This study assessed variability in the length and age compositions, longevity, length-at-age and ... more This study assessed variability in the length and age compositions, longevity, length-at-age and rates of growth and mortality of the east Australian stout whiting Sillago robusta Stead, 1908 population harvested by demersal trawl fisheries. Sampling was done over 2 years and was spatially stratified across three depth strata between 11 and 90 m at two locations approximately 400 km apart. There were no consistent depth-related differences in length and age compositions, but the mean and median length and age of the population was greater at the lower latitude location. Age classes 2 and 3 years dominated samples in the north, and 1 and 2 years in the south. Observed longevity was 10 years in the north, and 6 years in the south. Mean length-at-age was not consistently different between sexes, years or locations, nor did the von Bertalanffy growth function differ significantly between sexes, even though females had a greater estimated L ∞ (23.45 cm FL) compared to males (22.36 cm FL). Estimated natural mortality (M) ranged between 0.42 and 0.77, using age-and length-based methods. Age-based catch-curve analyses identified the instantaneous rate of total mortality (Z) to range between 1.48 and 2.70, with subsequent estimates of fishing mortality (F) ranging between 1.15 and 2.00, being greater than M. Exploitation rates (E) were greater than 0.7, indicating that S. robusta at the study locations was heavily fished. The data provided here can be used as a basis to evaluate future fishery-and climate-related changes in the population demographics of east Australian S. robusta.
The grey nurse shark Carcharias taurus is critically endangered in eastern Australia. Although fu... more The grey nurse shark Carcharias taurus is critically endangered in eastern Australia. Although fully protected, instances of recreational hooking persist in this population, with potentially fatal consequences. Here we used in situ underwater video to quantify the rates at which C. taurus interacts with a range of proximately deployed recreational fishing gears, and we suggest appropriate management changes to limit such interactions. Bottom-set baits elicited strong responses, with 15 to 43% of whole and filleted mackerel baits depredated within 5 min. Smaller Australian sardine (pilchard) and squid baits were taken by C. taurus at a significantly lower, yet appreciable rate of 3 to 15%. These smaller baits were depredated more by recreationally important teleosts, although this relationship was not significant for sardine baits. There was no consistent diel influence on shark bait depredation, although C. taurus was the only nocturnal bait depredator. Trolled gears posed no direct threat to C. taurus at any time, even when trolled at depth. Benthic-oriented jigs were rarely snapped at by C. taurus, yet may still pose a foul-hooking risk as sharks showed a propensity to rub against these jigs at depth. Vertical jigs elicited little response by C. taurus, although foul-hooking was also a risk as jigs contacted sharks in 5% of proximate drops, with near misses or line-only interactions occurring in a further 6% of cases. Our findings suggest that restricting bottom-set baits and benthic-oriented gears such as jigs around C. taurus aggregations would be a feasible and enforceable strategy to minimise recreational fishing interactions.
Variability at small temporal scales can confound comparisons over longer periods of time but has... more Variability at small temporal scales can confound comparisons over longer periods of time but has often been ignored in studies of marine organisms. To determine appropriate methods for sampling fish at multiple temporal scales, we used hierarchical sampling to test hypotheses about temporal and spatial variation of individual species and assemblages of fish sampled with multi-mesh gillnets in shallow and deep habitats of a coastal lake in New South Wales, Australia. The design included temporal scales of 1 wk, 1 and 3 mo and spatial scales of sites (separated by 1 km) and zones (separated by several km). Patterns of temporal variation in univariate and multivariate analyses were complex and inconsistent across the different spatial scales and between habitats. The only general pattern was that spatial variance among replicate gillnet samples in each site was larger than variance at any of the temporal scales examined. Potential mechanisms explaining the observed patterns are likely to be complex and these are considered along with the implications for sampling assemblages of fish. A lack of generality in patterns of temporal variance reinforces the need for pilot studies to identify relevant scales of variation before commencing large-scale, long-term studies of any organism.
2008. Developing a beam trawl for sampling estuarine fish and crustaceans: assessment of a codend... more 2008. Developing a beam trawl for sampling estuarine fish and crustaceans: assessment of a codend cover and effects of different sizes of mesh in the body and codend. -ICES Journal of Marine Science, 65: 687 -696.
