Using individual‐based movement information to identify spatial conservation priorities for mobile species

Abstract

The optimal design of reserve networks and fisheries closures depends on species occurrence information and knowledge of how anthropogenic impacts interact with the species concerned. However, challenges in surveying mobile and cryptic species over adequate spatial and temporal scales can mask the importance of particular habitats, leading to uncertainty about which areas to protect to optimize conservation efforts. We investigated how telemetry‐derived locations can help guide the scale and timing of fisheries closures with the aim of reducing threatened species bycatch. Forty juvenile speartooth sharks (Glyphis glyphis) were monitored over 22 months with implanted acoustic transmitters and an array of hydrophone receivers. Using the decision‐support tool Marxan, we formulated a permanent fisheries closure that prioritized areas used more frequently by tagged sharks and considered areas perceived as having high value to fisheries. To explore how the size of the permanent closure compared with an alternative set of time‐area closures (i.e., where different areas were closed to fishing at different times of year), we used a cluster analysis to group months that had similar arrangements of selected planning units (informed by shark movements during that month) into 2 time‐area closures. Sharks were consistent in their timing and direction of migratory movements, but the number of tagged sharks made a big difference in the placement of the permanent closure; 30 individuals were needed to capture behavioral heterogeneity. The dry‐season (May–January) and wet‐season (February–April) time‐area closures opened 20% and 25% more planning units to fishing, respectively, compared with the permanent closure with boundaries fixed in space and time. Our results show that telemetry has the potential to inform and improve spatial management of mobile species and that the temporal component of tracking data can be incorporated into prioritizations to reduce possible impacts of spatial closures on established fisheries.

Niche partitioning between river shark species is driven by seasonal fluctuations in environmental salinity

“…Large‐scale seasonal migrations are common among euryhaline elasmobranchs, where these highly mobile predators provide broad and important cross‐biome trophic linkages between tropical freshwater and coastal ecosystems (Every et al., 2017; Matich & Heithaus, 2014). However, moving downstream can also bring potential costs for immature sharks, such as an elevated predation risk (Heupel & Simpfendorfer, 2011), increased resource competition from other marine species (Kinney et al., 2011; Yick et al., 2011) and potential interactions with commercial fisheries (Dwyer et al., 2019; Field et al., 2013). We demonstrated that individuals of both species limited their time in downstream estuarine habitats to only those months when salinities in upstream regions were substantially reduced as a consequence of seasonal increases in freshwater inflow.…”

“…By linking physiological approaches with observations of how animal movements and local environmental parameters change in space and time, it may be possible to reveal mechanistic insights into how environmental variation drives patterns of habitat use, river connectivity and community structure in elasmobranch nursery habitats. Furthermore, having a species‐specific understanding of habitat preferences, ecosystem drivers of animal movements and physiological tolerances can help resource managers identify critical habitat, develop effective by‐catch reduction schemes and forecast population effects caused by natural and anthropogenic changes to the local environment (Dwyer et al., 2019; Horodysky et al., 2015; Whitlock et al, 2015).…”

“…This understanding is important given that tropical rivers and estuaries are increasingly under threat from land clearing, pollution and flow modification (Grant et al., 2019; Lear et al., 2019; Vörösmarty et al., 2010) and by occupying nearshore and inshore habitats, euryhaline elasmobranchs are confined by physical boundaries that limit their ability to evade human‐induced threats (Compagno & Cook, 1995). Given the high susceptibility of euryhaline elasmobranchs and their nursery areas to habitat degradation and modification (Dwyer et al., 2019; Lear et al., 2019), combined with low fecundity, late sexual maturation, naturally low population densities and highly threatened status of all sharks of the genus Glyphis (Ballantyne & Robinson, 2010; Grant et al., 2019; Martin, 2005), there is an urgent need to understand the environmental and physiological factors influencing the occurrence of C. leucas and G. glyphis to predict how these species will respond to environmental change.…”

Sequence analysis and acoustic tracking of individual lake sturgeon identify multiple patterns of river–lake habitat use

“…, Dwyer et al. ). For wide‐ranging and long‐lived species, the need to observe movements of individuals at biologically relevant spatial and temporal scales increases this difficulty even further (Nelson et al.…”

“…Restoration and conservation program guidelines that incorporate behavioral diversity of habitat use can increase resiliency of populations to stochastic environmental events and increase long-term persistence of at-risk species (Alagona et al 2012, Waldman et al 2016. However, developing guidelines to conserve behavioral diversity is difficult because variation at the individual level is infrequently studied despite recognition that habitat use of mobile species is unlikely to fit a generalist pattern (Fodrie et al 2015, Dwyer et al 2019. For wide-ranging and long-lived species, the need to observe movements of individuals at biologically relevant spatial and temporal scales increases this difficulty even further (Nelson et al 2013).…”