Threatened fishes have suffered significant range reductions due to alien fishes, remaining only in isolated headwater refugia. Barriers like waterfalls prevent invasion by alien fish, however suitable waterfalls are scarce and often in remote locations. Their remoteness means current methods for finding them are inefficient, and surveys are expensive. As such, locating remnant populations of many threatened species is hard to prioritise and requires knowledge of potential to improve distributional knowledge and find suitable translocation sites for conservation.
Lidar-derived elevation models were used to find waterfall barriers in headwater streams, and fish community was determined using backpack electrofishing. Waterfall height and gradient was examined to investigate patterns in streams where invasion by alien species has occurred. These characteristics partitioned barrier and non-barrier sites, with aliens rarely found upstream of waterfalls greater than ~1 m high. Several previously unknown barriers and populations of native fish were discovered using this new method.
Lidar-derived elevation modelling provides am effective approach to locate and prioritise barriers in remote locations, and provide insight into distribution of native and alien fishes. This approach means funding may be spent more efficiently on targeted surveys.