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Roberts D.G.,University of Wollongong | Gray C.A.,University of Wollongong | Gray C.A.,Cronulla Fisheries Research Center | West R.J.,University of Wollongong | Ayre D.J.,University of Wollongong
Molecular Ecology | Year: 2010

Populations of obligately estuarine taxa are potentially small and isolated and may lack genetic variation and display regional differentiation as a result of drift and inbreeding. Hybridization with a wide-ranging marine congener should introduce genetic variation and reduce the effects of inbreeding depression and genetic drift. However, high levels of hybridization can cause demographic and genetic swamping. In southeastern Australia hybridization occurs between obligately estuarine Black bream (Acanthopagrus butcheri) and migratory marine Yellowfin bream (Acanthopagrus australis). Here, we surveyed genetic variation at eight microsatellite loci and the mitochondrial control region of juvenile fish from five coastal lagoons (including temporal replication in two lagoons) (total n = 970) to determine the frequency and persistence of hybridization, and its likely consequence for the estuarine restricted A. butcheri. Of 688 juvenile fish genotyped 95% were either A. australis (347) or hybrids (309); only 5% (32) were A. butcheri. Most hybrids were later generation hybrids or A. butcheri backcrosses, which are likely multi-generational residents within lagoons. Far greater proportions of hybrid juveniles were found within two lagoons that are generally closed to the ocean (>90% hybrid fish within generally closed lagoons vs. 12-27% in permanently or intermittently open lagoons). In both lagoons, this was consistent across multiple cohorts of fish [79-97% hybrid fish (n = 282)]. Hybridization and introgression represent a major threat to the persistence of A. butcheri and have yet to be investigated for large numbers of estuarine taxa. © 2010 Blackwell Publishing Ltd. Source

Ives M.C.,Cronulla Fisheries Research Center | Scandol J.P.,University of Sydney | Greenville J.,University of Sydney
Ecological Modelling | Year: 2013

A bio-economic analysis was conducted for two fisheries using a multi-species size-based meta-population model built using the BIOMAS modelling system. The model was built to represent the prawn fisheries of northern New South Wales, Australia and calibrated against 26 years of catch and effort data from this region. A number of alternative management strategies, including the use of more size selective gear and a cap on total effort, were evaluated for their impact on the sustainability of the fish stocks and the profitability of the fleets as well as their robustness to future biological, climatic and economic uncertainties. Although the differences in management strategies were blurred by the uncertainty incorporated into the model there were still some very interesting high-level insights to be gained from the analysis. The modelled prawn species appear to be much more robust to changes in management strategies and product prices than the fleet profits, suggesting the stocks are less vulnerability to such uncertainties than the fleets that harvest them. We also found larger differences in profitability from changes in product prices than from changes in management strategies, indicating that strategies to protect product prices may be of more importance to the profitability of the fisheries than changes to fishing gear or effort levels. Such results highlight the complexity of multi-species, multi-fleet fisheries and the importance of including all relevant species and fisheries in any management strategy evaluations. This complexity can however sometimes mask simple economic truths, such as the need for strategies to maintain the market price of locally caught seafood products under the increasing pressures of international competition. © 2013 Elsevier B.V. Source

Barnes L.,Cronulla Fisheries Research Center | Bellwood D.R.,James Cook University | Sheaves M.,James Cook University | Tanner J.K.,James Cook University
Marine Biology | Year: 2012

Within the tropics, mangroves and coral reefs represent highly productive biomes. Although these habitats are often within close proximity, the role and importance of mangrove habitats for reef fish species remains unclear. Throughout the Indo-Pacific, reef fish species appear to have few links with estuarine mangrove habitats. In contrast, clear-water non-estuarine mangrove habitats throughout the Caribbean support many reef fish species and may be fundamental for sustaining reef fish populations. But how important are clear-water non-estuarine mangroves for reef fishes within the Indo-Pacific? Using visual surveys during diurnal high tide, the fish assemblages inhabiting clear-water mangrove and adjacent reef habitats of Orpheus Island, Great Barrier Reef, were recorded. Of the 188 species of fishes that were recorded, only 38 were observed to inhabit both habitats. Of these, only eight were observed more than five times within each habitat. These observations provide little indication that the clear-water mangroves are an important habitat for reef fish species. In addition, although based on just a 3-month survey period, we found little evidence to suggest that these areas are important nurseries for reef fish species. The clear-water mangroves of Orpheus Island may, however, provide an additional foraging area for the few reef fish species that were observed to utilize these habitats during high tide. The difference in the importance of clear-water mangroves for reef fishes within this study compared with clear-water mangrove counterparts within the Caribbean is surprising. Although only preliminary, our observations would support suggestions that the patterns reflect the different hydrological characteristics and evolutionary histories of these two biogeographic regions. © 2011 Springer-Verlag. Source

