Dissertationen zum Thema „Fisheries South Australia“

Recent shifts towards ecosystem based fisheries management (EBFM) around the world have necessitated consideration of effects of fishing on a larger range of species than previously. Non-selective multispecies fisheries are particularly problematic for EBFM, as they can contribute to erosion of ecosystem structure. The trade-off between catch of productive commercial species and abundance of low-productivity species is unavoidable in most multispecies fisheries. A first step in evaluation of this trade-off is estimation of productivity of different species but this is often hampered by poor data. This thesis develops techniques for estimating productivity for data-limited species and aims to help clarify EBFM policy objectives for the fisheries of New South Wales (NSW), Australia. It begins with development of an age-structured model parameterised in terms of optimal harvest rate, UMSY. UMSY is a measure of productivity, comparable among species and easily communicated to managers. It also represents a valid threshold for prevention of overfishing. The model is used to derive UMSY for 54 Atlantic fish stocks for which recruitment parameters had previously been estimated. In most cases, UMSY was strongly limited by the age at which fish were first caught. However, for some species, UMSY was more strongly constrained by life history attributes. The model was then applied to twelve species of Australian deepwater dogshark (Order Squaliformes), known to have been severely depleted by fishing. Results showed that the range of possible values of UMSY for these species is very low indeed. These findings enabled a preliminary stock assessment for three dogsharks (Centrophorus spp.) currently being considered for threatened species listing. Preliminary results suggest they have been overfished and that overfishing continues. Finally, an Ecopath with Ecosim ecosystem model, representing the 1976 NSW continental slope, is used to illustrate trade-offs in implementation of fishing policies under alternative policy objectives. Results are compared with those of a biogeochemical ecosystem model (Atlantis) of the same system, built by scientists from CSIRO. While there were large differences in model predictions for individual species, they gave similar results when ranking alternative fishing policies, suggesting that ecosystem models may be useful for exploring broad-scale strategic management options.

Thesis by publication.
Thesis (PhD)--Macquarie University (Division of Environmental & Life Sciences, Graduate School of the Environment), 2007.
Bibliography: p. 267-303.
General introduction -- Redescription of two species of wobbegongs (Chondrichthyes: Orectolobidae) with elevation of Orectolobus halei Whitley 1940 to species level -- Using recreational scuba-divers to survey the relative abundance and distribution of wobbegong sharks (Family: Orectolobidae) in New South Wales, Australia -- Observations of localised movements and residence time of wobbegong sharks (Orectolobus halei) at Fish Rock, New South Wales, Australia -- Length-frequency distribution, length-length, mass-mass and mass-length relationships of wobbegong sharks (Genus Orectolobus) commercially fished in New South Wales, Australia -- Quantitative diet assessment of wobbegong sharks (Genus Orectolobus) in New South Wales, Australia -- Reproductive synchrony of three sympatric species of wobbegong shark (Genus Orectolobus) in New South Wales, Australia -- Age and growth of wobbegong sharks (Genus Orectolobus) in New South Wales, Australia.
In New South Wales, Australia, wobbegong sharks (Orectolobidae) have been commercially targetted by the Ocean Trap and Line Fishery since 1991. A catch decrease of ca. 50% in a decade lead to concern over the sustainability of the fishery and to wobbegongs being listed as vulnerable in NSW under the World Conservation Union Red List assessment. The aim of this research was to investigate wobbegong biology and ecology in relation to its fishery to provide essential data and information for sustainable management of the woggegong fishery. Biological data was obtained from 904 wobbegongs collected from commercial fishing boats, using setlines and lobset pots and by scuba diving. previously two species of wobbegongs were known to occur in NSW: the spotted wobbegong (Orectolobus maculatus) and the ornate wobbegong (O. ornatus). This study discovered a new species (O. halei) described as a subspecies by Whitley (1940), but which had been syonymised with O> ornatus due to a lack of taxonomic investigation.
Mode of access: World Wide Web.
307 p. ill., some col., maps

