Environmental DNA (eDNA) is DNA which is collected from water bodies such as ponds and lakes in which plants and animal live, rather than from the organisms directly. A relatively new technique has been developed in UK where eDNA is used to determine the presence or absence of Great Crested Newts (GCN). DNA from cellular material such as skin, saliva, urine and faeces is deposited in aquatic environments and will then persist for several weeks and can be collected in a water sample.
Currently Natural England guidance on pond survey methods to determine GCN presence or absence requires 4 surveys or 8 visits to a pond during the newt breeding season. At least half of these surveys must be taken within the core period of mid-April to mid-May and make use of three different detection methods (preferably torch survey, bottle trapping and egg searching). The process of eDNA sampling requires a one off collection of water samples to be taken from water bodies with no restriction on time of day as with other methods. The test must be taken during the GCN breeding season, however eDNA persists in the environment for up to 21 days so a test can be undertaken during a longer period between mid-April and mid-June. Samples are then sent off for laboratory analysis.
There are several potential benefits of this technique over conventional survey methods. Natural England has said the research into this technique presented a step forward in making it easier to detect GCN populations. Also as only a single site visit is required it has the potential to make it less costly for developers requiring a GCN survey. Great crested newts are notoriously difficult to detect as they are a fairly cryptic species, therefore the higher accuracy of this method is beneficial. Results from Biggs et. al(2014) found that detection rates using eDNA (99%) were higher than traditional survey methods (95%) therefore even in conditions not conducive to traditional sampling (e.g. murky waters) eDNA sampling may lead to higher likelihood of GCN being detected.
However the eDNA technique does not provide any estimate of GCN population size class, which would be required if a European Protected Species (EPS) licence is needed. If an EPS licence is required a conventional survey would still need to be undertaken to obtain a population size estimate. A population size estimate may also be required for planning authorities to inform mitigation proposals. Results from laboratory analysis can take several weeks which may mean further surveys could not be undertaken in the same survey season.
Therefore eDNA is most suitable for projects with a large number of ponds and waterbodies with a long lead in time. It may also be useful for early stage assessment to clarify presence or absence before further more detailed population size surveys are undertaken. Sites with access restrictions preventing full surveys from being completed may also benefit from the use of eDNA sampling, but only to analyse presence or absence.