Spatio-Temporal Occurrence Patterns of Young Sharks in Tropical Coastal Waters

Abstract

Understanding spatio-temporal patterns in shark occurrence is critical for assessing the ecological role of a species, its vulnerability to human impacts and environmental change, and the efficacy of conservation and management strategies. Investigating these patterns can also develop an understanding of the functioning of coastal shark nurseries. In this context, we undertook a multi-year fisheries-independent survey of shark occurrence along a 400-km stretch of tropical coastline. Logistic regression was used to identify spatial, seasonal and inter-annual variations in the occurrence of neonate and young-of-the-year (YOY) blacktip Carcharhinus limbatus/Carcharhinus tilstoni, pigeye Carcharhinus amboinensis, scalloped hammerhead Sphyrna lewini and spot-tail Carcharhinus sorrah sharks. Results indicated interspecific variations in occurrence. Seasonal variations characterised the occurrence of YOY pigeye, YOY spot-tail and neonate blacktip sharks, whereas spatial variations were more pronounced for YOY blacktip and scalloped hammerhead sharks. These results suggested that the occurrence of young sharks may be more complex than would be predicted by the timing of parturition alone. In addition, spatial heterogeneity in occurrence suggested that proximate bays are likely to vary in terms of the services they provide to young sharks.

Large‐scale eDNA metabarcoding survey reveals marine biogeographic break and transitions over tropical north‐western Australia

“…Northern Australia has a comparatively high elasmobranch biodiversity that includes many large‐bodied and highly mobile species (Last & Stevens, 2009). Variability in species composition is not only influenced by regional conditions, but also reflects the complex life‐history strategies of many elasmobranchs that includes behaviour such as inshore nursery usage (Simpfendorfer & Milward, 1993; Yates, Heupel, Tobin, Moore, et al., 2015; Yates et al., 2015b), partitioning by size and sex (Knip et al., 2012; Yates, Heupel, Tobin, Moore, et al., 2015), and seasonal migration between tropical and temperate waters (Braccini et al., 2018; Heupel et al., 2015). Disentangling such patterns is beyond the capability of presence–absence data alone; however, these data can nonetheless assist in corroborating existing patterns in composition as well as identify new ones.…”

Life history of the common blacktip shark, Carcharhinus limbatus, from central eastern Australia and comparative demography of a cryptic shark complex

“…Large, adult C. limbatus, which are clearly separable from C. tilstoni have been reported in small numbers throughout northern Australia (Stevens and Wiley 1986;Salini et al 2007;Johnson et al 2017). Neonate C. limbatus, also easily separable (Harry et al 2012), have been reported from communal shark nursery areas on both the east and west coasts of Australia (Simpfendorfer and Milward 1993;White and Potter 2004;Gutteridge 2011;Taylor and Bennett 2013;Yates et al 2015).…”

The movement ecology and habitat preferences of the endangered spear tooth shark Glyphis glyphis in the Wenlock River, Northern Australia

“…This establishes the coastal embayment's role as critical wet season habitat for G. glyphis, while also highlighting the importance of Tentpole and Hudson Creeks as important dry season habitat. Temporal partitioning of habitat has been shown previously in other euryhaline elasmobranches (Heupel and Simpfendorfer 2008, Whitty et al 2009, Yates et al 2015). This ability of biotelemetry to obtain long-term and relatively unbiased location information highlights its capacity to identify threats and inform the spatial and temporal scale of management actions for mobile aquatic species.…”