RESUMEN
Acoustic telemetry has been used to monitor the movement of aquatic animals in a broad range of aquatic environments. Despite their importance, mangrove habitats are understudied for the spatial ecology of elasmobranchs, with acoustic telemetry rarely used inside mangrove habitats. One reason for this may be a general assumption that acoustic signals would not be able to be detected by receivers in such shallow, structurally complex, environments. This study tested whether acoustic receivers can be used inside mangrove habitats to track the movement of sharks and rays. Thirty-eight receivers were deployed in a mangrove system in Pioneer Bay, Orpheus Island, Great Barrier Reef, including inside mangroves, mangrove edges, and adjacent reef flat areas. The detection range and receiver performance metrics, such as code detection efficiency, rejection coefficient, and noise quotient, were examined and tested among habitats. The results highlighted that the signal from transmitters was successfully detected inside mangrove habitats as well as on the adjacent reef flat. The range to detect at least 50% of transmissions was up to 20 m inside mangroves and up to 120 m outside mangroves. The performance metrics of acoustic receivers inside the mangrove habitat were characterized by low background noise, low rejection rates, and reasonably high code detection efficiency. Furthermore, this study tested the application of this method on juvenile blacktip reef shark Carcharhinus melanopterus and mangrove whipray Urogymnus granulatus, and demonstrated that it can be used to successfully track animals inside mangrove habitat. This novel method could reveal further information on how sharks and rays use mangrove habitats.
RESUMEN
BACKGROUND: Acoustic telemetry has become a fundamental tool to monitor the movement of aquatic species. Advances in technology, in particular the development of batteries with lives of > 10 years, have increased our ability to track the long-term movement patterns of many species. However, logistics and financial constraints often dictate the locations and deployment duration of acoustic receivers. Consequently, there is often a compromise between optimal array design and affordability. Such constraints can hinder the ability to track marine animals over large spatial and temporal scales. Continental-scale receiver networks have increased the ability to study large-scale movements, but significant gaps in coverage often remain. METHODS: Since 2007, the Integrated Marine Observing System's Animal Tracking Facility (IMOS ATF) has maintained permanent receiver installations on the eastern Australian seaboard. In this study, we present the recent enhancement of the IMOS ATF acoustic tracking infrastructure in Queensland to collect data on large-scale movements of marine species in the northeast extent of the national array. Securing a relatively small initial investment for expanding receiver deployment and tagging activities in Queensland served as a catalyst, bringing together a diverse group of stakeholders (research institutes, universities, government departments, port corporations, industries, Indigenous ranger groups and tourism operators) to create an extensive collaborative network that could sustain the extended receiver coverage into the future. To fill gaps between existing installations and maximise the monitoring footprint, the new initiative has an atypical design, deploying many single receivers spread across 2,100 km of Queensland waters. RESULTS: The approach revealed previously unknown broad-scale movements for some species and highlights that clusters of receivers are not always required to enhance data collection. However, array designs using predominantly single receiver deployments are more vulnerable to data gaps when receivers are lost or fail, and therefore "redundancy" is a critical consideration when designing this type of array. CONCLUSION: Initial results suggest that our array enhancement, if sustained over many years, will uncover a range of previously unknown movements that will assist in addressing ecological, fisheries, and conservation questions for multiple species.
