Fish behaviour affects the performance of selection devices in fishing gears.Traditionally,fish behaviour in relation to selection devices is assessed by direct observation.However,this approach has limitations,and th...Fish behaviour affects the performance of selection devices in fishing gears.Traditionally,fish behaviour in relation to selection devices is assessed by direct observation.However,this approach has limitations,and the observations are not explicitly incorporated in the selectivity models.Further,underwater observations and quantification of fish behaviour can be challenging.In this study we outline and use an indirect method to explicitly incorporate and quantify fish behaviour in trawl selectivity analysis.We use a set of structural models,which are based on modelling the actual processes believed to determine the size selection of the device,to discern which behaviours are most likely to explain the selectivity process.By bootstrapping we assess how confident we can be in the choice of a specific structural model and on discerning the associated behavioural aspects.We collected size selectivity data in the Barents Sea demersal trawl fishery targeting gadoids,where the use of a sorting grid is compulsory.Using our modelling approach,we obtained deeper understanding of which behavioural processes most likely affect size selectivity in the sorting grids tested.Our approach can be applied to other fishing gears to understand and quantify fish behaviour in relation to size selectivity.展开更多
Flatfish constitute a substantial proportion of the catch in several demersal trawl fisheries across the globe.Therefore,knowledge on how to discriminate between the individuals that are to be captured or released,by ...Flatfish constitute a substantial proportion of the catch in several demersal trawl fisheries across the globe.Therefore,knowledge on how to discriminate between the individuals that are to be captured or released,by size,is important for the sustainability of exploited stocks.Using European plaice(Pleuronectes platessa),flounder(Platichthys flesus),and dab(Limanda limanda)as case-study species,here we investigate how flatfish are selected in trawl codends by experimentally testing the influence of mesh geometry,and its variability,on size selection.Both diamond-mesh and square-mesh codends were tested,as well as three codends where the mesh shape was fixed to minimize its variation during fishing.The most discriminating size selectivity was found with fixed mesh geometry,revealing that variability in mesh openness negatively affects the selectivity of flatfish.Our results further demonstrate that the risk of retaining undersized flatfish tends to increase with increasing mesh opening angle in diamond-mesh codends.Our results also confirm that when fishing with codends of the same nominal mesh size,the square-mesh codend retains significantly higher proportions of undersized flatfish than the traditional diamond-mesh.展开更多
In the Barents Sea commercial snow crab(Chionoecetes opilio)fishery,an increase in catch efficiency of the conical pots is important for the profitability of the industry.Light emitting diodes(LEDs)have previously bee...In the Barents Sea commercial snow crab(Chionoecetes opilio)fishery,an increase in catch efficiency of the conical pots is important for the profitability of the industry.Light emitting diodes(LEDs)have previously been tested for increasing catch efficiency of the snow crab pots.These earlier experiments have shown varying results ranging from large increase in snow crab catches to no significant effect.These experiments have used different pot soaking times;however,the soaking time might affect the impact of LEDs on catch efficiency.In commercial snow crab fishery,the pot soak time is varying which has not been considered in earlier experiments testing the effect of LEDs.Therefore,this study examined whether pot soaking time can explain the observed differences in relative catch efficiency of snow crab pots with and without LEDs with soak times ranging from 2 to 14 days in the Barents Sea snow crab fishery.For target sizes of snow crab(≥95 mm carapace width),results indicated an increase in catch efficiency between 10 and 30%for pots with LEDs with exception of one experiment using six days soak time.However,experimental results were subjected to large uncertainties and,except from one experiment with five days soak time,the estimated increases were nonsignificant.Furthermore,the pot soak time was not found to impact the effect of white LEDs on capture efficiency.展开更多