North American Journal of Fisheries Management, 2013
In response to experimental evidence and anecdotal concern about bycatch in the net-covered traps... more In response to experimental evidence and anecdotal concern about bycatch in the net-covered traps used increasingly by recreational and commercial fishers to target giant mud crabs Scylla serrata in New South Wales, Australia, experiments were done to examine the utility of escape gaps in reducing the bycatch of Yellowfin Bream Acanthopagrus australis (also known as Surf Bream) and undersized giant mud crabs. In each of two rivers, 10 different treatments comprising four different sizes of rectangular, horizontal escape gaps (85 × 45 mm, 85 × 55 mm, 95 × 45 mm, and 95 × 55 mm) and a control (no escape gaps) applied to both two-entrance and four-entrance traps were tested separately during the day and night. Traps fitted with escape gaps reduced the mean numbers of Yellowfin Bream and undersized giant mud crabs by 53-78% and 58-84%, respectively. Despite some inconsistent results, the effect of escape gaps was statistically significant in four of the seven analyses. There were, however, no significant differences in the mean numbers of Yellowfin Bream and undersized giant mud crabs among the different sizes of escape gap. By contrast, the largest escape gap treatment (i.e., 95 × 55 mm) reduced the mean number of legal-size giant mud crabs by 35-41%, which was significant in one of four analyses. Moreover, size-selectivity analyses indicated that the largest escape gap also allowed a comparatively greater proportion of undersized mud crabs to escape. Our findings show that implementing an 85-mm × 55-mm escape gap could substantially reduce bycatch without affecting catches of the target organism. Further reductions in catches of undersized giant mud crabs is possible with the 95-mm × 55-mm treatment, but at the cost of some reduction in the catch target.
The distribution, recruitment, relative abundance and growth of juvenile mulloway, Argyrosomus ho... more The distribution, recruitment, relative abundance and growth of juvenile mulloway, Argyrosomus hololepidotus LacCpBde, was investigated in the Hawkesbury River. Otter trawling was used monthly between July 1986 and March 1988 at 12 sites along a salinity gradient over 85 km of the estuary. The greatest numbers of juveniles were caught at sites in the mid section of the estuary (20-40 km from the mouth) where salinities were greatly reduced. No A. hololepidotus were caught at sites that were permanently fresh water and few were caught at the marine-dominated sites closest to the mouth of the estuary. The greatest numbers of juveniles were caught between March and September (autumn-winter) and the fewest between October and January (spring-summer). Juveniles with an estimated age of 2-6 months were caught between February and July (late summer-winter) each year at a size of 30-150 mm total length. Juveniles increased in length by 80-100 mm between March and October.
The effects of species of seagrass (Zostera capricorni and Posidonia australis) on spatial and te... more The effects of species of seagrass (Zostera capricorni and Posidonia australis) on spatial and temporal heterogeneity in the demography of estuarine populations of the palaemonid prawn Macrobrachium intermedium across 65 km of the Sydney region, southeastern Australia, were examined. Three estuaries were sampled in 1983 and 1984 to assess the magnitude of intra-and interestuary variability in demographic characteristics among populations. Species of seagrass had no effect on the demographic patterns of populations: differences in the magnitude and directions of change in abundances, recruitment, reproductive characteristics, size structures and growth were as great among populations within each species of seagrass as those between the 2 seagrasses Abiotic factors, such as the location of a meadow in relation to depth of water and distance offshore, and the interactions of these factors with recruiting larvae are hypothesised to have greater influence than the species of seagrass in determining the distribution and abundance of these prawns. Spatial and temporal heterogeneity in demography was similar across all spatial scales sampled: among meadows (50 m to 3 km apart) in a n estuary and among meadows in all 3 estuaries (10 to 65 km apart). Variability in demographic processes among populations in the Sydney region was most likely due to stochastic factors extrinsic to the seagrasses then~selves. I conclude that the demography of seagrass-dwelling estuarine populations of M. lntermedium is basically the same throughout the Sydney region, but differs to that of populations of M. intermedium in seagrasses occurring a t higher latitudes in southeastern Australia. This study emphasises the need to consider spatial and temporal heterogeneity in the demographic processes of a species over various scales to assess the magnitude of flexibility in its life history throughout its distribution.
