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Sharks and other chondrichthyans are often described as long lived, slow growing and producing few offspring. These biological characteristics, together with the common assumption that recruitment is directly related to stock, and pessimistic stock prognoses obtained from application of demographic analysis, have led to doubts that sharks can be harvested sustainably. Developed over the past 40 or so years from studies of only a few shark species, these doubts have been reinforced by declining catch rates in industrial, artisanal and recreational fisheries and in fishing programmes designed to reduce the risk of sharks attacking humans at bathing beaches. However, more recent studies and application of modelling techniques allowing for density-dependent responses to the effects of stock reduction indicate that shark stocks can be harvested sustainably and, if carefully managed, can provide very stable fisheries. It is now understood that some species (such as Galeorhinus galeus, Carcharhinus plumbeus, Carcharodon carcharias and several species of dogfish) have low productivity, whereas other species (such as Mustelus antarcticus, Rhizoprionodon terraenovae, Sphyrna tiburo and Prionace glauca) have higher productivity. This paper reviews the use of shark products, the effects of fishing on shark populations of the world, and recent developments in assessment of shark fishery stocks.

An Integrated Risk Assessment for Climate Change (IRACC) is developed and applied to assess the vulnerability of sharks and rays on Australia's Great Barrier Reef (GBR) to climate change. The IRACC merges a traditional climate change vulnerability framework with approaches from fisheries ecological risk assessments. This semi-quantitative assessment accommodates uncertainty and can be applied at different spatial and temporal scales to identify exposure factors, at-risk species and their key biological and ecological attributes, critical habitats a'nd ecological processes, and major knowledge gaps. Consequently, the IRACC can provide a foundation upon which to develop climate change response strategies. Here, we describe the assessment process, demonstrate its application to GBR shark and ray species, and explore the issues affecting their vulnerability to climate change. The assessment indicates that for the GBR, freshwater/estuarine and reef associated sharks and rays are most vulnerable to climate change, and that vulnerability is driven by case-specific interactions of multiple factors and species attributes. Changes in temperature, freshwater input and ocean circulation will have the most widespread effects on these species. Although relatively few GBR sharks and rays were assessed as highly vulnerable, their vulnerability increases when synergies with other factors are considered. This is especially true for freshwater/estuarine and coastal/inshore sharks and rays. Reducing the impacts of climate change on the GBR's sharks and rays requires a range of approaches including mitigating climate change and addressing habitat degradation and sustainability issues. Species-specific conservation actions may be required for higher risk species (e.g. the freshwater whipray, porcupine ray, speartooth shark and sawfishes) including reducing mortality, preserving coastal catchments and estuarine habitats, and addressing fisheries sustainability. The assessment identified many knowledge gaps concerning GBR habitats and processes, and highlights the need for improved understanding of the biology and ecology of the sharks and rays of the GBR.

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Mustelus antarcticus, endemic to southern Australia, exhibits matrotrophic aplacental viviparity. Differences in synchronous ovarian and parturition cycles, mostly annual west and biennial east of longitude 138°E, are explained by environmental differences. Ovulation and parturition peak during November–December and the gestation period is ~12 months. Largest ovarian follicle diameter ranges from 15 to 28 mm at ovulation, and mean wet mass gain is 10-fold from in utero egg (~10 g) to full-term embryo (~100 g) at ~330 mm total length. The sex ratio of embryos in utero is 1:1, and litter size (1 to 57 embryos) rises curvilinearly with maternal length. Length-at-maternity and length-at-maturity increased with rising fishing mortality and subsequently decreased with falling fishing mortality. These patterns are explained by the hypothesis on the ‘phenomenon of apparent change of size-at-maternity’ (and size-at-maturity) caused by gill-net length-selective fishing mortality, which masks any potential density-dependent responses. Male length-at-maturity estimates from seminal vesicle condition, testis development and spermatogenesis stages are similar, but are less than estimates from clasper calcification. Maximum body mass of females is double that of males and, at any length >700 mm, mean body mass of females exceeds that of males.

Experiments designed to estimate length-specific selectivities for gill nets used to catch gummy shark, M. antarcticus, were carried out in south-eastern Australian waters between 1973 and 1976. Eight nets were used, with mesh sizes ranging from 5.08 to 22.78 cm (2-9 in.) in steps of 2.54 cm (1 in.). Existing methods for estimating mesh selectivities are reviewed, and an alternative method, which overcomes some problems in the existing methods, is described. In this method, an assumed selectivity function is fitted directly to catch data for a number of different mesh sizes, with the parameters of the selectivity function being estimated simultaneously across mesh sizes and length-classes. The new method is used to estimate selectivities for the gummy shark data, on the assumption that the selectivity function takes the shape of a gamma distribution. Data from the 2- and 3-in. mesh nets did not satisfy the assumptions of the procedure, but estimates of mesh selectivities were successfully obtained for the 4-9-in. mesh nets.

Population assessments of chondrichthyan species require several key parameters of their reproductive biology, which were estimated for Squalus megalops (Macleay, 1881). Length-at-maturity differed depending on the criterion adopted for defining maturity. In the case of males, length-at-maturity was smallest when condition of seminal vesicles was adopted as a maturity criterion. For females, length-at-maturity was smallest when the largest follicle diameter >3 mm was adopted as the criterion for maturity; this was appropriate only as an indicator of the onset of 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 near-term embryo length increase with maternal length. Females have an ovarian cycle and gestation period of two years. This was reflected in the differences found between the maturity and maternity ogives. Although all females are mature at 600 mm, only 50% of them contribute 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 overestimate recruitment rates.