The biology and ecology of the blacktip reef shark Carcharhinus melanopterus (Quoy & Gaimard, 1824) and implications for management

[Extract] This project aimed to provide new information on the biology and ecology of the blacktip reef shark to address key knowledge gaps and provide information that informs the conservation and management of the blacktip reef shark. This thesis uses a vulnerability assessment approach that has been applied in a variety of fisheries and natural resource management contexts. This approach has been taken because vulnerability assessments provide a useful framework for organising and integrating different types of information. Vulnerability frameworks have been used to assess a variety of fisheries related risks including the risks to bycatch species such as sea snakes and turtles (Griffiths et al., 2006, Milton, 2001) and sharks and rays (Stobutzki et al., 2002); the economic risks climate change poses to fisheries (Fletcher, 2005); sustainability and risks of targeted fishing for sharks and rays (Salini et al., 2007, Walker, 2005a), and a wide range of other fisheries (see Hobday et al., 2007 for review). Australian fisheries have used vulnerability frameworks which compare a species’ susceptibility to the fishery against its productivity to describe sustainability (Gribble et al., 2005, Hobday et al., 2007, Salini et al., 2007, Stobutzki et al., 2001). Vulnerability frameworks are also used in assessing the vulnerability of species and systems to climate change (Chin et al., 2010, Fussel & Klein, 2006, Johnson & Marshall, 2007). In spite of the diversity of approaches, most vulnerability frameworks used to describe human-environment systems contain common conceptual elements (Adger, 2006): the exposure of the assessment entity (e.g. a species) to risk factors; the sensitivity of the assessment entity to the risks identified; and the adaptive capacity of the species to cope with the risk factors (Adger, 2006). These three components (or 'dimensions') and their interactions describe the characteristics of the entity being assessed, the relationships between these characteristics and external factors, and integrate this information to estimate relative risk (Polsky et al., 2007) (see Fig 1.1). In this project, a vulnerability framework is used to identify and contextualize information about the biology, life history and spatial ecology of the blacktip reef shark, to describe the species' exposure to pressures from fishing and habitat degradation, and to describe the consequences of these interactions for the conservation and management of the species (Fig 1.1). Based on the previously identified knowledge gaps and the implications of these data for the conservation and management of the species, this project is has four discrete aims, each of which is designed to explore critical aspects of the blacktip reef shark's biology, ecology and conservation. Aim 1 (chapter 2): quantify the catch of blacktip reef sharks in the GBR net fishery and describe trends in catch locations and fate of captured sharks. This will document the interactions between the blacktip reef shark and the largest shark fishery operating in the GBRWHA. This information will describe the exposure of the species to fishing pressure which is currently believed to be the most significant pressure facing sharks and rays in the GBRWHA, and provide preliminary information about the blacktip reef shark's occurrence amongst the various habitats of the GBRWHA. Aim 2 (chapter 3): describe the population characteristics of blacktip reef sharks in the GBRWHA lagoon. The project will describe the structure of blacktip reef shark populations in the coastal and inshore regions of the GBRWHA and identify patterns in sex composition and sexual maturity of individuals in a population. The timing and location of critical life history events (e.g. mating, parturition) will also be identified, and population movements (immigration, emigration, dispersal, site fidelity) will be documents. Collectively, these data will help to determine the exposure and sensitivity of the blacktip reef shark to anthropogenic factors such as fishing and habitat degradation. Aim 3 (chapter 4): describe the biology and life history of the blacktip reef shark. The project will provide the first description of the age and growth parameters of the species, and will also provide regionally relevant and validated life history and reproductive parameters such as reproductive periodicity, litter size and size at maturity data. These data will help to assess the species sensitivity to pressures such as fishing and habitat loss. Aim 4 (chapters 5 and 6): describe the movement and habitat use patterns of the blacktip reef shark in the GBRWHA lagoon. The project will document the species' movement and habitat use patterns at a variety of temporal scales to identify critical habitats and movement corridors. The behavior of the blacktip reef shark will also be examined, and the coverage provided by marine park zoning will also be explored. These data will provide information on the species' exposure to anthropogenic pressures, and sensitivity and adaptive capacity to these pressures. The penultimate chapter of the thesis (chapter 7) will draw these elements together to discuss the significance of these data in advancing scientific understanding of the biology and ecology of the study species and the interactions between coastal habitats and sharks and rays, and through the vulnerability framework, provide a comprehensive account of the vulnerability of this species to fishing and habitat loss.