Portunids are important to recreational fisheries in Australia and typically are harvested by baited gears.Most of these baited gears are considered environmentally benign,although small conical hoop(tangle)nets fishe...Portunids are important to recreational fisheries in Australia and typically are harvested by baited gears.Most of these baited gears are considered environmentally benign,although small conical hoop(tangle)nets fished in southeastern Australia sometimes are damaged and lose twine,which becomes marine debris.Substituting conventional multifilament polyamide(PA)twine with alternative multi-monofilament and monofilament PA twines in hoop nets can dramatically reduce marine debris,but there remain unanswered questions concerning the relative fishing power of alternative twines among derelict hoop nets.This study addresses the shortfall in data by comparing the efficiencies and damage to replicate hoop nets made from the three twines and left to fish for short(one and two days),medium(three to five days)and long(ten and fourteen days)soaks.Irrespective of twine material or soak time,all hoop nets entangled the same numbers of giant mud crabs,Scylla serrata implying catch saturation within two days.Only four other animals were caught(all yellowfin bream,Acanthopagrus australis)and all died.At least some replicates of all hoop nets were damaged and lost twine,but this was greatest among the multifilament(up to a maximum of 9.3m hoop-net deployment−1),followed by the multi-monofilament(up to 7.4m hoop-net deployment−1)and monofilament hoop nets(1.4m hoop-net deployment−1).Replacing the existing multifilament twine in hoop nets with monofilament when targeting S.serrata would maintain catches and minimise marine debris during conventional soaks,without increasing ghost fishing over the short term.展开更多
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
Tickler chains are simple additions to the ground gears of benthic trawls that can improve the catches of some target species,albeit with considerable variability.The purpose of this study was to decipher some of the ...Tickler chains are simple additions to the ground gears of benthic trawls that can improve the catches of some target species,albeit with considerable variability.The purpose of this study was to decipher some of the technical variability associated with tickler chains used with generic,paired trawls targeting school prawns,Metapenaeus macleayi.In the first of two experiments,single tickler chains were either attached between the trawl otter boards or the wing ends and compared against each other and a control trawl(no tickler chain).Attaching the tickler chain to the otter boards significantly reduced wing-end spread and the trawled area without significantly affecting catches of school prawns.By comparison,attaching the tickler chain to the wing ends maintained spread and resulted in significantly more school prawns being caught(by 1.11×)than in the control trawl,and also fewer numbers of one teleost species,pink-breasted siphonfish,Siphamia roseigaster.In experiment two,a single tickler chain was compared against one with multiple chains and one with a double chain;all attached at the wing ends.Trawls with the multiple-and double-tickler chains had the same wing-end spread as those with the single tickler chain,while retaining up to 1.17×more school prawns,and for the double-chain tickler,45%fewer southern herring,Herklotsichthys castelnaui.The results are attributed to mechanical and visual stimuli affecting school prawns and some fish,respectively,and support maximising the surface area of tickler chains within the wing ends as a means for improving penaeid-trawl species selectivity without affecting swept area.展开更多
In response to concerns over the mortality of discards and other negative environmental impacts of otter trawling for penaeids,the utility of bottom-set gillnets deployed by artisanal vessels to target Penaeus monodon...In response to concerns over the mortality of discards and other negative environmental impacts of otter trawling for penaeids,the utility of bottom-set gillnets deployed by artisanal vessels to target Penaeus monodon,Metapenaeus affinis and other retained species by-product was assessed in the Sea of Oman.Two gillnets(each comprising several 80-m panels for total lengths of up to 1.3 km)were diurnally fished at two locations(off Beris and Govater,eastern Iran)within established penaeid fishing grounds.During 30 days,the total catch was 2721 kg,comprising penaeids(981 kg),eight retained by-product species(598 kg and mostly Otolithes ruber,Cynoglossus bilinearus and Carangoides talamparoides)and 19 