Under controlled conditions, juvenile eastern lung prawns Penaeus plebejus (Hess) (17 to 27 mm ca... more Under controlled conditions, juvenile eastern lung prawns Penaeus plebejus (Hess) (17 to 27 mm carapace length, CL) tagged with small streamer tags (80 mm long by 2 mm wide) displayed less apparent mortality (proportion of tagged prawns that either died or shed their tag) than those tagged with large streamer tags (90 mm long by 3 mm wide). There were no significant differences in taginduced mortality or tag shedding among tag treatments. The proportion of untagged (control) prawns that died was significantly less than that of prawns tagged with either size of streamer tag. During the 60 d experiment, apparent mortality was greatest over the first 5 and 6 d for small and large tags respectively. At the end of the experiment, mean apparent mortality was 2, 52 and 65 % for controls, small and large tags respectively. Shedding of tags contributed 14 and 19 % to the apparent mortality of prawns tagged with the small or large tags respectively. Growth increments of prawns surviving to the end of the experiment did not differ between prawns tagged with large or small tags, but did differ between sexes (females had a bigger increase in CL than males). Streamer tags of the sizes tested were considered unsuitable for tagging eastern king prawns of 17 to 27 mm CL.
Observer-based estimates of the catches and by-catches from prawn seining (locally termed 'sniggi... more Observer-based estimates of the catches and by-catches from prawn seining (locally termed 'snigging') in Tuggerah Lake (NSW, Australia) during the 1998/99 fishing season are presented. Observed catches included three species of penaeid prawns, while observed by-catches contained a total of 49 finfish and 5 invertebrate taxa. The overall by-catch:prawn catch ratio by weight was 0.9:1, and in catching an estimated 20 ± 4 t of prawns the fleet took an estimated total by-catch of 19 ± 2 t throughout the 6-month fishing season. The by-catch included large numbers of small (<15 cm total length) finfish species important in other commercial and recreational fisheries, including Gerres subfasciatus, Rhabdosargus sarba and Acanthopagrus australis, as well as several small demersal species of little economic value. Multivariate analyses indicated that by-catch composition differed between seines taken over shallow seagrass and bare substrata, with catch rates of several species being greater over seagrass. It is recommended that strategies to reduce potential ecological impacts and by-catch in this fishery be investigated, including fixed spatial closures over seagrasses and the development of alternative fishing gears and practices.
Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to invest... more Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to investigate (i) the optimal positioning of behavioural-type by-catch reduction devices (BRDs) involving square-mesh panels; and (ii) the relative performances of two industry-developed square-mesh panels against a composite square-mesh panel developed by scientists. In the first experiment, three codends, each containing one square-mesh panel (located on the tops of the codend at distances of 0.7, 1.2 and 1.6 m anterior to the last row of meshes respectively) significantly reduced the catches of some small fish and total discards compared with a control codend that held no BRD. Rates of reduction significantly increased with proximity of the square-mesh panel to the end of the codend. There was, however, a significant reduction in catches of prawns from the codend containing the square-mesh panel at 0.7 m. Based on these results, the optimal position for these sorts of BRDs was determined to be at 1.2 m anterior to the last row of meshes. In the second experiment, at this position, two codends containing industry-developed plastic and metal square-mesh panels were less effective in excluding by-catch than a codend containing the composite square-mesh panel. The results are discussed in terms of species-specific differences in behavioural responses and swimming ability and the future development and testing of behavioural-type BRDs in penaeid prawn trawls.
Few fishing methods and gears are entirely selective for the targeted species and their sizes, wi... more Few fishing methods and gears are entirely selective for the targeted species and their sizes, with many retaining at least some incidental catches (collectively termed "bycatch"). Of primary concern is the contribution that the mortalities of such bycatches may have on subsequent stocks. While extensive work to develop modifications to fishing gears has facilitated considerable reductions in bycatches over the past 20 years, very few (if any) of the changes made are 100% effective. There remains, therefore, a substantial mortality of discards in many fisheries, particularly those using trawls. To work more comprehensively towards the ultimate goal of achieving perfect selectivity, we propose that, in addition to conventional bycatch reduction strategies, a lateral approach should also be adopted involving completely alternative gears that, because of their design, operation, or both, have selective mechanisms that could be used to address problematic gears.
