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
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
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 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.