discarded species(1142 kg).The catch-per-unit-of-effort(CPUE,kg/gillnet-panel⋅hour-fished)of targeted penaeids and by-product varied significantly between areas(0.5-1.0 kg),but nevertheless reached economically viable levels.The CPUEs of total bycatch were similar at both sites(<0.5 kg)and no marine turtles were caught.The concomitant ratios of retained-catches-to-bycatch were considerably less than those for regional penaeid-trawl fisheries.Nevertheless,while gillnet selectivity was satisfactory for M.affinis,most of the P.monodon were smaller than their carapace length at maturity at both fished sites.The results support using gillnets to target penaeids and by-product species as an alternative to otter trawling in the Sea of Oman;albeit with ongoing assessments of modifications to maximise selectivity.展开更多
Penaeid trawls often have poor ecological efficiencies measured as unwanted bycatches(with high discard mortality)and<100%effectiveness for all penaeids interacting with the ground gear(with some escape mortality)....Penaeid trawls often have poor ecological efficiencies measured as unwanted bycatches(with high discard mortality)and<100%effectiveness for all penaeids interacting with the ground gear(with some escape mortality).This study investigated the utility of varying ground-chain size(8-vs 10-mm diameter(Ø)stainless-steel chain)and the present or absence of a tickler chain(4-mmØ)for improving efficiencies an Australian fishery diurnally targeting school,Metapenaeus macleayi and eastern king prawns,Penaeus plebejus.There were no treatment effects on wing-end spread and therefore areas trawled.Irrespective of the tickler chain,increasing the ground-chainØreduced catches of total penaeids(by 14%)and jellyfish,Catostylus mosaicus(by 39%)-results speculatively attributed to variation in ground contact and/or a slightly higher footrope in trawls with the 10-mmØchain.By comparison,installing the tickler chain had no effect on eastern king prawns,but increased catches of school prawns(by 1.13×)and bycatches of blue swimmer crabs,Portunus armatus(1.52×;a species with a low discard mortality)and jellyfish(1.23×),while reducing bycatches of two species with high discard mortalities:southern herring,Herklotsichthys castelnaui(by 38%)and squid,Uroteuthis sp.(37%).The results were attributed to the tickler chain producing(1)mechanical stimuli that augmented the capture of benthic-orientated school prawns(but not eastern king prawns owing to diel variations in emergence from the substrata),blue swimmer crabs and jellyfish;and(2)visual stimuli that possibly enabled some southern herring and squid to detect the trawl and escape.The data show tickler chains can improve trawl efficiency for penaeids with at least some positive effects on bycatch that should be rationalised in terms of species-specific vulnerabilities to unaccounted fishing mortality.展开更多
基金funded by the NSW Department of Primary Industriesratified by the NSW Animal Care and Ethics Committee(ACEC ref no.08–06)。
文摘Portunids are important to recreational fisheries in Australia and typically are harvested by baited gears.Most of these baited gears are considered environmentally benign,although small conical hoop(tangle)nets fished in southeastern Australia sometimes are damaged and lose twine,which becomes marine debris.Substituting conventional multifilament polyamide(PA)twine with alternative multi-monofilament and monofilament PA twines in hoop nets can dramatically reduce marine debris,but there remain unanswered questions concerning the relative fishing power of alternative twines among derelict hoop nets.This study addresses the shortfall in data by comparing the efficiencies and damage to replicate hoop nets made from the three twines and left to fish for short(one and two days),medium(three to five days)and long(ten and fourteen days)soaks.Irrespective of twine material or soak time,all hoop nets entangled the same numbers of giant mud crabs,Scylla serrata implying catch saturation within two days.Only four other animals were caught(all yellowfin bream,Acanthopagrus australis)and all died.At least some replicates of all hoop nets were damaged and lost twine,but this was greatest among the multifilament(up to a maximum of 9.3m hoop-net deployment−1),followed by the multi-monofilament(up to 7.4m hoop-net deployment−1)and monofilament hoop nets(1.4m hoop-net deployment−1).Replacing the existing multifilament twine in hoop nets with monofilament when targeting S.serrata would maintain catches and minimise marine debris during conventional soaks,without increasing ghost fishing over the short term.
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.
