DOI: 10.5061/dryad.pg4f4qrmb
title: Carcharhinus amblyrhynchos and Carcharhinus albimarginatus underwater acoustic telemetry data - Chagos Archipelago 2014-2018

description: A wide array of technologies are available for gaining insight into the
 movement of wild aquatic animals. Although acoustic telemetry may lack the
 fine-scale resolution of some satellite tracking technologies, the
 substantially longer battery life can yield important long-term data on
 behaviour and movement for low per-unit cost. Typically, however, receiver
 arrays are designed to maximise spatial coverage at the cost of positional
 accuracy leading to potentially longer detection gaps as individuals move
 out of range between monitored locations. This is particularly true when
 these technologies are deployed to monitor species in hard-to-access
 locations. We develop a novel approach to analysing acoustic telemetry
 data, using the timing and duration of gaps between animal detections to
 classify movement behaviours into ‘restricted’ or potential wider ‘out of
 range’ movements synonymous with longer distance dispersal. We apply this
 method to investigate spatial and temporal segregation of inferred
 movement patterns in two sympatric species of reef shark within a large,
 remote Marine Protected Area. Drivers of these movements were identified
 using generalised linear mixed models and multi-model inference. Species,
 diel period and season were significant predictors of ‘out of range’
 movements. Silvertip sharks were overall more likely to undertake ‘out of
 range’ movements, compared to grey reef sharks, indicating spatial
 segregation, and corroborating previous stable isotope work between these
 two species. High individual variability in ‘out of range’ movements in
 both species was also identified. We present a novel gap analysis of
 telemetry data to help infer differential movement and space use patterns
 where acoustic coverage is imperfect and other tracking methods
 impractical. In remote locations, inference may be the best available tool
 and this approach shows that acoustic telemetry gap analysis can be used
 for comparative studies in fish ecology, or combined with other research
 techniques to better understand functional mechanisms driving behaviour.
description: Acoustic telemetry data was collected in the BIOT MPA between
 2014 and 2018. Throughout the archipelago there have been situated up to
 93 permanent and temporary acoustic receivers (VR2W, VR4-UWM, VR4G and
 VR2AR receivers, Vemco Inc, Nova Scotia, Canada), as configured in Figure
 1 from Williamson et al (accepted). The BIOT MPA is characterised by
 numerous small islanded atolls with submerged banks and reefs, with depths
 of 1,000 m or more separating each atoll or reef system (Sheppard<i>
 et al.</i> 2013). Acoustic receivers in the BIOT MPA are mainly
 based on areas accessible to divers, such as coral reef systems, with few
 receivers covering the deep pelagic waters of the region.The BIOT MPA
 receiver array was initially started in 2013, and expanded throughout
 subsequent years [for more information see Carlisle <i>et
 al.</i> (2019) and Jacoby <i>et al.</i> (2020)],
 covering a perimeter of 700 km and an area of 25,500
 km<sup>2</sup> within the MPA, for the detection of
 acoustically tagged marine fauna. Of the 93 receivers, 82 are in depths 45
 m or less. All receivers were situated far enough apart to avoid overlap
 in their detection range, with mean distance to closest receiver being
 2.15 km, with a range of 0.55 – 4.57 km.  The raw data
 has been processed to keep only data from 2014-2018, and then processed
 using network metrics such as time difference and self loops, to be used
 to calucate movement data into two movement behaviour types
 'recursive' and 'transitions'.
description: See read me files