eDNA to study Critically Endangered Sawfish

A large-tooth Sawfish at the Georgia Aquarium. Photo Credit: David Iliff. License: CC-BY-SA 3.0

A new study out in Endangered Species Research uses cutting edge environmental DNA (eDNA) technology to search for critically endangered large-tooth sawfish in Northern Australia. Before heading out to field sites, researchers collected water samples from aquaria to refine their approach and were able to correctly identify which samples came from an aquarium that contained large-tooth sawfish. Then, in collaboration with indigenous rangers, samples were collected from known sawfish habitat around the Daly River, Northern Territory. Previous observation had only sighted sawfish at about half the sites which eDNA results showed were used by sawfish.

While the approach is not yet reliable with samples taken from flowing water, it is mostly accurate with samples from water-holes, and the sensitivity of this kind of testing is expected to continue to improve. This may represent a big breakthrough in monitoring endangered sawfish species: traditional study methods for sawfish, like fishing, observation, or aerial surveys, are expensive and logistically challenging, especially for species with low population numbers in remote habitats. In many parts of the world, sawfish populations are known to have declined, but little more information is available.

Large-tooth sawfish are critically endangered throughout their global range, and their population is believed to be in continuing decline, and to have been reduced by more than 80% since the 1960s. While they are protected in some countries (Australia, India, Brazil, United States, Mexico) it is uncertain whether large-tooth sawfish are extinct in the United States, where the last reported sighting was almost 60 years ago (and where they may have been seasonal visitors, rather than year-round residents). The development of eDNA techniques will make these sorts of questions easier to answer!

You can read the really cool full paper here, or learn more about large-tooth sawfish from the IUCN here. Also keep an eye out for information about an upcoming Field School trip to study small-tooth sawfish in the Caribbean!