evaluated against experimental data, 87.5% of all Nephrops encountering the gear were estimated to meet the netting in this contact mode. The range of configurations of the meshes (e.g., opening angles in the diamond mesh netting) was determinative for the selectivity, and the selective process for Nephrops was found to take place along the entire length of the codend. Simulating selectivity in a diamond mesh codend in which the closed meshes in the forward part of the codend were replaced by more open meshes revealed that the selectivity for Nephrops can be efficiently improved.
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Evaluation of three levels of selective devices relevant to management of the Danish Kattegat―Skagerrak Nephrops fishery
Fisheries Research, 2009Co-Authors: Rikke Petri Frandsen, René Holst, Niels MadsenAbstract:Abstract This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops , plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals. We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops , plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend. The SMP significantly ( p Nephrops .
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evaluation of three levels of selective devices relevant to management of the danish kattegat skagerrak Nephrops fishery
Fisheries Research, 2009Co-Authors: Rikke Petri Frandsen, René Holst, Niels MadsenAbstract:Abstract This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops , plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals. We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops , plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend. The SMP significantly ( p Nephrops .
M Ulmestrand - One of the best experts on this subject based on the ideXlab platform.
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Species-selective Nephrops trawling: Swedish grid experiments
Fisheries Research, 2008Co-Authors: D. Valentinsson, M UlmestrandAbstract:This paper presents a summary of all catch-comparison gear tests performed between 2002 and 2006 with Nordmore-type sorting grids in the Swedish Nephrops trawl fishery in the Skagerrak and Kattegat. The overall aim was to minimise fish by-catch while maintaining catch rates for the target species, i.e. Nephrops. The results showed that a trawl fitted with a grid and a square-mesh cod-end, caught less small and marketable cod, haddock, whiting, hake and plaice than did a standard commercial trawl. For cod larger than 35 cm, the catch reduction was close to 100%. For marketable Nephrops no difference in catch amounts was detected. Results of three modified grid variants are also reported here. None of these showed convincing results in terms of better species-selectivity or superior handling characteristics than the standard grid. The results on fish by-catch reduction indicate that the Swedish grid may be a useful tool to reduce non-target mortality and to decouple Nephrops from cod and other demersal fish species under existing and future recovery plans.
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Discarding Norway lobster (Nephrops norvegicus L.) through low salinity layers – mortality and damage seen in simulation experiments
Ices Journal of Marine Science, 2004Co-Authors: R.r Harris, M UlmestrandAbstract:Harris, R. R., and Ulmestrand, M. 2004. Discarding Norway lobster (Nephrops norvegicus L.) through low salinity layers e mortality and damage seen in simulation experiments. e ICES Journal of Marine Science, 61: 127e139. The Kattegat/Skagerrak Nephrops fishery is unusual in that animals normally live in high salinities (33e34 psu) but are raised through a low salinity surface layer and, if discarded, descend back through it to the sea bed. In other open-sea Nephrops fisheries, such low salinity exposure is rare. Physiologically the species is described as being marine stenohaline, i.e. intolerant of reduced salinities, and a lower salinity limit of 29e30 for its distribution has been suggested. Using CTD data from the Anholt E hydrographic station, near to known Nephrops grounds, a knowledge of hauling times (including washing the cod-end with surface water) and of the sinking rate of Nephrops, we simulated conditions experienced by the catch in this fishery. We also included a period of emersion (air exposure) on deck during sorting or reshooting the trawl. Blood electrolytes, body mass changes and simple behavioural responses were examined before and after the simulation over a 5-day period. ‘‘Discarded’’ Nephrops experienced significant haemodilution and gained mass rapidly. Animals showed slow rates of ‘‘tail-flipping’’, or absence of responses to stimulation, in the period immediately following return to salinity 33 seawater, although many showed recovery later. Delayed effects included abdominal stiffness, swelling and further mortalities (25e42% overall). Controls (exposed to 33 psu seawater only) showed good survival and vigorous responses, even with a period of emersion. The effects of salinity exposure, which are additional to the stresses of being trawled, on the fitness of discarded animals were evaluated. Our results suggest that Nephrops discard mortality in this fishery is significantly higher than past estimates and is due to the stress of this brief exposure to low salinity surface water.
