Observations on the distribution, biology, short-term movements and habitat requirements of river sharks Glyphis spp. in northern Australia

The genus Glyphis comprises a group of rare and poorly known species. G. glyphis and G. garricki are found in northern Australia, and both species are listed as Critically Endangered C2a(i) on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. We collated all available records of G. glyphis and G. garricki in Australia to gain an understanding of the species' distribution and biology. All records of G. glyphis (n = 106) were confined to 9 tropical rivers and estuaries north of 15° S. G. garricki (n = 32) were captured in 4 rivers and estuaries as well as in marine environments north of 18° S. Both species can be classified as euryhaline elasmobranchs. Parturition is thought to occur in October to December, and size at birth for both species is around 50 to 65 cm total length (TL). Two male G. garricki were mature at 142 and 144 cm TL, 2 females of 177 and 251 cm TL were mature, with the smaller animal having 9 early-stage embryos in utero. No mature G. glyphis have been recorded to date. Short-term movement patterns of 3 G. glyphis were investigated in the Adelaide River (Northern Territory) using acoustic tags. Animals were tracked for 27.8, 27.0 and 50.2 h respectively and displayed up-and downstream tidally assisted movement, moving on average 10 to 12 km per tide. The limited distribution, specific habitat requirements and repeated use of available habitat make Glyphis species particularly vulnerable to localised overfishing and habitat degradation. These findings highlight the need for additional research and the implementation of national recovery plans for both species. © Inter-Research 2009.