Abstract
A wide array of technologies are available for gaining insight into the movement of wild aquatic animals. Although acoustic telemetry can lack the fine‐scale spatial resolution of some satellite tracking technologies, the substantially longer battery life can yield important long‐term data on individual behavior and movement for low per‐unit cost. Typically, however, receiver arrays are designed to maximize 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.Here, we develop a novel approach to analyzing acoustic telemetry data, using the timing and duration of gaps between animal detections to infer different behaviors. Using the durations between detections at the same and different receiver locations (i.e., detection gaps), we classify behaviors 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 (MPA). Response variables were generated using network analysis, and drivers of these movements were identified using generalized linear mixed models and multimodel 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 with gray 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 are impractical at scale. 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 behavior.
Highlights
Biologging and biotelemetry are ubiquitous in aquatic ecology, revealing important insight into the movement patterns of a broad spectrum of species (Block et al, 2011; Carrier et al, 2018; Hussey et al, 2015)
Gaps might be used to inform the likelihood of fish moving out of marine protected areas (MPAs) into unprotected waters, where they may be vulnerable to exploitation from commercial fisheries (Carlisle et al, 2019)
To explore putative spatial and temporal segregation between gray reef and silvertip sharks, “restricted” versus “out-of-range” movements were included as a binary response variable and “species” was included as interaction term with all explanatory variables and individual ID as a random factor
Summary
Biologging and biotelemetry are ubiquitous in aquatic ecology, revealing important insight into the movement patterns of a broad spectrum of species (Block et al, 2011; Carrier et al, 2018; Hussey et al, 2015). Gaps might be used to inform the likelihood of fish moving out of marine protected areas (MPAs) into unprotected waters, where they may be vulnerable to exploitation from commercial fisheries (Carlisle et al, 2019) These gaps can be used to estimate the timings of ontogenetic habitat shifts, when individuals begin leaving nursery areas for longer periods (Poulakis et al, 2013), as well as for more accurately determining the timings and thresholds to define residency events for spatial distribution and movement analyses (Chapman et al, 2019). Our aim was to (1) develop and test an approach for identifying informative detection gaps between movements from acoustic telemetry data; and (2) combine this approach with information-theoretic modeling to analyze and assess the potential of detection gaps to investigate differential movement patterns and segregation in sympatric species
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