Assessing abundance when animals are hard to find

Posted on October 1, 2014

Aquatic animals are typically sampled by nets, by electrofishing or by snorkeling. Monitoring the status of rare, secretive and threatened species can be problematic because of the relatively high costs of intensive field surveys, and because there may be prohibitions on trapping or handling. A new and promising alternative approach relies on the fact that it’s possible to detect the presence of DNA released from target species in environmental water samples. The method has been successfully tested with crustaceans, insect larvae, fish, amphibians and mammals. To investigate the precision of the new technique, populations of tailed frogs (Ascaphus montanus) and giant salamanders (Dicamptodon aterrimus) in Idaho streams were sampled using kick-nets and electrofishing. At sites immediately downstream, samples for DNA extraction were collected by pumping one litre of surface water through filters with a 0.45 µm pore size. For both species, the rate of detection was higher for in-stream filtering than for kick-netting or for electrofishing, and DNA concentration increased linearly with animal density and biomass. The precision of the DNA estimates depended on the amount of DNA present in the stream. DNA concentrations didn’t vary significantly with the time of day or a sample’s location in the stream. While research is needed on the effects of different stream conditions on the production, degradation and detection of environmental DNA, these findings open up opportunities for more convenient and cost-effective species monitoring.

Reference: Pilliod, D.S. et al. 2013. Estimating occupancy and abundance of stream amphibians using environmental DNA from filtered water samples. Canadian Journal of Fisheries and Aquatic Sciences 70, 1123–1130.