Telemetry reveals spatial separation of co-occurring reef sharks

The ability to understand the functioning of ecosystems requires an understanding of the role individual or groups of species play within that environment. Defining ecological roles is challenging in complex ecosystems such as coral reefs. While it is well known that multiple reef-associated shark species coexist on a single reef, their patterns of space use and interactions have been difficult to define. Here we used acoustic telemetry data to analyse activity space, depth use and spatial networks to examine the interplay of these species relative to their roles in coral reef ecosystems. Integration of multiple analyses revealed that species with similar sizes and similar diets displayed clear spatial segregation, both between habitats and depth. This distribution is likely to reduce competition for prey among these species. In contrast, species that are dietary generalists or that have unique diets moved more broadly and overlapped with all other species. These results suggest competition for prey may be a driving factor in the distribution and space use of reef-associated sharks, revealing complex, interdependent functional roles within these systems. Results of this analysis demonstrate the advanced information that can be obtained through application of multiple methods and directed, simultaneous study of multiple species

A multilayer perspective for inferring spatial and social functioning in animal movement networks

Animal movement patterns are increasingly analysed as spatial networks. Currently, structures of complex movements are typically represented as a single-layer (or monoplex) network. However, aggregating individual movements, to generate population-level inferences, considerably reduces information on how individual or species variability influences spatial connectivity and thus identifying the mechanisms driving network structure remains difficult. Here, we propose incorporating the recent conceptual advances in multilayer network analyses with the existing movement network approach to improve our understanding of the complex interaction between spatial and/or social drivers of animal movement patterns. Specifically, we explore the application and interpretation of this framework using an empirical example of shark movement data gathered using passive remote sensors in a coral reef ecosystem. We first show how aggregating individual movement networks can lead to the loss of information, potentially misleading our interpretation of movement patterns. We then apply multilayer network analyses linking individual movement networks (i.e. layers) to the probabilities of social contact between individuals (i.e. interlayer edges) in order to explore the functional significance of different locations to an animal’s ecology. This approach provides a novel and holistic framework incorporating individual variability in behaviour and inter-individual interactions. We discuss how this approach can be used in applied ecology and conservation to better assess the ecological significance of variable space use by mobile animals within a population. Further, we argue that the uptake of multilayer networks will significantly broaden our understanding of long-term ecological and evolutionary processes, particularly in the context of information or disease transfer between individuals

Network analysis and theory in shark ecology - methods and applications

In recent decades, network analyses have become ubiquitous in ecology, facilitating our understanding of linkages between paired entities, whether it be genes, proteins, individuals, species, or habitats (Blüthgen et al., 2008; Croft et al., 2008; Krause et al., 2007; Proulx et al., 2005; Wey et al., 2008). Network theory (also known as graph theory) originates from the mathematical and social sciences but has developed concurrently across many disciplines, including computational science, physics, management, genetics, and epidemiology (Newman, 2010), to name but a few

Dispersal patterns of largemouth bass and smallmouth bass following early-, mid-, and late-season fishing tournaments in an Eastern Ontario Lake

Black bass fishing tournaments with conventional weigh-ins tend to displace fish from their capture site and often release fish within close proximity to the weigh-in site. Tournaments often include Largemouth Bass Micropterus salmoides and Smallmouth Bass M. dolomieu and occur throughout fishing seasons; however, there have yet to be any systematic congeneric comparisons across different seasons. Objectives of our study were to (1) assess post-tournament dispersal of Largemouth Bass and Smallmouth Bass (i.e., short-term stockpiling-accumulation of fish around weigh-in site <1 month after tournament) across seasons, and (2) determine the success of return to the main basin. Research took place on Big Rideau Lake in eastern Ontario and included a preseason control (N = 30) where fish were captured, acoustically tagged, and released at the site of tournament weigh-in (Rideau Ferry). Tournament-caught bass (N = 88 total) were tagged at three tournaments that spanned June (early season), August (midseason), and October (late season). Our results indicated a brief short-term stockpiling (within 300 m) in all seasons, and all detected fish eventually returned to the main basin. Tournament-caught Largemouth Bass tended to take longer to disperse from the release site following the midseason tournament (4.6 d); Smallmouth Bass tended to disperse from release site <1 d following all treatments. Similarly, tournament-caught Largemouth Bass exposed to the midseason tournament tended to take the longest to redistribute to the main basin (238 d) in comparison to other treatments. Although Smallmouth Bass tended to redistribute to the main basin faster than Largemouth Bass, late-season Smallmouth Bass tended to redistribute the slowest (101 d) following tournament release. Although fish do survive and eventually return to the main basin, displacement may have broader ecological consequences (i.e., large-scale displacement of top predators, adverse effects on recruitment) such that there would be merit in more catch-weigh-release formatted events

Appendix E. Summary plots of general linear models showing factors that influenced network metrics of Carcharhinus albimarginatus and C. leucas.

Summary plots of general linear models showing factors that influenced network metrics of Carcharhinus albimarginatus and C. leucas

Appendix G. Summary of link or "corridor" importance to the connectivity of reef-associated sharks in the Great Barrier Reef.

Summary of link or "corridor" importance to the connectivity of reef-associated sharks in the Great Barrier Reef

Appendix B. Location of acoustic telemetry arrays along the Queensland coast of Australia.

Location of acoustic telemetry arrays along the Queensland coast of Australia

Appendix F. Centrality metrics of Carcharhinus amblyrhynchos, C. albimarginatus, and C. leucas monitored in the central Great Barrier Reef.

Centrality metrics of Carcharhinus amblyrhynchos, C. albimarginatus, and C. leucas monitored in the central Great Barrier Reef

Appendix D. Summary plots of general linear models showing significant effects of fork length and sex on network metrics for Carcharhinus amblyrhynchos.

Summary plots of general linear models showing significant effects of fork length and sex on network metrics for Carcharhinus amblyrhynchos

Appendix A. Description of the study reefs and estimated acoustic coverage, central Great Barrier Reef of Australia.

Description of the study reefs and estimated acoustic coverage, central Great Barrier Reef of Australia