The Estuary General Fishery in New South Wales, Australia, is the most complex multimethod and mu... more The Estuary General Fishery in New South Wales, Australia, is the most complex multimethod and multispecies fishery in the state. Approximately 700 fishers target a wide range of organisms using a variety of fishing gears in approximately 80 estuaries. The fishery contains several sub-fisheries, including gill-netting, trapping and beach-seining for finfish, seine-, stow-, and trapnetting for prawns and the collection by hand of pipis, cockles, and beachworms. The fishery is subject to much external pressure because of potential impacts of fishing on estuarine ecosystems and conflicts with other resource users over resource allocation. Because of such concerns, a fishery management strategy was developed and an environmental assessment of the fishery undertaken. A scientific assessment program has been developed to test the performance of the fishery-in terms of delivering on conservation measures-over the next 5 years. The program includes observer studies to assess levels of bycatch and discarding, development of alternate fishing gears and practices where necessary, improved stock assessments via fishery-independent surveys, and risk analyses of potential impacts on ecosystems and other regional interacting fisheries.
The effects on catches and bycatches due to increases in mesh size were investigated in a bottom-... more The effects on catches and bycatches due to increases in mesh size were investigated in a bottom-set gillnet fishery for dusky flathead, Platycephalus fuscus in New South Wales, Australia. Sampling was done in 2 coastal lagoons during spring 2001 using a gillnet comprised of replicate panels of (i) the commercially-used mesh size (7.0 cm) and (ii) 3 larger mesh sizes (8.0, 8.9 and 9.5 cm). The targeted dusky flathead and 5 important bycatch species (bream, Acanthopagrus australis, luderick, Girella tri-cuspidata, sea mullet, Mugil cephalus, yellow-finned leatherjacket, Meuschenia trachylepis and blue swimmer crab, Portunus pelagicus) accounted for approx. 91 % of the total catch. Significant differences in the catch rates of these species were detected among the mesh sizes examined with trends for fewer numbers of total dusky flathead, total bycatch, sea mullet, yellow-finned leatherjacket and under-size bream and luderick evident in the larger mesh sizes. All species were character...
This study assessed variability in the length and age compositions, longevity, length-at-age and ... more This study assessed variability in the length and age compositions, longevity, length-at-age and rates of growth and mortality of the east Australian stout whiting Sillago robusta Stead, 1908 population harvested by demersal trawl fisheries. Sampling was done over 2 years and was spatially stratified across three depth strata between 11 and 90 m at two locations approximately 400 km apart. There were no consistent depth-related differences in length and age compositions, but the mean and median length and age of the population was greater at the lower latitude location. Age classes 2 and 3 years dominated samples in the north, and 1 and 2 years in the south. Observed longevity was 10 years in the north, and 6 years in the south. Mean length-at-age was not consistently different between sexes, years or locations, nor did the von Bertalanffy growth function differ significantly between sexes, even though females had a greater estimated L ∞ (23.45 cm FL) compared to males (22.36 cm FL). Estimated natural mortality (M) ranged between 0.42 and 0.77, using age-and length-based methods. Age-based catch-curve analyses identified the instantaneous rate of total mortality (Z) to range between 1.48 and 2.70, with subsequent estimates of fishing mortality (F) ranging between 1.15 and 2.00, being greater than M. Exploitation rates (E) were greater than 0.7, indicating that S. robusta at the study locations was heavily fished. The data provided here can be used as a basis to evaluate future fishery-and climate-related changes in the population demographics of east Australian S. robusta.
The grey nurse shark Carcharias taurus is critically endangered in eastern Australia. Although fu... more The grey nurse shark Carcharias taurus is critically endangered in eastern Australia. Although fully protected, instances of recreational hooking persist in this population, with potentially fatal consequences. Here we used in situ underwater video to quantify the rates at which C. taurus interacts with a range of proximately deployed recreational fishing gears, and we suggest appropriate management changes to limit such interactions. Bottom-set baits elicited strong responses, with 15 to 43% of whole and filleted mackerel baits depredated within 5 min. Smaller Australian sardine (pilchard) and squid baits were taken by C. taurus at a significantly lower, yet appreciable rate of 3 to 15%. These smaller baits were depredated more by recreationally important teleosts, although this relationship was not significant for sardine baits. There was no consistent diel influence on shark bait depredation, although C. taurus was the only nocturnal bait depredator. Trolled gears posed no direct threat to C. taurus at any time, even when trolled at depth. Benthic-oriented jigs were rarely snapped at by C. taurus, yet may still pose a foul-hooking risk as sharks showed a propensity to rub against these jigs at depth. Vertical jigs elicited little response by C. taurus, although foul-hooking was also a risk as jigs contacted sharks in 5% of proximate drops, with near misses or line-only interactions occurring in a further 6% of cases. Our findings suggest that restricting bottom-set baits and benthic-oriented gears such as jigs around C. taurus aggregations would be a feasible and enforceable strategy to minimise recreational fishing interactions.