Gillnets are one of the most commonly used fishing gears in both marine and inland waters.Different colour filament nettings are often used in gillnets.However,the effect of gillnet colour on catch efficiency is uncle...Gillnets are one of the most commonly used fishing gears in both marine and inland waters.Different colour filament nettings are often used in gillnets.However,the effect of gillnet colour on catch efficiency is unclear for most fisheries.Therefore,in this study we investigated the effect of gillnet colour on the catch efficiency in pearlspot(Etroplus suratensis)fishery in Vembanad lake,India.Gillnet colours tested were transparent,green and blue.Results showed that in this fishery,the catch efficiency of gillnets of the three colours tested differed significantly.The highest catch efficiency of pearlspot was shown by green gillnets compared to transparent or blue netting.Specifically,green gillnets on average were estimated to be 74%more efficient compared to transparent gillnets.For the green compared to the blue gillnets,the catch efficiency was estimated to be higher by 81%.These results demonstrate that gillnet colour can be an important factor significantly affecting the catch efficiency of this fishing gear.展开更多
Sea trials to test size selectivity equipment in trawls are often limited in time because they are costly,and the results can be influenced by multiple factors that are often overlooked.In the Barents Sea gadoid trawl...Sea trials to test size selectivity equipment in trawls are often limited in time because they are costly,and the results can be influenced by multiple factors that are often overlooked.In the Barents Sea gadoid trawl fishery,the use of a size sorting grid in front of the codend is compulsory.The flexigrid,a netting section containing two flexible grids,is the most widely used grid section in this fishery.However,earlier selectivity studies with this device have shown inconclusive results.It has been speculated that the differences observed resulted from the difference in age and usage of the grid sections in the studies compared.To reveal whether potential changes in the device construction over time can lead to differences in size selection properties,we performed comparative fishing trials where we compared a brand new flexigrid section and a well-used flexigrid section used continuously by a commercial trawler for approximately four years.The results showed that the new flexigrid released significantly more cod below~60 cm than the used flexigrid.However,when the grids were fished with a subsequent diamond mesh codend,there was no difference in the overall selectivity of the two gears,meaning that the size selectivity in the codend compensates for the potential reduction in selectivity performance of the grids.This study shows the importance of considering the age and earlier use of size selection devices like sorting grids before they are compared with other devices,as their size selection properties can change significantly over time and with use.展开更多
The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen oper...The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen operating along the northwest coast of India,and the cover codend method was employed to determine codend selectivity.Along with the changes in the length at 50%retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends,indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch.The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes,however,it is observed that individuals at commercial length are also lost.The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species,given its estimated length at first sexual maturity of 61.2 cm.This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India.Results of the study will help as a baseline for gear-based regulations in the region.展开更多
The size selectivity and usability of three codends were quantified and compared for the first time in the inshore Northern shrimp(Pandalus borealis)trawl fishery of Iceland using the covered codend method:a conventio...The size selectivity and usability of three codends were quantified and compared for the first time in the inshore Northern shrimp(Pandalus borealis)trawl fishery of Iceland using the covered codend method:a conventional diamond-mesh codend(T0),conventional square-mesh codend(T45),and a 90◦turned mesh codend(T90)constructed of four panels and with shortened lastridge ropes.Fishers,wanting to increase the average-individual size of captured shrimp,had requested the T90 codend to be compared with conventional codends for consideration in the fishery.Results showed that,on average,the T45 and T90 codends had better size selectivity than the T0 codend in terms of releasing individuals smaller than 13 mm carapace length(Minimum References Size;MRS).The T90 codend retained significantly less Northern shrimps between 9 and 19 mm than the T0 codend and between 15 and 19 mm than the T45 codend.No significant difference of size selectivity between T45 and T0 codends was observed.All three codends presented high retention ratios of Northern shrimps above MRS(>63%)for the population encountered.However,the T0 codend was not effective at sorting out small Northern shrimps;at least 86%of Northern shrimps smaller than 13 mm were retained in the T0 codend if encountered.Catches from T45 and T90 codends had a lower proportion of shrimp below MRS.Since discarding of undersized Northern shrimps is prohibited in Iceland and fishers wanted to catch on average larger shrimp,using the novel T90 codend would enable fishers to use their quotas more efficiently.展开更多
基金part of the project FHF 901633"Development of selectivity systems for gadoid trawls".