Roberts D.G.,University of Wollongong | Gray C.A.,University of Wollongong | West R.J.,University of Wollongong | West R.J.,Cronulla Fisheries Research Center | Ayre D.J.,University of Wollongong
Marine Ecology Progress Series | Year: 2011

We predict estuaries to be hotspots of hybridisation between migratory marine and estuary-restricted species, although hybridisation rates may vary in space and time, reflecting the dynamic nature of estuaries and potentially widespread but erratic dispersal of marine taxa. Within estuaries, genotype frequencies may reflect past hybridisation events, with genetically intermediate and backcrossed individuals contributing to persistent hybrid swarms. In southeastern Australia, hybridisation has occurred between estuarine black bream Acanthopagrus butcheri and marine yellowfin bream A. australis, but it is unclear whether this reflects a contemporary process. We recently found that, within lakes and lagoons at the southern range limit of A. australis, hybrids were abundant and A. butcheri extremely rare, and surprisingly, we detected hybrids within a small sample of fish from the Gippsland Lakes, an estuary 250 km further south. In the present study, we compare the genotypic composition of the contemporary Gippsland Lakes population of Acanthopagrus spp. with the historical composition revealed by analysis of museum specimens. The genetic makeup of samples varied little over time, with ancestral A. butcheri virtually absent, and most introgressed individuals matching expectation for later-generation hybrids or A. butcheri backcrosses, suggesting that the lakes have supported persistent hybrid swarms. At each sampling time, the samples were genetically diverse, as measured by mean number of alleles per locus, which ranged from 8.2 to 9.2, and expected heterozygosity (He), which ranged from 0.66 to 0.70; however, we detected little allelic differentiation (FST= 0.003) across sampling times. Our data imply that introgressed populations of Acanthopagrus spp. are more widespread and persistent than previously predicted. © Inter-Research 2011. Source

Ochwada-Doyle F.,University of New South Wales | Ochwada-Doyle F.,Sydney Institute of Marine Science | Gray C.A.,Cronulla Fisheries Research Center | Loneragan N.R.,Murdoch University | And 2 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2010

Marine stock enhancement is often characterized by poor survival of hatchery-reared individuals due to deficiencies in their fitness, such as a diminished capacity to avoid predators. Field experiments were used to examine predation on Penaeus plebejus, a current candidate for stock enhancement in Australia. We compared overall survival of, and rates of predation on, wild P. plebejus juveniles, naïve hatchery-reared juveniles (which represented the state of individuals intended for stock enhancement) and experienced hatchery-reared juveniles (which had been exposed to natural predatory stimuli). Predation was examined in the presence of an ambush predator (Centropogon australis White, 1790) and an active-pursuit predator (Metapenaeus macleayi Haswell) within both complex (artificial macrophyte) and simple (bare sand and mud) habitats. Overall survival was lower and rates of predation were higher in simple habitats compared to complex habitats in the presence of C. australis. However, the three categories of juveniles survived at similar proportions and suffered similar rates of predation within each individual habitat. No differences in survival and rates of predation were detected among habitats or the categories of juveniles when M. macleayi was used as a predator. These results indicate that wild and hatchery-reared P. plebejus juveniles are equally capable of avoiding predators. Furthermore, exposure of hatchery-reared juveniles to wild conditions does not increase their ability to avoid predators, suggesting an innate rather than learned anti-predator response. The lower predation by C. australis in complex habitats was attributed to a reduction in this ambush predator's foraging efficiency due to the presence of structure. Ecological experiments comparing wild and hatchery-reared individuals should precede all stock enhancement programs because they may identify deficits in hatchery-reared animals that could be mitigated to optimize survival. Such studies can also identify weaknesses in wild animals, relative to hatchery-reared individuals, that may lead to the loss of resident populations. © 2010 Elsevier B.V. All rights reserved. Source

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