25 October 2021
Sawfish are swimming out of time
Published online 22 February 2021
Predictions indicate that sawfish are nearer to extinction than previously thought.
On land, ecologists track extinction based on a decline in sightings of animals over time. But this approach does not work in the vast oceans. An international research collaboration, including a scientist from the United Arab Emirates, has now developed an approach to track the downward trend of sawfish population numbers, and what’s driving their decline. With predictive modelling, the research team expect that the peculiar-looking sawfish is extinct in 55 of the 90 countries whose coastal waters were once their home.
Sawfish are one of the most valuable internationally traded animals. They’re an important source of food, their saw-like rostra are traded as curios and for medicine, and their rostral teeth are harvested for cockfighting spurs. Three of the five sawfish species are Critically Endangered, with the other two listed as Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.
Helen Yan, from Simon Fraser University, Canada, who led the collaboration, says her project followed a huge data gathering mission in 2014, in which the IUCN Species Survival Commission (SSC) Shark Specialist Group worked with local fishermen around the globe who tracked when and where they encountered sawfish. This led to the creation of sawfish distribution and local extinction maps.
Armed with these maps and the knowledge of local conditions, Yan and her team were able to discern variables that most correlated to sawfish decline. They found overfishing and habitat loss are the “two biggest factors” driving sawfish towards extinction, says Yan. This data also allowed the researchers to predict that sawfish are locally extinct in nine more countries than the originally presumed 46.
Using a ‘space-for-time’ approach, the team tracked population decline by tracking the changing spaces that sawfish inhabit. “If you have a species that used to be found in every country across the globe, and now they’re only found in one or two, we can confidently say their population numbers are declining,” Yan explains.
Colin Simpfendorfer, director of the Centre for Sustainable Tropical Fisheries and Aquaculture at James Cook University, Australia, and co-chair of the ICUN SSC Shark Specialist Group says this research identifies nations that could be critical for stopping the global extinction of sawfish and the actions that can be implemented. The paper recommends a list of nations in which sawfish protections could be enforced and would increase to 71.5% the protection of sawfishes’ historical distribution.
One of the most simple and effective methods is for a country to implement a ban on keeping sawfish if they’re caught. “It’s now a case of nations taking responsibility for sawfish conservation,” he says.
Yan, H. F. et al. Overfishing and habitat loss drives range contraction of iconic marine fishes to near extinction. Sci Adv 7, eabb6026 (2021).