Evaluation of visual encounter surveys as a method for the rapid assessment of fish presence and relative density in high mountain lakes

Introduced fish are a widespread ecological threat in originally fishless high mountain lakes. However, basic distribution data largely missing for most regions. Using time-consuming standard methods (e.g. Nordic fishing nets) to assess and relative densities at relevant spatial scale can be impracticable, because of the large number To overcome this problem, alternative rapid monitoring would helpful. Visual encounter survey (VES) is candidate method that enables observing from shoreline. It takes only minutes implement already widely used amphibian lakes ponds. VES was evaluated as introduced salmonids cyprinids (the families) 52 The probability detecting both families by rapidly approaches 100% increase, false absences restricted populations living low densities. also provides simple indications about densities, distinguishing between high-density low-density populations. As usually does not enable species identifications, we propose useful describe inventories, needing taxonomic detail, but necessary planning large-scale conservation measures.