Continental-Scale Network Reveals Cross-Jurisdictional Movements of Sympatric Sharks With Implications for Assessment and Management

Charlie Huveneers,Chris Dowling,Ian Keay,Rory Mcauley,Yuri Niella,Daniela Waltrick,Victor Peddemors,Paul Butcher,Matias Braccini,Silas Mountford,Michael Drew

doi:10.3389/fmars.2021.697175

Abstract

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.

Highlights

Many marine species undertake extensive oceanic and continental-scale movements, which are influenced by a variety of biological and environmental factors, often related to resource needs (e.g., Block et al, 2011; Espinoza et al, 2016)
We investigated the broad-scale movements and levels of connectivity among bronze whalers and dusky sharks in Australian waters between WA, SA, Victoria (VIC), Tasmania (TAS), NSW, and Queensland (QLD), a spatial scale of 7,300 km, using the network of acoustic receivers facilitated through the Integrated Marine Observing System (IMOS) Animal Tracking Facility
We examined the broad-scale movements of dusky sharks and bronze whalers through acoustic tracking and the multiple acoustic receiver arrays combined through the IMOS Animal Tracking Facility

Summary

Introduction

Many marine species undertake extensive oceanic and continental-scale movements, which are influenced by a variety of biological and environmental factors, often related to resource needs (e.g., Block et al, 2011; Espinoza et al, 2016). In species exhibiting large-scale movements, local or regional management measures may not provide adequate protection if the species is exploited in other regions. These species are more likely to move between different jurisdictions, further complicating management and conservation efforts (Heupel et al, 2015). Defining the extent and occurrence of longrange movements is necessary for a comprehensive understanding of a species’ spatial ecology and, within a resource management context, for determining the extent of connectivity among stocks and ensuring sustainable resource use (Lascelles et al, 2014). There is a need to ensure that stock delineation and connectivity are measured at the same temporal scale at which movements occur, since fisheries management operates at the ecological rather than the evolutionary scale. Results from tracking studies might be more relevant to fisheries management, in determining whether stocks are demographically-independent units that should be managed separately (Lédée et al, 2021)

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