文摘Fish behaviour affects the performance of selection devices in fishing gears.Traditionally,fish behaviour in relation to selection devices is assessed by direct observation.However,this approach has limitations,and the observations are not explicitly incorporated in the selectivity models.Further,underwater observations and quantification of fish behaviour can be challenging.In this study we outline and use an indirect method to explicitly incorporate and quantify fish behaviour in trawl selectivity analysis.We use a set of structural models,which are based on modelling the actual processes believed to determine the size selection of the device,to discern which behaviours are most likely to explain the selectivity process.By bootstrapping we assess how confident we can be in the choice of a specific structural model and on discerning the associated behavioural aspects.We collected size selectivity data in the Barents Sea demersal trawl fishery targeting gadoids,where the use of a sorting grid is compulsory.Using our modelling approach,we obtained deeper understanding of which behavioural processes most likely affect size selectivity in the sorting grids tested.Our approach can be applied to other fishing gears to understand and quantify fish behaviour in relation to size selectivity.
基金the European Maritime and Fisheries Fund(EMFF)and the Ministry of Food,Agriculture and Fisheries of Denmark(Ministeriet for Fødevarer,Landbrug og Fiskeri)as part of the projects(FastTrack II–Sustainable,cost effective and responsive gear solutions under the landing obligation(33112-P-18-051)and Udvikling af SELEKTive redskaber og teknologier til kommercielle fiskerier(SELEKT)).
文摘Flatfish constitute a substantial proportion of the catch in several demersal trawl fisheries across the globe.Therefore,knowledge on how to discriminate between the individuals that are to be captured or released,by size,is important for the sustainability of exploited stocks.Using European plaice(Pleuronectes platessa),flounder(Platichthys flesus),and dab(Limanda limanda)as case-study species,here we investigate how flatfish are selected in trawl codends by experimentally testing the influence of mesh geometry,and its variability,on size selection.Both diamond-mesh and square-mesh codends were tested,as well as three codends where the mesh shape was fixed to minimize its variation during fishing.The most discriminating size selectivity was found with fixed mesh geometry,revealing that variability in mesh openness negatively affects the selectivity of flatfish.Our results further demonstrate that the risk of retaining undersized flatfish tends to increase with increasing mesh opening angle in diamond-mesh codends.Our results also confirm that when fishing with codends of the same nominal mesh size,the square-mesh codend retains significantly higher proportions of undersized flatfish than the traditional diamond-mesh.
基金grateful to the academic editor and reviewers for their valuable comments,which have improved our manuscript.This project was funded by the Norwegian Research Council(CRABTECH Ⅱ,grant number:296044).
文摘In the Barents Sea commercial snow crab(Chionoecetes opilio)fishery,an increase in catch efficiency of the conical pots is important for the profitability of the industry.Light emitting diodes(LEDs)have previously been tested for increasing catch efficiency of the snow crab pots.These earlier experiments have shown varying results ranging from large increase in snow crab catches to no significant effect.These experiments have used different pot soaking times;however,the soaking time might affect the impact of LEDs on catch efficiency.In commercial snow crab fishery,the pot soak time is varying which has not been considered in earlier experiments testing the effect of LEDs.Therefore,this study examined whether pot soaking time can explain the observed differences in relative catch efficiency of snow crab pots with and without LEDs with soak times ranging from 2 to 14 days in the Barents Sea snow crab fishery.For target sizes of snow crab(≥95 mm carapace width),results indicated an increase in catch efficiency between 10 and 30%for pots with LEDs with exception of one experiment using six days soak time.However,experimental results were subjected to large uncertainties and,except from one experiment with five days soak time,the estimated increases were nonsignificant.Furthermore,the pot soak time was not found to impact the effect of white LEDs on capture efficiency.
