There has been an increasing emphasis on reducing the environmental impacts of penaeid trawls by modifying their anterior sections.In one Australian estuary,this approach has culminated in a new generic trawl comprisi...There has been an increasing emphasis on reducing the environmental impacts of penaeid trawls by modifying their anterior sections.In one Australian estuary,this approach has culminated in a new generic trawl comprising a slightly smaller mesh size,and steeper and shorter side panels than traditional trawls,combined with a top panel extending forwards of the bottom panel(termed‘lead-ahead’)and no headline floats.This study sought to investigate if an additional simple,cumulative modification(tickler chain)might help promote adoption of the new trawl,via improved penaeid catches.Six volunteer fishers towing pairs of either the traditional or new trawls in double rigs were asked if an observer could accompany fishing trips,and alternately attach a light tickler chain(~3 kg)anterior to the ground gear of one trawl.Regardless of the trawl design,the tickler chains significantly increased the catch weights of penaeids,but relatively more so in the new trawls(by 1.11×vs 1.08×).The tickler chains also significantly increased the number and weight of total bycatch in the traditional trawls(by up to 1.22×),but not in the new trawls-although there were variable species-specific effects.In terms of total effects,the data support using tickler chains to increase the efficiency of the new trawls and their cumulative benefits,and could be promoted to facilitate broader inter-and intra-fleet adoption.展开更多
In south-eastern Australia,the same baited,round traps(comprising 50–57-mm mesh netting)are used to target giant mud,Scylla serrata and blue swimmer crabs,Portunus armatus in spatially separated fisheries.Both fisher...In south-eastern Australia,the same baited,round traps(comprising 50–57-mm mesh netting)are used to target giant mud,Scylla serrata and blue swimmer crabs,Portunus armatus in spatially separated fisheries.Both fisheries are characterised by the common,problematic discarding of undersized portunids(<85 and 65 mm carapace length;CL for S.serrata and P.armatus)and fish(yellowfin bream,Acanthopagrus australis).This poor selectivity was addressed here in two experiments assessing the utility of(1)traps partially or completely covered in larger mesh(91 mm to match the minimum legal size of the smaller P.armatus),and then(2)any cumulative benefits of fitting species-specific escape gaps.In experiment 1,there were no differences among catches of legal-sized portunids associated with either partial,or complete trap coverage with larger mesh.Irrespective of mesh coverage,both designs of 91-mm traps also retained significantly fewer(by up to 42%)undersized P.armatus and A.australis.In experiment 2,replicate traps completely covered in 91-mm mesh were tested against conventional traps comprising 56-mm mesh,and traps with the same mesh sizes,but also three escape gaps configured for either S.serrata(46×120 mm)or P.armatus(36×120 mm)(i.e.four treatments in total).All modified traps maintained catches of legal-sized S.serrata,and only the 91-mm traps with escape gaps caught fewer legal-sized P.armatus.Fewer undersized S.serrata,P.armatus and A.australis(mean catches reduced by up to 49%)were retained in all larger-meshed than small-meshed traps,and in all of those traps with escape gaps(by up to 95%)than without.While there were no significant cumulative benefits of escape gaps in largermeshed traps(measured by a statistical interaction),there was a trend of fewer unwanted catches overall.These data support configuring portunid traps with mesh sizes matching the morphology of the smallest legal-sized target species.But,simply retroactively fitting escape gaps in existing,smaller-meshed traps will also realize positive selectivity benefits.展开更多
基金This study was funded by the New South Wales Department of Primary Industries。
文摘There has been an increasing emphasis on reducing the environmental impacts of penaeid trawls by modifying their anterior sections.In one Australian estuary,this approach has culminated in a new generic trawl comprising a slightly smaller mesh size,and steeper and shorter side panels than traditional trawls,combined with a top panel extending forwards of the bottom panel(termed‘lead-ahead’)and no headline floats.This study sought to investigate if an additional simple,cumulative modification(tickler chain)might help promote adoption of the new trawl,via improved penaeid catches.Six volunteer fishers towing pairs of either the traditional or new trawls in double rigs were asked if an observer could accompany fishing trips,and alternately attach a light tickler chain(~3 kg)anterior to the ground gear of one trawl.Regardless of the trawl design,the tickler chains significantly increased the catch weights of penaeids,but relatively more so in the new trawls(by 1.11×vs 1.08×).The tickler chains also significantly increased the number and weight of total bycatch in the traditional trawls(by up to 1.22×),but not in the new trawls-although there were variable species-specific effects.In terms of total effects,the data support using tickler chains to increase the efficiency of the new trawls and their cumulative benefits,and could be promoted to facilitate broader inter-and intra-fleet adoption.
基金This study was funded by Hunter Local Land Services and the NSW Department of Primary Industries,and would not have been possible without the assistance of Wallis Lake commercial fishers,and especially,Malcolm,Adrian and Danny.
文摘In south-eastern Australia,the same baited,round traps(comprising 50–57-mm mesh netting)are used to target giant mud,Scylla serrata and blue swimmer crabs,Portunus armatus in spatially separated fisheries.Both fisheries are characterised by the common,problematic discarding of undersized portunids(<85 and 65 mm carapace length;CL for S.serrata and P.armatus)and fish(yellowfin bream,Acanthopagrus australis).This poor selectivity was addressed here in two experiments assessing the utility of(1)traps partially or completely covered in larger mesh(91 mm to match the minimum legal size of the smaller P.armatus),and then(2)any cumulative benefits of fitting species-specific escape gaps.In experiment 1,there were no differences among catches of legal-sized portunids associated with either partial,or complete trap coverage with larger mesh.Irrespective of mesh coverage,both designs of 91-mm traps also retained significantly fewer(by up to 42%)undersized P.armatus and A.australis.In experiment 2,replicate traps completely covered in 91-mm mesh were tested against conventional traps comprising 56-mm mesh,and traps with the same mesh sizes,but also three escape gaps configured for either S.serrata(46×120 mm)or P.armatus(36×120 mm)(i.e.four treatments in total).All modified traps maintained catches of legal-sized S.serrata,and only the 91-mm traps with escape gaps caught fewer legal-sized P.armatus.Fewer undersized S.serrata,P.armatus and A.australis(mean catches reduced by up to 49%)were retained in all larger-meshed than small-meshed traps,and in all of those traps with escape gaps(by up to 95%)than without.While there were no significant cumulative benefits of escape gaps in largermeshed traps(measured by a statistical interaction),there was a trend of fewer unwanted catches overall.These data support configuring portunid traps with mesh sizes matching the morphology of the smallest legal-sized target species.But,simply retroactively fitting escape gaps in existing,smaller-meshed traps will also realize positive selectivity benefits.