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discarding norway lobster Nephrops norvegicus l through low salinity layers mortality and damage seen in simulation experiments
Ices Journal of Marine Science, 2004Co-Authors: R.r Harris, M UlmestrandAbstract:Harris, R. R., and Ulmestrand, M. 2004. Discarding Norway lobster (Nephrops norvegicus L.) through low salinity layers e mortality and damage seen in simulation experiments. e ICES Journal of Marine Science, 61: 127e139. The Kattegat/Skagerrak Nephrops fishery is unusual in that animals normally live in high salinities (33e34 psu) but are raised through a low salinity surface layer and, if discarded, descend back through it to the sea bed. In other open-sea Nephrops fisheries, such low salinity exposure is rare. Physiologically the species is described as being marine stenohaline, i.e. intolerant of reduced salinities, and a lower salinity limit of 29e30 for its distribution has been suggested. Using CTD data from the Anholt E hydrographic station, near to known Nephrops grounds, a knowledge of hauling times (including washing the cod-end with surface water) and of the sinking rate of Nephrops, we simulated conditions experienced by the catch in this fishery. We also included a period of emersion (air exposure) on deck during sorting or reshooting the trawl. Blood electrolytes, body mass changes and simple behavioural responses were examined before and after the simulation over a 5-day period. ‘‘Discarded’’ Nephrops experienced significant haemodilution and gained mass rapidly. Animals showed slow rates of ‘‘tail-flipping’’, or absence of responses to stimulation, in the period immediately following return to salinity 33 seawater, although many showed recovery later. Delayed effects included abdominal stiffness, swelling and further mortalities (25e42% overall). Controls (exposed to 33 psu seawater only) showed good survival and vigorous responses, even with a period of emersion. The effects of salinity exposure, which are additional to the stresses of being trawled, on the fitness of discarded animals were evaluated. Our results suggest that Nephrops discard mortality in this fishery is significantly higher than past estimates and is due to the stress of this brief exposure to low salinity surface water.
Jacopo Aguzzi - One of the best experts on this subject based on the ideXlab platform.
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New monitoring technologies to produce ancillary data on Nephrops stock assessment
2019Co-Authors: Jacopo Aguzzi, Nixon Bahamon, Joan Navarro, Guiomar Rotllant, José A. García, Joaquin Del Rio, Spartacus Gomáriz, I. Masmitja, Emanuela Fanelli, Simone MariniAbstract:Working Group on Nephrops Surveys (WGNEPS), 6-8 November 2018, Lorient, France.-- 2 pages, 2 figures
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identification characterization and diel pattern of expression of canonical clock genes in Nephrops norvegicus crustacea decapoda eyestalk
PLOS ONE, 2015Co-Authors: Valerio Sbragaglia, Guiomar Rotllant, Francesco Lamanna, Audrey M Mat, Silvia Joly, Valerio Ketmaier, Horacio O De La Iglesia, Jacopo AguzziAbstract:The Norway lobster, Nephrops norvegicus, is a burrowing decapod with a rhythmic burrow emergence (24 h) governed by the circadian system. It is an important resource for European fisheries and its behavior deeply affects its availability. The current knowledge of Nephrops circadian biology is phenomenological as it is currently the case for almost all crustaceans. In attempt to elucidate the putative molecular mechanisms underlying circadian gene regulation in Nephrops, we used a transcriptomics approach on cDNA extracted from the eyestalk, a structure playing a crucial role in controlling behavior of decapods. We studied 14 male lobsters under 12–12 light-darkness blue light cycle. We used the Hiseq 2000 Illumina platform to sequence two eyestalk libraries (under light and darkness conditions) obtaining about 90 millions 100-bp paired-end reads. Trinity was used for the de novo reconstruction of transcriptomes; the size at which half of all assembled bases reside in contigs (N50) was equal to 1796 (light) and 2055 (darkness). We found a list of candidate clock genes and focused our attention on canonical ones: timeless, period, clock and bmal1. The cloning of assembled fragments validated Trinity outputs. The putative Nephrops clock genes showed high levels of identity (blastx on NCBI) with known crustacean clock gene homologs such as Eurydice pulchra (period: 47%, timeless: 59%, bmal1: 79%) and Macrobrachium rosenbergii (clock: 100%). We also found a vertebrate-like cryptochrome 2. RT-qPCR showed that only timeless had a robust diel pattern of expression. Our data are in accordance with the current knowledge of the crustacean circadian clock, reinforcing the idea that the molecular clockwork of this group shows some differences with the established model in Drosophila melanogaster.
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Video-image processing applied to the analysis of the behaviour of deep-water lobsters (Nephrops norvegicus)
OCEANS'10 IEEE SYDNEY, 2010Co-Authors: Sergi Pons, Jaume Piera, Jacopo AguzziAbstract:In this study, we show the results of applying two automated data processing methods to a set of videos previously used to manually monitor the period and the phase of activity rhythms of the deep-water Norway lobster, Nephrops norvegicus, a species of elevated commercial fishery value. Present data are consistent with published findings on Nephrops norvegicus activity rhythms both in the laboratory and the field.
