Background/Aims
The sawfishes (family Pristidae) are one of the most imperilled groups of elasmobranchs (sharks and rays) globally. Extensive inundation of northern Australian floodplains during the tropical wet season allows Largetooth Sawfish (Pristis pristis) pups to access vast areas of aquatic habitat. As the flooding recedes, sawfish retreat to isolated waterholes where they remain throughout the dry season; if the next wet season rains do not arrive in time, these waterholes dry out and the sawfish perish. A unique long-term collaboration between Indigenous rangers and researchers was launched to search for and rescue trapped sawfish. This study presents ecological findings from these ‘sawfish rescues’, focusing on (a) the history of the rescues, (b) the occurrence of sawfish on the floodplain, and (c) the relatedness of stranded sawfish.
Methods
Stranded sawfish were relocated from near-dry waterholes to the perennial waters of a nearby river during the Sawfish Rescues. Rescue data were compiled between 2012 and 2024 to investigate environmental drivers in both presence, and abundance of juvenile P. pristis on the floodplain between rescue years. A subset of rescued sawfish (n=28) was analysed for genetic relatedness using genome-wide single-nucleotide polymorphism (SNP) data.
Results
A total of 115 juvenile sawfish were successfully rescued over the 12-year period. All rescued individuals were young-of-the-year utilizing shallow water habitat in isolated, disconnected waterholes. Standardised Australian Monsoon Index (AMI) showed a significant positive association with sawfish presence and abundance on the Daly River floodplain. Preliminary kinship analyses of 351 independent pairwise comparisons revealed that 3.7% represented first- or second-order relationships, comprising six full-sibling pairs, three half-sibling pairs, and one putative half-first cousin pair.
Conclusions
This study highlights how cross-cultural science partnerships can deliver effective conservation outcomes. The strong positive association between standardised AMI and sawfish presence, and abundance suggests that young of year sawfish require large wet seasons to access floodplain resources. This emphasizes the ecological importance of lateral connectivity between river channels and floodplain habitats for the survival of juvenile Largetooth Sawfish in the Daly River catchment. Preliminary insights into relatedness analysis suggest that overall relatedness between individuals is low, despite the presence of female philopatry.