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Large-bodied sharks can be critical for coupling disparate habitats and food webs, which is considered central for ecosystem stability. Understanding the role of sharks and their associated predator–prey relationships across spatial scales is also integral to the development of multi-species ecosystem models. A combined stomach content (n = 212) and multi-tissue stable isotope (fast [liver; n = 101] vs slow turnover [muscle; n = 108]) approach was used to investigate the feeding ecology of the copper shark (Carcharhinus brachyurus) in the temperate waters of Southern Australia. Sharks were sampled from fishery catches over 3 years, during the austral spring–summer seasons and across three distinct regions. Stomach content analysis identified the copper shark as a generalist predator that consumes a diverse prey base dominated by Sepia novaehollandiae, Sepioteuthis australis, and Sardinops sagax (36%, 21%, and 18% IRI). Regional differences in diet composition were evident, although no size- or sex-based variation was identified. Isotope mixing models and regional food web bi-plots also revealed that S. sagax was the most important prey species, but temporal variation in diet was observed that matched known movements. The copper shark was estimated to be a primary piscivore, feeding at trophic level 4.49. Data on the feeding behaviour of copper sharks will provide vital inputs into future ecosystem-based fishery models and guide conservation and management of this important marine predator in temperate Southern Australian coastal waters. [ABSTRACT FROM AUTHOR]

There are increasing concerns over the possible effects of aquaculture pens on the local abundance and residency of sharks, and its associated risk for shark bites at nearby beaches and surf breaks. We used acoustic tracking and a before–during–after–control–impact design to assess the residency and local abundance of 117 bronze whalers and 843 white sharks around a 45-m-diameter aquaculture pen installed in South Australia for tourism purposes. Only 14 bronze whalers (12.0% of individuals tagged) and nine white sharks (1.1% of individuals tagged) were detected throughout the 5-year monitoring period and there was no evidence of the pen affecting these sharks, in either the number of sharks detected or number of detections (proxy for length of time detected). The low amount of interactions with the pen was likely to be due to a combination of low fish biomass, pen installed in a shallow location, local shark species being migratory species, and good husbandry practices. Adequate planning and management, and good husbandry practices, such as removal of dead fish from pens and avoiding over-feeding to ensure the feed is entirely consumed, are key to reducing shark interactions with cage fish and associated infrastructure. Sharks are often observed interacting with caged fish and aquaculture industries. We tracked ∼900 bronze whalers and white sharks to determine whether local shark populations are affected by an aquaculture pen installed for tourism purposes. We found no evidence that sharks were attracted by the pen or stayed in the region for extended periods because of the pen. Good husbandry practices, shallow location, and shark species being migratory likely contributed to the low number of interactions with the pen. [ABSTRACT FROM AUTHOR]

Understanding the movement ecology of marine species and connectivity of populations is required for effective fisheries management. This is especially the case for species with wide-ranging distributions for which movement can span across several jurisdictions with different management regulations. We used the Australian national network of acoustic receivers facilitated by the Integrated Marine Observing System (IMOS) to describe the extent and frequency of movements for two large epipelagic shark species, the bronze whaler (Carcharhinus brachyurus) and dusky shark (Carcharhinus obscurus). A total of 210 sharks (117 bronze whalers and 93 dusky sharks) were tracked for a 10-year period during which 21% and 9% of detected bronze whalers and dusky sharks, respectively, moved between Australian states. Bronze whalers showed more variable inter-state movements, mostly between Western Australia and South Australia but also eastwards to New South Wales (NSW). Although no dusky sharks tagged in Western Australia undertook inter-state movements, ∼50% of the sharks tagged in South Australia went to Western Australia. Five of the 14 dusky sharks tagged in NSW (36%) were detected across different states but remained on the east and southeast coasts (Queensland, NSW, Victoria, and Tasmania). The IMOS receivers also detected six bronze whalers in Ningaloo Reef, representing an extension of the previously known Australian distribution. Our findings highlight the value of collaboration between researchers and the value of national infrastructure, by providing a more accurate understanding of inter-state movements. This new information will allow the development of more adequate population dynamic models for stock assessment and management advice, requiring collaboration among state agencies for coordinating research activities, sharing data and resources, and establishing appropriate cross-jurisdictional policies. This is essential to achieve successful management and conservation outcomes for highly migratory species.

The copper or bronze whaler shark (Carcharhinus brachyurus) is a large, coastal top predator that is vulnerable to overexploitation. We test the null hypothesis that copper sharks are panmictic throughout the southern hemisphere. We analysed part of the mitochondrial control region (mtCR) in 120 individuals from eight sampling areas, defining 20 mtCR haplotypes (h = 0.76 ± 0.06, π = 0.016 ± 0.0007). Significant genetic structure was detected among the following three major coastal regions separated by oceanic habitat: Australia--New Zealand, South Africa--Namibia and Perú (AMOVA ΦST = 0.95, P < 0.000001). A major phylogeographic discontinuity exists across the Indian Ocean, indicating an absence of at least female-mediated gene flow for ~3 million years. We propose that this species originated in the Atlantic, experienced vicariant isolation of Pacific and Atlantic lineages by the rise of the Isthmus of Panama and, subsequently, dispersed across the Pacific to colonise Australasia. Oceanic expanses appear to be traversed over evolutionary but not ecological timescales, which means that regional copper-shark populations should be assessed and managed independently. [ABSTRACT FROM AUTHOR]