Variability at small temporal scales can confound comparisons over longer periods of time but has... more Variability at small temporal scales can confound comparisons over longer periods of time but has often been ignored in studies of marine organisms. To determine appropriate methods for sampling fish at multiple temporal scales, we used hierarchical sampling to test hypotheses about temporal and spatial variation of individual species and assemblages of fish sampled with multi-mesh gillnets in shallow and deep habitats of a coastal lake in New South Wales, Australia. The design included temporal scales of 1 wk, 1 and 3 mo and spatial scales of sites (separated by 1 km) and zones (separated by several km). Patterns of temporal variation in univariate and multivariate analyses were complex and inconsistent across the different spatial scales and between habitats. The only general pattern was that spatial variance among replicate gillnet samples in each site was larger than variance at any of the temporal scales examined. Potential mechanisms explaining the observed patterns are likely to be complex and these are considered along with the implications for sampling assemblages of fish. A lack of generality in patterns of temporal variance reinforces the need for pilot studies to identify relevant scales of variation before commencing large-scale, long-term studies of any organism.
2008. Developing a beam trawl for sampling estuarine fish and crustaceans: assessment of a codend... more 2008. Developing a beam trawl for sampling estuarine fish and crustaceans: assessment of a codend cover and effects of different sizes of mesh in the body and codend. -ICES Journal of Marine Science, 65: 687 -696.
North American Journal of Fisheries Management, 2013
In response to experimental evidence and anecdotal concern about bycatch in the net-covered traps... more In response to experimental evidence and anecdotal concern about bycatch in the net-covered traps used increasingly by recreational and commercial fishers to target giant mud crabs Scylla serrata in New South Wales, Australia, experiments were done to examine the utility of escape gaps in reducing the bycatch of Yellowfin Bream Acanthopagrus australis (also known as Surf Bream) and undersized giant mud crabs. In each of two rivers, 10 different treatments comprising four different sizes of rectangular, horizontal escape gaps (85 × 45 mm, 85 × 55 mm, 95 × 45 mm, and 95 × 55 mm) and a control (no escape gaps) applied to both two-entrance and four-entrance traps were tested separately during the day and night. Traps fitted with escape gaps reduced the mean numbers of Yellowfin Bream and undersized giant mud crabs by 53-78% and 58-84%, respectively. Despite some inconsistent results, the effect of escape gaps was statistically significant in four of the seven analyses. There were, however, no significant differences in the mean numbers of Yellowfin Bream and undersized giant mud crabs among the different sizes of escape gap. By contrast, the largest escape gap treatment (i.e., 95 × 55 mm) reduced the mean number of legal-size giant mud crabs by 35-41%, which was significant in one of four analyses. Moreover, size-selectivity analyses indicated that the largest escape gap also allowed a comparatively greater proportion of undersized mud crabs to escape. Our findings show that implementing an 85-mm × 55-mm escape gap could substantially reduce bycatch without affecting catches of the target organism. Further reductions in catches of undersized giant mud crabs is possible with the 95-mm × 55-mm treatment, but at the cost of some reduction in the catch target.
The distribution, recruitment, relative abundance and growth of juvenile mulloway, Argyrosomus ho... more The distribution, recruitment, relative abundance and growth of juvenile mulloway, Argyrosomus hololepidotus LacCpBde, was investigated in the Hawkesbury River. Otter trawling was used monthly between July 1986 and March 1988 at 12 sites along a salinity gradient over 85 km of the estuary. The greatest numbers of juveniles were caught at sites in the mid section of the estuary (20-40 km from the mouth) where salinities were greatly reduced. No A. hololepidotus were caught at sites that were permanently fresh water and few were caught at the marine-dominated sites closest to the mouth of the estuary. The greatest numbers of juveniles were caught between March and September (autumn-winter) and the fewest between October and January (spring-summer). Juveniles with an estimated age of 2-6 months were caught between February and July (late summer-winter) each year at a size of 30-150 mm total length. Juveniles increased in length by 80-100 mm between March and October.