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the influence of light availability and predatory behavior of the decapod crustacean Nephrops norvegicus on the activity rhythms of continental margin prey decapods
Marine Ecology, 2009Co-Authors: Jacopo Aguzzi, Nixon Bahamon, Leonardo MarottaAbstract:The day–night cycle is one of the strongest geophysical cycles modulating species’ behavioral rhythms. However, in deep-water continental margins, where light intensity decreases over depth, interspecific competition may alter behavioral responses to day–night cycles. The burrowing decapod crustacean Nephrops norvegicus is a large-size predator in benthic communities, exerting despotic territorial behavior. In this study, we analysed how the effect of light intensity cycles on decapod behavioral rhythms is reduced as one moves from shelves to slopes. In the Western Mediterranean, the predatory behavior and interspecific competition for substrate use of Nephrops increases moving from the shelf (100–110 m) to the slope (400–430 m). Vector fitting and generalized additive models were used to assess the effect of light intensity and behavioral rhythms of N. norvegicus on the temporal variation of prey decapods co-occurring in trawl tow catches carried out on the shelf and the slope during October 1999 and June 2000. The combination of diel variations in light intensity and N. norvegicus abundance influences the activity rhythms of prey decapods in a depth- and seasonal-dependent manner. Light modulation is stronger on the shelf and weaker on the slope, where Nephrops population size is greater. Although present regression analysis does not necessarily imply a direct cause– effect relationship between rhythms of predators and prey, we suggest that Nephrops alters the temporal patterning in the behavior of its prey on the slope, where light intensity is reduced. This alteration is stronger in endobenthic species than in benthopelagic species; the former rely on bottom substrate for the expression of behavioral rhythms, experiencing stronger interspecific competitions with Nephrops at time of activity.
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A history of recent advancements on Nephrops norvegicus behavioral and physiological rhythms
Reviews in Fish Biology and Fisheries, 2008Co-Authors: Jacopo Aguzzi, Francesc SardàAbstract:Biological rhythms are a widespread feature of living organisms, being expressed at any level of their organization. Behavioral and physiological rhythms can affect the results on species stock assessment when the timing of sampling is not taken into account. That timing is of importance since animals may be present or not in a certain area of sampling depending on their activity cycle. As an example of this, the rhythmic behavior and physiology of one of the most commercially important European decapods, the Norway lobster ( Nephrops norvegicus ) was studied. These rhythms affect its commercial catchability at a diel and at a seasonal scale. Nephrops inhabits muddy bottoms where animals dig burrows that save them from the trawl tow capture when occupied. Catch patterns have been widely used as proxy of activity rhythms of populations of different depths. Catches show a modulation upon the day-night cycle since animals emerge under optimum environmental illumination in order to feed. Emergence is also affected in a not fully clarified manner by other variables of environmental and demographic nature (e.g. food presence, hunger state, sex, size, reproductive stage, territorialism and mating). All these features make Nephrops a good model of reference for studies on biological rhythms of other commercially important deep water decapods in relation to their ecological context. In this review, we summarize the actual knowledge on Nephrops behavioral and physiological rhythms. We will compare data obtained from laboratory tests on single individuals with data obtained from trawling of populations of different depths. We will also describe some new hypotheses on the rhythmic regulation of the species behaviour, as well as potential scenarios for future research.
A. S. Revill - One of the best experts on this subject based on the ideXlab platform.
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Gear technology in Nephrops trawl fisheries
Reviews in Fish Biology and Fisheries, 2008Co-Authors: T. L. Catchpole, A. S. RevillAbstract:Nets with a small mesh size are required to catch Nephrops norvegicus , consequently large quantities of small whitefish are also caught, and much of this bycatch is undersized and is discarded dead. The main bycatch species are whiting ( Merlangius merlangus ), haddock ( Melanogrammus aeglefinus ) and cod ( Gadus morhua ). Here we summarize the known behavioural reactions of these species towards conventional trawls and review the results of using different trawl modifications to increase selectivity of Nephrops trawls. The trawl modifications are categorised as separator grids, separator and guiding panels, square-mesh panels, capture avoidance designs and codend modification. Finally, the extent to which these developments have been legislated for is discussed including the conditions under which new gear regulations have been introduced. Haddock and whiting rise during the trawling process facilitating their separation from Nephrops and escape, however the behaviour of small fish of these species is less consistent. Cod and Nephrops remain on bottom of the trawl, so to separate these species requires some physical filtering process. Overall, there is currently sufficient technical ability to improve selectivity in Nephrops trawls. The design of choice is dependent on the objectives of managers; for reducing discards but retaining marketable fish, square-mesh panels offer the most useful tool; to eliminate all bycatch and create a single-species fishery, grids and traditional Nephrops trawls show most potential. Whatever the objectives of the new measures, it is likely that a short-term economic impact will follow, and some form of incentive may be required to implement effective measures. A voluntary uptake of new measures by industry is preferable, however, to date, restrictions on fishing opportunities have been necessary to introduce innovative gear designs.