文摘Tickler chains are simple additions to the ground gears of benthic trawls that can improve the catches of some target species,albeit with considerable variability.The purpose of this study was to decipher some of the technical variability associated with tickler chains used with generic,paired trawls targeting school prawns,Metapenaeus macleayi.In the first of two experiments,single tickler chains were either attached between the trawl otter boards or the wing ends and compared against each other and a control trawl(no tickler chain).Attaching the tickler chain to the otter boards significantly reduced wing-end spread and the trawled area without significantly affecting catches of school prawns.By comparison,attaching the tickler chain to the wing ends maintained spread and resulted in significantly more school prawns being caught(by 1.11×)than in the control trawl,and also fewer numbers of one teleost species,pink-breasted siphonfish,Siphamia roseigaster.In experiment two,a single tickler chain was compared against one with multiple chains and one with a double chain;all attached at the wing ends.Trawls with the multiple-and double-tickler chains had the same wing-end spread as those with the single tickler chain,while retaining up to 1.17×more school prawns,and for the double-chain tickler,45%fewer southern herring,Herklotsichthys castelnaui.The results are attributed to mechanical and visual stimuli affecting school prawns and some fish,respectively,and support maximising the surface area of tickler chains within the wing ends as a means for improving penaeid-trawl species selectivity without affecting swept area.
文摘In response to concerns over the mortality of discards and other negative environmental impacts of otter trawling for penaeids,the utility of bottom-set gillnets deployed by artisanal vessels to target Penaeus monodon,Metapenaeus affinis and other retained species by-product was assessed in the Sea of Oman.Two gillnets(each comprising several 80-m panels for total lengths of up to 1.3 km)were diurnally fished at two locations(off Beris and Govater,eastern Iran)within established penaeid fishing grounds.During 30 days,the total catch was 2721 kg,comprising penaeids(981 kg),eight retained by-product species(598 kg and mostly Otolithes ruber,Cynoglossus bilinearus and Carangoides talamparoides)and 19 discarded species(1142 kg).The catch-per-unit-of-effort(CPUE,kg/gillnet-panel⋅hour-fished)of targeted penaeids and by-product varied significantly between areas(0.5-1.0 kg),but nevertheless reached economically viable levels.The CPUEs of total bycatch were similar at both sites(<0.5 kg)and no marine turtles were caught.The concomitant ratios of retained-catches-to-bycatch were considerably less than those for regional penaeid-trawl fisheries.Nevertheless,while gillnet selectivity was satisfactory for M.affinis,most of the P.monodon were smaller than their carapace length at maturity at both fished sites.The results support using gillnets to target penaeids and by-product species as an alternative to otter trawling in the Sea of Oman;albeit with ongoing assessments of modifications to maximise selectivity.
基金This study was funded by the New South Wales(NSW)Department of Primary Industries
文摘Penaeid trawls often have poor ecological efficiencies measured as unwanted bycatches(with high discard mortality)and<100%effectiveness for all penaeids interacting with the ground gear(with some escape mortality).This study investigated the utility of varying ground-chain size(8-vs 10-mm diameter(Ø)stainless-steel chain)and the present or absence of a tickler chain(4-mmØ)for improving efficiencies an Australian fishery diurnally targeting school,Metapenaeus macleayi and eastern king prawns,Penaeus plebejus.There were no treatment effects on wing-end spread and therefore areas trawled.Irrespective of the tickler chain,increasing the ground-chainØreduced catches of total penaeids(by 14%)and jellyfish,Catostylus mosaicus(by 39%)-results speculatively attributed to variation in ground contact and/or a slightly higher footrope in trawls with the 10-mmØchain.By comparison,installing the tickler chain had no effect on eastern king prawns,but increased catches of school prawns(by 1.13×)and bycatches of blue swimmer crabs,Portunus armatus(1.52×;a species with a low discard mortality)and jellyfish(1.23×),while reducing bycatches of two species with high discard mortalities:southern herring,Herklotsichthys castelnaui(by 38%)and squid,Uroteuthis sp.(37%).The results were attributed to the tickler chain producing(1)mechanical stimuli that augmented the capture of benthic-orientated school prawns(but not eastern king prawns owing to diel variations in emergence from the substrata),blue swimmer crabs and jellyfish;and(2)visual stimuli that possibly enabled some southern herring and squid to detect the trawl and escape.The data show tickler chains can improve trawl efficiency for penaeids with at least some positive effects on bycatch that should be rationalised in terms of species-specific vulnerabilities to unaccounted fishing mortality.
