Distribution, relative abundance and risks from fisheries to threatened Glyphis sharks and sawfishes in northern Australia

Abstract

Glyphis sharks and pristid sawfishes are globally threatened. While some populations still exist in northern Australia, their distributions are poorly quantified. We used catch records from commercial fisheries and independent surveys to estimate the broad distribution and relative abundances of 2 Glyphis sharks (G. glyphis and G. garricki) and 4 pristid sawfishes (Pristis pristis, P. zijsron, P. clavata and Anoxypristis cuspidata) along the coast, estuaries and river systems of the Northern Territory, Australia. Coarse-scale catch data and records from commercial fishing logbooks that report encounters with Threatened, Endangered and Protected species confirm that small, fragmented populations are distributed across the Northern Territory coastline and suggest limited fishery interactions, although underreporting might occur.KEY WORDS: Sharks · Habitat · Fishing · Conservation · Management · Pristis spp. · Anoxypristis spp. Resale or republication not permitted without written consent of the publisherEndang Species Res 21: [171][172][173][174][175][176][177][178][179][180] 2013 tions, thus hindering conservation planning (IUCN 2010). Two species of Glyphis sharks have been described in northern Australia, G. glyphis (the speartooth shark, previously known as Glyphis sp. A) and G. garricki (the northern river shark, previously known as Glyphis sp. C) (Larson 2002, Martin 2005, Peverell et al. 2006, Compagno et al. 2008, Wynen et al. 2009). Both species have restricted distributions; G. glyphis has only been recorded in the Northern Territory (Adelaide River, East, South and West Alligator Rivers, Murganella Creek and Marrakai Creek) and in Queensland (Wenlock and Ducie Rivers, Port Musgrave and the Bizant River) (Peverell et al. 2006, Compagno et al. 2008. The only other record of this species globally is from Papua New Guinea (Compagno et al. 2008). G. garricki is also found in Australia in the Northern Territory (Adelaide, East and South Alligator and Mary Rivers) but unlike G. glyphis, it has also been recorded in Western Australia (King Sound in the Kimberley region) (Taniuchi et al. 1991, Thorburn & Morgan 2004. Similar to G. glyphis, the only other place where this species has been recorded is Papua New Guinea (Taniuchi et al. 1991, Compagno et al. 2008. Both Glyphis spp. are considered extremely rare, although no population estimates are available for either species. G. glyphis and G. garricki are currently listed as Critically Endangered in the IUCN Red List (www. iucn redlist .org), and critically endangered and endangered under the Australian Commonwealth Environment Protection and Biodiversity Conservation (EPBC) Act 1999, respectively. Due to these classifications, both species are identified as 'key' species for conservation planning (National Oceans Office 2004).There are 4 sawfishes in Australia: the freshwater sawfish Pristis pristis (previously known as P. microdon), green sawfish P. zijsron, dwarf sawfish P. clavata and narrow sawfish Anoxypristis cuspidata (Thorburn et al. 2003, ...

DNA capture reveals transoceanic gene flow in endangered river sharks

“…Although rarely encountered, the available data indicate a broad salinity tolerance with animals observed in freshwater, estuarine, and marine environments. In fact, mature individuals have only been encountered in marine environments (26,27). Further support for regular marine dispersal of Glyphis sharks is provided by a recent phylogeographic study on the speartooth shark G. glyphis, which recovered identical mitochondrial genome sequences in both the Alligator and Adelaide river systems in Australia, and more impressively in both the Wenlock and Alligator river systems, requiring, in the latter case, more than 1,000-km dispersal across marine habitat.…”

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

“…This absence from commercial logbooks is more likely due to misidentification (due to morphological similarities with other captured Carcharhinidae) rather than an absence of an interaction (Field et al. ); a commonly encountered problem when generating conservation plans for cryptic species (Bickford et al. ).…”

“…Despite these limitations, the species’ threatened status, high susceptibility to fisheries (Field et al. ) and the importance of the Wenlock River as a nursery area (Lyon et al. ) highlight a potential conservation issue in immediate need of appropriate mitigation measures.…”

“…Unfortunately, it was not possible to test explicitly whether commercial bycatch of speartooth sharks varied either spatially or between months because no records of speartooth shark interactions with the fishery were logged by fishers in commercial logbooks as part of the Queensland Government commercial logbooks program (http://qfish.fisheries.qld.gov.au/). This absence from commercial logbooks is more likely due to misidentification (due to morphological similarities with other captured Carcharhinidae) rather than an absence of an interaction (Field et al 2013); a commonly encountered problem when generating conservation plans for cryptic species (Bickford et al 2007). However, this does lead to uncertainty about whether our arrangement of time-area closures (or, indeed, any closures informed using telemetry-derived movement information rather than catch data) would directly reduce mortality in speartooth sharks rather than simply reducing spatial overlap.…”

“…This proxy was chosen over barramundi and mud crab catch or catch per unit effort data sets from commercial logbooks because Fisheries Queensland commercial confidentiality rules limited these data to a grid resolution of 30 nautical miles as there were fewer than 5 commercial licenses issued for the area. Despite these limitations, the species' threatened status, high susceptibility to fisheries (Field et al 2013) and the importance of the Wenlock River as a nursery area (Lyon et al 2017) highlight a potential conservation issue in immediate need of appropriate mitigation measures. Perceived benefits will need to be traded off against the feasibility and costs of implementing and enforcing time-area closures and how spatial closures compare with other complimentary management actions that also reduce encounter rates with protected species (e.g., targeted license buybacks) or improve fishing selectivity (e.g., gear alterations, shorter intervals between gear checks).…”