The effects of species of seagrass (Zostera capricorni and Posidonia australis) on spatial and te... more The effects of species of seagrass (Zostera capricorni and Posidonia australis) on spatial and temporal heterogeneity in the demography of estuarine populations of the palaemonid prawn Macrobrachium intermedium across 65 km of the Sydney region, southeastern Australia, were examined. Three estuaries were sampled in 1983 and 1984 to assess the magnitude of intra-and interestuary variability in demographic characteristics among populations. Species of seagrass had no effect on the demographic patterns of populations: differences in the magnitude and directions of change in abundances, recruitment, reproductive characteristics, size structures and growth were as great among populations within each species of seagrass as those between the 2 seagrasses Abiotic factors, such as the location of a meadow in relation to depth of water and distance offshore, and the interactions of these factors with recruiting larvae are hypothesised to have greater influence than the species of seagrass in determining the distribution and abundance of these prawns. Spatial and temporal heterogeneity in demography was similar across all spatial scales sampled: among meadows (50 m to 3 km apart) in a n estuary and among meadows in all 3 estuaries (10 to 65 km apart). Variability in demographic processes among populations in the Sydney region was most likely due to stochastic factors extrinsic to the seagrasses then~selves. I conclude that the demography of seagrass-dwelling estuarine populations of M. lntermedium is basically the same throughout the Sydney region, but differs to that of populations of M. intermedium in seagrasses occurring a t higher latitudes in southeastern Australia. This study emphasises the need to consider spatial and temporal heterogeneity in the demographic processes of a species over various scales to assess the magnitude of flexibility in its life history throughout its distribution.
Under controlled conditions, juvenile eastern lung prawns Penaeus plebejus (Hess) (17 to 27 mm ca... more Under controlled conditions, juvenile eastern lung prawns Penaeus plebejus (Hess) (17 to 27 mm carapace length, CL) tagged with small streamer tags (80 mm long by 2 mm wide) displayed less apparent mortality (proportion of tagged prawns that either died or shed their tag) than those tagged with large streamer tags (90 mm long by 3 mm wide). There were no significant differences in taginduced mortality or tag shedding among tag treatments. The proportion of untagged (control) prawns that died was significantly less than that of prawns tagged with either size of streamer tag. During the 60 d experiment, apparent mortality was greatest over the first 5 and 6 d for small and large tags respectively. At the end of the experiment, mean apparent mortality was 2, 52 and 65 % for controls, small and large tags respectively. Shedding of tags contributed 14 and 19 % to the apparent mortality of prawns tagged with the small or large tags respectively. Growth increments of prawns surviving to the end of the experiment did not differ between prawns tagged with large or small tags, but did differ between sexes (females had a bigger increase in CL than males). Streamer tags of the sizes tested were considered unsuitable for tagging eastern king prawns of 17 to 27 mm CL.
Observer-based estimates of the catches and by-catches from prawn seining (locally termed 'sniggi... more Observer-based estimates of the catches and by-catches from prawn seining (locally termed 'snigging') in Tuggerah Lake (NSW, Australia) during the 1998/99 fishing season are presented. Observed catches included three species of penaeid prawns, while observed by-catches contained a total of 49 finfish and 5 invertebrate taxa. The overall by-catch:prawn catch ratio by weight was 0.9:1, and in catching an estimated 20 ± 4 t of prawns the fleet took an estimated total by-catch of 19 ± 2 t throughout the 6-month fishing season. The by-catch included large numbers of small (<15 cm total length) finfish species important in other commercial and recreational fisheries, including Gerres subfasciatus, Rhabdosargus sarba and Acanthopagrus australis, as well as several small demersal species of little economic value. Multivariate analyses indicated that by-catch composition differed between seines taken over shallow seagrass and bare substrata, with catch rates of several species being greater over seagrass. It is recommended that strategies to reduce potential ecological impacts and by-catch in this fishery be investigated, including fixed spatial closures over seagrasses and the development of alternative fishing gears and practices.
Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to invest... more Two experiments were done in the oceanic penaeid prawn-trawl fishery in New South Wales to investigate (i) the optimal positioning of behavioural-type by-catch reduction devices (BRDs) involving square-mesh panels; and (ii) the relative performances of two industry-developed square-mesh panels against a composite square-mesh panel developed by scientists. In the first experiment, three codends, each containing one square-mesh panel (located on the tops of the codend at distances of 0.7, 1.2 and 1.6 m anterior to the last row of meshes respectively) significantly reduced the catches of some small fish and total discards compared with a control codend that held no BRD. Rates of reduction significantly increased with proximity of the square-mesh panel to the end of the codend. There was, however, a significant reduction in catches of prawns from the codend containing the square-mesh panel at 0.7 m. Based on these results, the optimal position for these sorts of BRDs was determined to be at 1.2 m anterior to the last row of meshes. In the second experiment, at this position, two codends containing industry-developed plastic and metal square-mesh panels were less effective in excluding by-catch than a codend containing the composite square-mesh panel. The results are discussed in terms of species-specific differences in behavioural responses and swimming ability and the future development and testing of behavioural-type BRDs in penaeid prawn trawls.
Few fishing methods and gears are entirely selective for the targeted species and their sizes, wi... more Few fishing methods and gears are entirely selective for the targeted species and their sizes, with many retaining at least some incidental catches (collectively termed "bycatch"). Of primary concern is the contribution that the mortalities of such bycatches may have on subsequent stocks. While extensive work to develop modifications to fishing gears has facilitated considerable reductions in bycatches over the past 20 years, very few (if any) of the changes made are 100% effective. There remains, therefore, a substantial mortality of discards in many fisheries, particularly those using trawls. To work more comprehensively towards the ultimate goal of achieving perfect selectivity, we propose that, in addition to conventional bycatch reduction strategies, a lateral approach should also be adopted involving completely alternative gears that, because of their design, operation, or both, have selective mechanisms that could be used to address problematic gears.
The Estuary General Fishery in New South Wales, Australia, is the most complex multimethod and mu... more The Estuary General Fishery in New South Wales, Australia, is the most complex multimethod and multispecies fishery in the state. Approximately 700 fishers target a wide range of organisms using a variety of fishing gears in approximately 80 estuaries. The fishery contains several sub-fisheries, including gill-netting, trapping and beach-seining for finfish, seine-, stow-, and trapnetting for prawns and the collection by hand of pipis, cockles, and beachworms. The fishery is subject to much external pressure because of potential impacts of fishing on estuarine ecosystems and conflicts with other resource users over resource allocation. Because of such concerns, a fishery management strategy was developed and an environmental assessment of the fishery undertaken. A scientific assessment program has been developed to test the performance of the fishery-in terms of delivering on conservation measures-over the next 5 years. The program includes observer studies to assess levels of bycatch and discarding, development of alternate fishing gears and practices where necessary, improved stock assessments via fishery-independent surveys, and risk analyses of potential impacts on ecosystems and other regional interacting fisheries.
The effects on catches and bycatches due to increases in mesh size were investigated in a bottom-... more The effects on catches and bycatches due to increases in mesh size were investigated in a bottom-set gillnet fishery for dusky flathead, Platycephalus fuscus in New South Wales, Australia. Sampling was done in 2 coastal lagoons during spring 2001 using a gillnet comprised of replicate panels of (i) the commercially-used mesh size (7.0 cm) and (ii) 3 larger mesh sizes (8.0, 8.9 and 9.5 cm). The targeted dusky flathead and 5 important bycatch species (bream, Acanthopagrus australis, luderick, Girella tri-cuspidata, sea mullet, Mugil cephalus, yellow-finned leatherjacket, Meuschenia trachylepis and blue swimmer crab, Portunus pelagicus) accounted for approx. 91 % of the total catch. Significant differences in the catch rates of these species were detected among the mesh sizes examined with trends for fewer numbers of total dusky flathead, total bycatch, sea mullet, yellow-finned leatherjacket and under-size bream and luderick evident in the larger mesh sizes. All species were character...
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