The Roe’s abalone (Haliotis roei) fishery near Perth, Western Australia, is uniquely accessible, and highly vulnerable to overexploitation. The sustainability of this intensively utilized fishery requires robust assessment. To facilitate an assessment, this research aimed to provide rigorous and detailed biological information with appropriate interpretation. Four critical aspects of the species’ biology and population dynamics were investigated: (1) the stock structure; (2) the recreational catch; (3) an appropriate growth curve and description of size at age; and (4) abundance measures against which to assess the impact of fishing mortality. Allozyme electrophoresis was used to investigate stock structure across the species’ distribution. Standardized variance in allelic frequencies between 10 sites in south-western Australia indicated high levels of gene flow across the 3000 km sampled (mean FST = 0.009). An isolation-by-distance was evident when pairwise measures of GST were related to geographic distance (r=0.45, P<0.001). The area of complete genetic mixing was estimated from samples within the Perth fishery to be less than the distance between the two nearest sites, or 13 km. Consequently, the Perth fishery comprises numerous discrete stocks, each requiring independent assessment. A possible mechanism for this population structure is the retention of larvae in the wind driven currents oscillating in the near-shore lagoons, with rare pulses of long distance dispersal via the southerly Leeuwin current, running further offshore. The presumed impact of intensive recreational fishing, combined with substantial commercial quotas for the Perth fishery, had led to tight restrictions on fishing effort, without any quantitative measure of the recreational catch. A stratified creel survey was adapted to estimate the effort, catch rate and mean weight of abalone harvested by the recreational sector. Catches were estimated for reef complexes, or stocks, of less than 10 nautical miles (18.5 km) of coast. Between 1997 and 2000 the recreational catch varied from 30 to 45 tonnes whole weight, approximately equivalent to the commercial quota of 36 tonnes. On average 88% of the recreational catch came from two stocks, while 98% of the commercial catch came from these two, and one additional, stocks. The incidental mortality from recreational fishing, measured as the number of abalone left dead on the reef as a proportion of the estimated catch, was approximately 7% and 20% at two sites surveyed. Spatial and temporal patterns of growth were examined on the west coast of Western Australia. Growth increments were measured for abalone larger than about 30 mm from tagging studies at five sites in the Perth fishery, a site at the northern extent of the species’ distribution and a site in the southwest. Mean annual growth increments of the 0+ year class were obtained by fitting components to length frequencies from five sites in the Perth fishery, and combined with growth increments from each Perth tag site for model fitting. A von Bertalanffy growth curve provided a slightly better fit to the tag data, but a Gompertz growth curve was a much better fit when the mean increment from the 0+ to 1+ cohort was included, with the inflection occurring at about 40 mm, the size at sexual maturity. There was no difference in annual growth between the two years studied. There was significant variation in growth between the reef platform and adjacent sub-tidal reef, but this variation was site specific and faster growth rates were not consistently associated with either habitat. There was no latitudinal trend in growth rate. Growth at the Perth sites was the fastest and similar at all five sites with growth increments greater in summer than in winter. Size and abundance of abalone were measured using fixed transects and quadrats. Abalone densities were highest on the outer edge of the platform, intermediate in the middle of the reef platform, and lowest on both the inner platform and the sub-tidal reef. The pattern of mean lengths of abalone was the inverse of the density. Mean length and abundance were driven by the presence of post-settlement juveniles on the outer and middle reef habitats. There was a high spatial variation in abundance, with densities varying between transects at the same site, but the trend between years for each transect at a site was not significantly different. Abalone abundances, by size class, were examined from sites sampled between 1996 and 2002. A low density of post-settlement juveniles at all sites in 1997 was reflected in low densities of the 1+ and 2+ year classes in subsequent years. Abalone abundances at an unfished site were steady over the seven years. Two sites were located within each of the main stocks utilised by the recreational fishery. Abundance was stable or increasing in one stock, corresponding to a stable total catch. In the second stock the total catch increased over time and abundances declined. Perth is the focus of the Roe’s abalone fishery, with recreational and commercial fishers take about equal shares of the annual catch. Stocks are highly subdivided, with most of this catch coming from only 3 stocks occupying about 20 nautical miles of coast. Growth rates were found to be lower than previous estimates, and more similar to other commercial species of abalone. All life history stages are highly habitat specific, particularly the recruits, and the distribution and abundance through time indicate that the main stocks are near, or slightly over, the limit of sustainable fishing.

Assessment of trophic interactions between increasing populations of New Zealand fur seals (Arctocephalus forsteri) and fisheries in southern Australia is limited due to a lack of species specific demographic data and an understanding of the factors influencing population growth. To establish species specific demographic parameters a cross-sectional sample of New Zealand fur seal females (330) and males (100) were caught and individually-marked on Kangaroo Island, South Australia between 2000 and 2003. The seals were aged through examination of a postcanine tooth, which was removed from each animal to investigate age-specific life-history parameters. Annual formation of cementum layers was confirmed and accuracy in age estimation was determined by examination of teeth removed from individuals of known-age. Indirect methods of assessing reproductive maturity based on mammary teat characteristics indicated that females first gave birth between 4-8 years of age, with an average age at reproductive maturity of 5 years. Among reproductively mature females, age-specific reproductive rates increased rapidly between 4-7 years of age, reaching maximum rates of 70-81% between 8-13 years, and gradually decreased in older females. No females older than 22 years were recorded to pup. Age of first territory tenure in males ranged from 8-10 years. The oldest female and male were 25 and 19 years old, respectively. Post-weaning growth in females was monophasic, characterised by high growth rates in length and mass during the juvenile growth stage, followed by a gradual decline in growth rates after reproductive maturity. In contrast, growth in males was biphasic and displayed a secondary growth spurt in both length and mass, which coincided with sexual and social maturation, followed by a rapid decline in growth rates. Age-specific survival rates were high (0.823-0.953) among prime-age females (8-13 yrs of age) and declined in older females. Relative change in annual pup production was strongly correlated with reproductive rates of prime-age females and adult female survival between breeding seasons.

Thesis (M.Mar.Archaeol.) -- Flinders University, Department of Archaeology, 2006.
"A thesis submitted in partial fulfilment of the requirements for the degree of Master of Maritime Archaeology, Department of Archaeology, Flinders University". "May 2006". Includes bibliographical references (leaves 101-105). System requirements for remote version: Adobe Acrobat Reader to view PDF file.

Bibliography: leaves 102-106. "The study investigates South Australian (SA) commercial fisheries and aquaculture operations and seal interactions by exploring perceptions in the commercial fishing industry and comparing them to 2nd Century fishers experiences. The results confirm that SA commercial fishers do interact with seals and that interactins with Australian Sea Lions may be disproportionately more than with New Zealand Fur Seals. While some commercial fishers experience is similar to 2nd Century fishers and consider interference by seals to be major hindrance and suggest culling for management of seals, in general, SA commercial fishers are open to mitigation initiatives including gear modifications, to address seal interactions. The dissertation also examines some management mitigation options to minimizing fisheries-seal interactions and offers recommendations." -- ABSTRACT

Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, Discipline of Environmental Biology, 2006.
"January 2006" Bibliography: pages 188-209. Also available in print form.

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.