Abstract. Small-scale and artisanal fisheries for sharks exist in most inshore, tropical regions of the world. Although often important in terms of food security, their low value and inherent complexity provides an imposing hurdle to sustainable management. An observer survey of a small-scale commercial gill-net fishery operating within the Great Barrier Reef World Heritage area revealed at least 38 species of elasmobranch were present in the catch. Of the total elasmobranch catch, 95% was 25 species of Carcharhiniformes from the families Carcharhinidae, Hemigaleidae and Sphyrnidae. Individual species were captured in a variety of ways by the fishery, often with strongly biased sex ratios and in a variety of life stages (e.g. neonates, juveniles, adult). Despite this, the main carcharhiniform taxa captured could be qualitatively categorised into four groups based on similar catch characteristics, body size and similarities in life history: small coastal (,1000 mm); medium coastal (1000-2000 mm); large coastal/semi-pelagic (.2000 mm); and hammerheads. Such groupings can potentially be useful for simplifying management of complex multispecies fisheries. The idiosyncrasies of elasmobranch populations and how fisheries interact with them provide a challenge for management but, if properly understood, potentially offer underutilised options for designing management strategies.

Interspecies hybridisation in nature is a wellstudied phenomenon, but it has not been analysed using genetic markers in the class Chondrichthyes (sharks, rays and chimeras). Two black-tip whaler shark species (Australian, Carcharhinus tilstoni; Common, C. limbatus) have overlapping distributions in Australia, distinct mitochondrial DNA sequence (ND4, COI, control region) and distinct morphological features such as length at sexual maturity, length at birth and number of vertebrae. A mismatch was observed between species identification using mtDNA sequence and species identification using morphological characters. To test whether hybridisation between the two species was responsible, a nuclear gene with species-specific mutations was sequenced. Extensive interspecies hybridisation was found to be occurring. Hybrids were found from five locations on the eastern Australian coastline, spanning 2,000 km. If hybrid fitness is low and hybrids are common, then fisheries recruitment may be overestimated and the productivity of the black-tip shark fishery may be well below that required to support commercial exploitation. To guard against identification errors, the likelihood of hybridisation and subsequent introgression should be assessed prior to using mtDNA (e.g. barcoding) to identify shark species. The C. limbatus-C. tilstoni species complex provides a unique opportunity to investigate the ability of sharks to adapt to environmental change, in particular, the impact of hybridization on species distributions which favour C. tilstoni along the north and C. limbatus along the south eastern Australian coastline.

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Estimates of life-history parameters were made for shark-like batoids of conservation concern Rhynchobatus spp. (Rhynchobatus australiae, Rhynchobatus laevis and Rhynchobatus palpebratus) and Glaucostegus typus using vertebral ageing. The sigmoid growth functions, Gompertz and logistic, best described the growth of Rhynchobatus spp. and G. typus, providing the best statistical fit and most biologically appropriate parameters. The two-parameter logistic was the preferred model for Rhynchobatus spp. with growth parameter estimates (both sexes combined) L(∞) = 2045 mm stretch total length, LST and k = 0·41 year⁻¹. The same model was also preferred for G. typus with growth parameter estimates (both sexes combined) L∞  = 2770 mm LST and k = 0·30 year⁻¹. Annual growth-band deposition could not be excluded in Rhynchobatus spp. using mark-recaptured individuals. Although morphologically similar G. typus and Rhynchobatus spp. have differing life histories, with G. typus longer lived, slower growing and attaining a larger maximum size.