Introduced trout are a leading driver of decline in Australia's native galaxiids, and natural in-stream barriers such as waterfalls play a critical role in excluding trout and sustaining predator-free refugia. Locating these barriers across large, rugged and often inaccessible catchments is a persistent obstacle to conservation planning. Here we demonstrate that high-resolution digital elevation models (DEMs) derived from airborne LiDAR, combined with spatial and hydrological analysis, offer an efficient means of identifying waterfalls and steep gradient breaks likely to act as trout barriers.
A pilot study in the Australian Capital Territory confirmed the value of the approach, directing survey effort toward trout-free headwaters and revealing new populations of galaxiids as well as naturally fishless streams. Building on this, recent surveys in New South Wales have refined the technique — improving how candidate barriers are identified and prioritised — and located further trout-free reaches. These included previously undocumented galaxiid populations alongside both trout-free and fish-free streams.
Together, these results establish LiDAR-based barrier mapping as a repeatable and scalable method for locating refugia and candidate translocation sites. The trout-free reaches identified offer immediate value for the recovery of the critically endangered stocky galaxias (Galaxias tantangara) and other threatened galaxiids, and the workflow is readily transferable to conservation programs across south-eastern Australia.