Seasonal use of a macrotidal estuary by the endangered dwarf sawfish, Pristis clavata

Abstract

1. Sawfishes (Family: Pristidae) are one of the most imperilled fish families worldwide. There is an increasingly urgent need to better understand the biology, ecology, and population status of the five sawfish species to develop more effective conservation measures. The dwarf sawfish, Pristis clavata, is one of the least researched members of the pristids, with literature limited to analysing disparate datasets or collations of rare encounters in northern Australia.2. This study examined the spatial ecology of dwarf sawfish using targeted surveys and acoustic telemetry to determine its habitat use in a macrotidal estuary in northern Australia. Seventeen dwarf sawfish were tagged with acoustic transmitters and monitored in the Fitzroy River estuary and adjacent King Sound (Kimberley, Western Australia) between August 2015 and November 2017.3. Dwarf sawfish observed within the Fitzroy River estuary and King Sound were juveniles, ranging between 740 and 2,540 mm in total length. Catch per unit effort of dwarf sawfish in the late dry season was relatively high in the estuary, with the catch rate in 2015 being one of the highest reported for any sawfish species.4. Acoustic detections revealed a distinct seasonal pattern in the use of different parts of the estuary and King Sound, which was found to be driven by salinity.Dwarf sawfish predominately occupied a single large pool near the terminus of the tidal limit in the late dry season (August-November), before transitioning to regions in closer proximity to the river mouth or in King Sound in the wet and early dry seasons (December-July).5. Given the high abundance and residency of dwarf sawfish in the Fitzroy River estuary, this area is an important nursery for the species during the late dry season and should be formally recognized as a habitat protection area for the species.

Monsoonal wet season influences the migration tendency of a catadromous fish (barramundi Lates calcarifer)

“…During large flooding events, the estuarine reaches of floodplain rivers in northern Australia often become almost entirely fresh (Morgan et al., 2021), and coastal floodplains adjacent to estuaries may be continuously inundated with fresh water for several months (Pettit et al., 2011). As such, some estuarine habitats are fresh in wet, strong monsoonal, years, but saline in dry, weak monsoonal, years.…”

A review of the life history and ecology of euryhaline and estuarine sharks and rays

“…Short-term movement ecology is thought to follow tidal cycle and direction for eight species (27.6%; five euryhaline [50.0%], three estuarine [15.8%]: C. leucas [Pillans 2006;Ortega et al 2009;Pillans et al 2020], G. glyphis [Pillans et al 2008;Pillans et al 2009], P. pristis [Whitty et al 2009;Buckley et al 2020], U. dalyensis [Campbell et al 2012], H. sabinus [Brinton and Curran 2017], P. ater [Martins et al 2020], P. clavata [Stevens et al 2008], P. zijsron [Morgan et al 2017]). Ten species undergo seasonal migrations in response to environmental factors such as salinity and temperature (34.4%; five euryhaline [50.0%], five estuarine [17.2%]: C. leucas Espinoza et al 2021], G. glyphis [Lyon et al 2017;Dwyer et al 2019;Pillans et al 2022], P. pristis [Peverell 2009], H sabinus [Ramsden et al 2017;Brinton and Curran 2017], U. dalyensis [Campbell et al 2012], F. colarensis [Last et al 2016a], P. clavata [Morgan et al 2021], P. pectinata [Simpfendorfer et al 2011], P. zijsron [Morgan et al 2017], R. bonasus [Collins et al 2008;Fisher et al 2013]) (Online Resource 3).…”

“…Euryhaline and estuarine species are benthic, demersal, and pelagic in marine waters, estuaries, rivers, floodplains, and lakes (Online Resource 3). Seven species ( 24 , G. glyphis [Feutry et al 2017], P. pristis [Whitty et al 2009], H. guttatus [Yokota and Lessa 2007;Gianeti et al 2019 [Last et al 2016b], A. cuspidata [Peverell 2005], P. clavata [Morgan et al 2021], P. pectinata [Poulakis et al 2011], P. zijsron [Morgan et al 2017]). Depth partitioning where neonates and juveniles usually occur in shallow water and adults move into deeper waters is common in species with high levels of information on habitat use (as above, excluding G. glyphis).…”

“…Euryhaline species tend to follow predictable downstream and upstream movements in response to seasonal flow, salinity, dissolved oxygen, and temperature (e.g., C. leucas, G. glyphis [Dwyer et al 2020;Pillans et al 2020]). There is also evidence of migrations in response to environmental factors in estuarine species (e.g., P. clavata [Morgan et al 2021], P. pectinata [Simpfendorfer et al 2011], P. zijsron [Morgan et al 2017], R. bonasus [Collins et al 2007;), suggesting that euryhaline and estuarine species use behaviour to reduce metabolic demands (e.g., osmoregulation, thermoregulation; Lyon et al 2017). Many euryhaline and estuarine elasmobranchs also use the physical characteristics of their environment, such as the strong tidal flows of tropical river systems to reduce the energy expenditure of movement by moving with tidal cycles (e.g., G. glyphis [Lyon et al 2017], U. dalyensis [Campbell et al 2012]; H. sabinus [Brinton and Curran 2017]).…”

Collaborative methods identify a remote global diversity hotspot of threatened, large‐bodied rhino rays

“…Particular regions within Australia are recognized for their populations of large‐bodied rhino ray species, with most of these occurring in the more remote areas of northern Australia. For example, globally important long‐term nursery habitats for dwarf, green and largetooth sawfish have been identified in the Kimberley and Pilbara regions in Western Australia (WA) (Morgan et al, 2011; Morgan et al, 2015; Lear et al, 2019; Morgan et al, 2021).…”