Typical methods for estimating fish abundance from a lake involve netting a number of fish from different areas and then extrapolating from there. But this method, though used in many different studies over the years, is not the easiest or cheapest way to make such assessments. A better way, find scientists from the Universite Laval and Quebec’s Ministry of Forests, Wildlife and Parks, is to use environmental DNA. That’s the stuff that is left in the water by fish as they swim, forage and mate — as they carry out their lives, in other words. This type of DNA, commonly called “eDNA,” can be found in all waterways. Researchers from the two institutions began their work looking at lake trout populations in 12 lakes throughout the Canadian province of Quebec. They already had access to old lake trout population estimates, obtained through the netting and extrapolating method, with which to compare the results of their new approach. Instead of using nets, the scientists relied on eDNA present in the lakes, the kind of genetic material that can be linked back to cells that have come off fish skin within a period of a few days. To gather the eDNA, researchers took 10 one-liter samples from each lake, with each coming from a different part of each lake. Researchers then filtered the water and subjected the particles to genomic analysis techniques to accurately measure the quantity of lake trout DNA. They found a strong correlation between population estimates obtained using the traditional approach and those based on the new eDNA technique. In addition, the variations in eDNA abundance were found to be similar to those reported for net catches. This means that the new method can provide results just as accurately and reliably as the netting method, but at a potentially much lower cost. The scientists add that applications for eDNA aren’t limited to assessing fish populations in lakes. The approach could also be used successfully for estimating the populations of fish in rivers, covering such important species such as salmon. Up next for the researchers is to produce tools that allow for the genomic targeting of several key fish species. These include the likes of walleye, sauger, brook trout, Arctic char and northern pike. But efforts are also being focused on some rare or threatened fish species out there, as well as invasive fish species that managers want to get rid of. Full results of the work are published in the Journal of Applied Ecology.