基金financed by the Research Council of Norway(grant number:310008).
文摘Gillnets are one of the most commonly used fishing gears in both marine and inland waters.Different colour filament nettings are often used in gillnets.However,the effect of gillnet colour on catch efficiency is unclear for most fisheries.Therefore,in this study we investigated the effect of gillnet colour on the catch efficiency in pearlspot(Etroplus suratensis)fishery in Vembanad lake,India.Gillnet colours tested were transparent,green and blue.Results showed that in this fishery,the catch efficiency of gillnets of the three colours tested differed significantly.The highest catch efficiency of pearlspot was shown by green gillnets compared to transparent or blue netting.Specifically,green gillnets on average were estimated to be 74%more efficient compared to transparent gillnets.For the green compared to the blue gillnets,the catch efficiency was estimated to be higher by 81%.These results demonstrate that gillnet colour can be an important factor significantly affecting the catch efficiency of this fishing gear.
基金the Norwegian Fisheries and Aquaculture Research Fund(project number 901633)for funding the project.
文摘Sea trials to test size selectivity equipment in trawls are often limited in time because they are costly,and the results can be influenced by multiple factors that are often overlooked.In the Barents Sea gadoid trawl fishery,the use of a size sorting grid in front of the codend is compulsory.The flexigrid,a netting section containing two flexible grids,is the most widely used grid section in this fishery.However,earlier selectivity studies with this device have shown inconclusive results.It has been speculated that the differences observed resulted from the difference in age and usage of the grid sections in the studies compared.To reveal whether potential changes in the device construction over time can lead to differences in size selection properties,we performed comparative fishing trials where we compared a brand new flexigrid section and a well-used flexigrid section used continuously by a commercial trawler for approximately four years.The results showed that the new flexigrid released significantly more cod below~60 cm than the used flexigrid.However,when the grids were fished with a subsequent diamond mesh codend,there was no difference in the overall selectivity of the two gears,meaning that the size selectivity in the codend compensates for the potential reduction in selectivity performance of the grids.This study shows the importance of considering the age and earlier use of size selection devices like sorting grids before they are compared with other devices,as their size selection properties can change significantly over time and with use.
文摘The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen operating along the northwest coast of India,and the cover codend method was employed to determine codend selectivity.Along with the changes in the length at 50%retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends,indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch.The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes,however,it is observed that individuals at commercial length are also lost.The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species,given its estimated length at first sexual maturity of 61.2 cm.This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India.Results of the study will help as a baseline for gear-based regulations in the region.
文摘The size selectivity and usability of three codends were quantified and compared for the first time in the inshore Northern shrimp(Pandalus borealis)trawl fishery of Iceland using the covered codend method:a conventional diamond-mesh codend(T0),conventional square-mesh codend(T45),and a 90◦turned mesh codend(T90)constructed of four panels and with shortened lastridge ropes.Fishers,wanting to increase the average-individual size of captured shrimp,had requested the T90 codend to be compared with conventional codends for consideration in the fishery.Results showed that,on average,the T45 and T90 codends had better size selectivity than the T0 codend in terms of releasing individuals smaller than 13 mm carapace length(Minimum References Size;MRS).The T90 codend retained significantly less Northern shrimps between 9 and 19 mm than the T0 codend and between 15 and 19 mm than the T45 codend.No significant difference of size selectivity between T45 and T0 codends was observed.All three codends presented high retention ratios of Northern shrimps above MRS(>63%)for the population encountered.However,the T0 codend was not effective at sorting out small Northern shrimps;at least 86%of Northern shrimps smaller than 13 mm were retained in the T0 codend if encountered.Catches from T45 and T90 codends had a lower proportion of shrimp below MRS.Since discarding of undersized Northern shrimps is prohibited in Iceland and fishers wanted to catch on average larger shrimp,using the novel T90 codend would enable fishers to use their quotas more efficiently.
