Assessment of ecological risks from effects of fishing to Piked Spurdog ( Squalus megalops ) in South - Eastern Australia

Target species in some Australian shark fisheries are adequately managed, but there has been little attention given to non - target shark species and there is limited information on the biology of their local populations. Among this group of non-target species, the piked spurdog - Squalus megalops ) is of special interest because it is a dominant and ecologically important species with high natural abundance. Hence, the main purpose of the present research was to improve knowledge of the basic biology of this species and to provide essential data for its management, sustainable use and conservation. Squalus megalops had a complex population structure, segregating by sex, size and breeding condition. The sex ratio was biased towards females and there was sexual size dimorphism with females attaining a larger maximum size than males. Conversion factors from partial lengths to total length and from partial masses to total mass were determined due to the common commercial fishing practice of eviscerating, beheading and finning sharks. Comparisons of total and partial length - length and mass - length relationships between males and females using different ranges of size showed that there was no effect of size range on measurements reflecting only somatic growth ( fork and carcass lengths ; carcass, pectoral fin and caudal fin masses ). However, for variables reflecting somatic and reproductive growth ( total and liver masses ), different outcomes can be expected when different ranges of size are compared. Examination of dietary composition revealed that S. megalops is an opportunistic predator that consumes a wide range of prey items. High variability was found when overall importance of prey items was estimated. Dietary composition varied in space and time, exhibiting differences among regions, seasons and size classes. Therefore, the intrinsic natural variability in the dietary composition of S. megalops and its spatial and temporal variation in diet suggest that information on the ecological relationships among species is likely to be missed when predator - prey interactions are only inferred from overall diet. Reproductive parameters were determined for population assessment. For both sexes, length - at - maturity differed depending on the criterion adopted for defining maturity. Mature males are capable of mating throughout the year. Females have a continuous asynchronous reproductive cycle. The sex ratio of embryos is 1 : 1 and litter size and nearterm embryo size increase with maternal length. Females have an ovarian cycle and gestation period of two years. Although all females are mature at 600 mm, only 50 % of them are in maternal condition, contributing to annual recruitment each year. Hence, for chondrichthyan species with reproductive cycles of two, three or more years, if maturity ogives are used in population assessments instead of maternity ogives, the models will over - estimate recruitment rates. Age and growth information was also determined for population assessment. Precision estimates, the relationship between spine total length and body length, edge analysis, and agreement between counts on the inner dentine layer and the enameled surface support the use of the first dorsal fin spine for the age estimation of S. megalops. Based on goodness - of - fit criterion, the best growth model for males and females was a two - phase von Bertalanffy function. However, model selection cannot be based on quality of statistical fit only and results should be interpreted with caution. Regardless of the model used, the growth rate of S. megalops, particularly of females, is very low, even within the range of growth rates reported for shark species. A three - levelled hierarchical risk assessment approach was trialed to evaluate the suitability of the approach for S. megalops. Integration of qualitative, semi - quantitative, and quantitative biological and fishing impact data showed that S. megalops is potentially highly susceptible to the effects of fishing. A qualitative assessment indicated that the only fishing related activities to have moderate or high impact on S. megalops were those associated with ' capture fishing ' of the otter trawl, Danish seine, gillnet and automatic longline methods. A semi - quantitative assessment ranked S. megalops at risk because of its low biological productivity and, possibly, its catch susceptibility from cumulative effects across the separate fishing methods. Finally, a quantitative assessment showed that population growth is slow even under the assumption of density - dependent compensation where the fishing mortality rate equals the natural mortality rate. Therefore, conservation and management for sustainable use of S. megalops will require a close control of fishing mortality due to the low capacity of this species to withstand fishing pressure.Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2006

Temporal and sexual effects in the feeding ecology of the marbled sand skate Psammobatis bergi Marini, 1932

The definitive version can be found at www.springerlink.com(c) SpringerTemporal and sexual effects in feeding ecology were examined in the marbled sand skate (Psammobatis bergi). Of 137 stomachs analysed, 130 (95%) contained food. Among these, >50% contained between 2 and 4 items, with a maximum of 18 prey items found. Thirty taxonomic levels of prey items were identified: 18 crustaceans, 5 polychaetes, 3 molluscs, 3 teleosts, and 1 chondrichthyan. Coenophthalmus tridentatus and unidentified Brachyura were the dominant prey items by number, frequency of occurrence and index of relative importance (IRI). Libinia spinosa was the dominant item by mass and third most important by %IRI. Psammobatis bergi consumed mostly brachyurans and showed little variability in overall mean prey importance, hence, only a small number of stomachs was needed for a precise description of its dietary composition. There was no interaction between season and sex in the diet composition of P. bergi and there were no differences between the diets of males and females during winter and spring. However, a seasonal pattern was found. The most important prey in spring was C. tridentatus by number and L. spinosa by mass whereas in winter the most important prey was Peltarion spinosulum. The temporal pattern indicates that P. bergi probably modifies its diet in response to prey abundance.M. J. San Martin, J. M. Braccini, L. L. Tamini, G. E. Chiaramonte and J. E. Pere

Frequency of multiple paternity in gummy shark, Mustelus antarcticus, and rig, Mustelus lenticulatus, and the implications of mate encounter rate, postcopulatory influences, and reproductive mode

Elasmobranchs (sharks and rays) show an amazing diversity of reproductive modes and behaviors. Multiple paternity (MP) has been identified in all species where more than 1 litter has been investigated; yet neither direct nor indirect benefits from MP have been determined in elasmobranchs. This has led to the suggestion that MP in this group may simply be a product of convenience polyandry with variation in the frequency of MP driven by differences in mate encounter rates. Here, we use molecular markers to investigate polyandry and MP in 2 closely related and commercially important species of shark, Mustelus antarcticus and Mustelus lenticulatus. In total, 328 M. antarcticus embryos originating from 29 different mothers and 75 M. lenticulatus embryos originating from 19 different mothers were genotyped using 8 microsatellite loci. We find that MP occurs in both species. However, in both species, the majority of litters were sired by a single father. Our results do not support increased fecundity per se as a driver of MP. Further, our results do not suggest that high population densities with resulting high mate encounter rates generated by breeding aggregations necessarily lead to high frequencies of MP. Importantly, we note evidence of reproductive skew within polyandrous litters, which is a predicted outcome of postcopulatory mechanisms.9 page(s

Ecological vulnerability of the chondrichthyan fauna of southern Australia to the stressors of climate change, fishing and other anthropogenic hazards

We develop a potentially widely applicable framework for analysing the vulnerability, resilience risk and exposure of chondrichthyan species to all types of anthropogenic stressors in the marine environment. The approach combines the three components of widely applied vulnerability analysis (exposure, sensitivity and adaptability) (ESA) with three components (exposure, susceptibility and productivity) (ESP) of our adaptation of productivity–susceptibility analysis (PSA). We apply our 12-step ESA‒ESP analysis to evaluate the vulnerability (risk of a marked reduction of the population) of each of 132 chondrichthyan species in the Exclusive Economic Zone of southern Australia. The vul nerability relates to a species’ resilience to a spatial (or suitability) reduction of its habitats from exposure to up to eight climate change stressors. Vulnerability also relates to anthro pogenic mortality added to natural mortality from exposure to the stressors of five types of fishing and seven other types of anthropogenic hazards. We use biological attributes as risk factors to evaluate risk related to resilience at the species or higher taxonomic level. We evaluate each species’ exposure to anthropogenic stressors by assigning it to one of six ecological groups based on its lifestyle (demersal versus pelagic) and habitat, defined by bathymetric range and substrates. We evaluate vulnerability for 11 scenarios: 2000– 2006 when fishing effort peaked; 2018 following a decade of fisheries management reforms; low, medium and high standard future carbon dioxide equivalent emissions sce narios; and their six possible climate–fishing combinations. Our results demonstrate the value of refugia from fishing and how climate change exacerbates the risks from fishing.Fil: Walker, Terence I.. Monash University; Australia. The University of Melbourne; AustraliaFil: Day, Robert W.. The University of Melbourne; AustraliaFil: Awruch, Cynthia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Tasmania; AustraliaFil: Bell, Justin D.. Institute For Marine And Antarctic Studies; AustraliaFil: Braccini, Juan Matias. Wa Fisheries And Marine Research Laboratories; AustraliaFil: Dapp, Derek R.. Monash University; AustraliaFil: Finotto, Licia. Monash University; AustraliaFil: Frick, Lorenz H.. Monash University; AustraliaFil: Garcés-García, Karla C.. Universidad Veracruzana; México. The University of Melbourne; AustraliaFil: Guida, Leonardo. Monash University; AustraliaFil: Huveneers, Charlie. Flinders University; AustraliaFil: Martins, Camila L.. Monash University; AustraliaFil: Rochowski, Bastien E.A.. The University of Melbourne; AustraliaFil: Tovar-Ávila, Javier. Inapesca; MéxicoFil: Trinnie, Fabian I.. Wa Fisheries And Marine Research Laboratories; AustraliaFil: Reina, Richard D.. Monash University; Australi

Evidence of historical isolation and genetic structuring among broadnose sevengill sharks (Notorynchus cepedianus) from the world’s major oceanic regions

Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the broadnose sevengill shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among broadnose sevengill shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions (ΦST = 0.9789, P < 0.0001) and a lack of genetic structuring within regions (ΦST = − 0.007; P = 0.479). Time calibrated Bayesian Inference phylogenetic reconstructions indicate that the observed patterns of genetic structure among oceanic regions are historical, with regional populations estimated to have diverged from a common ancestor during the early to mid-Pleistocene. Our results indicate significant genetic structuring and a lack of gene flow among broadnose sevengill shark populations from the South Atlantic, Oceania and Eastern Pacific regions. Evidence of deep lineage divergences coinciding with the early to mid-Pleistocene suggests historical glacial cycling has contributed to the vicariant divergence of broadnose sevengill shark populations from different ocean basins. These finding will help inform global management of broadnose sevengill shark populations, and provides new insights into historical and contemporary evolutionary processes shaping populations of this ecologically important apex predator

Evidence of historical isolation and genetic structuring among broadnose sevengill sharks (Notorynchus cepedianus) from the world’s major oceanic regions

Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the broadnose sevengill shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among broadnose sevengill shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions (ΦST = 0.9789, P \u3c 0.0001) and a lack of genetic structuring within regions (ΦST = − 0.007; P = 0.479). Time calibrated Bayesian Inference phylogenetic reconstructions indicate that the observed patterns of genetic structure among oceanic regions are historical, with regional populations estimated to have diverged from a common ancestor during the early to mid-Pleistocene. Our results indicate significant genetic structuring and a lack of gene flow among broadnose sevengill shark populations from the South Atlantic, Oceania and Eastern Pacific regions. Evidence of deep lineage divergences coinciding with the early to mid-Pleistocene suggests historical glacial cycling has contributed to the vicariant divergence of broadnose sevengill shark populations from different ocean basins. These finding will help inform global management of broadnose sevengill shark populations, and provides new insights into historical and contemporary evolutionary processes shaping populations of this ecologically important apex predator