Making the best use of eDNA survey for great crested newts – opportunities and limitations (January 2016)

Making the best use of eDNA survey for great crested newts – opportunities and limitations (January 2016)

Environmental DNA (eDNA) testing is a relatively new survey technique that can help determine the presence or absence of great crested newts in ponds. Since this is still a relatively new approach its practical application and limitations for field surveys some uncertainty remains in the ecology sector about how it should be best applied and what its practical limitations might be. This article discusses the potential applications of the process, and our perceptions of its limitations, which should be considered when planning survey work for great crested newt.


Great crested newt DNA is released into aquatic environments through shed skin cells, urine, faeces and saliva. It can persist in water for several weeks, can therefore be collected, and a test has been developed for detecting the eDNA of the species. This has been found to be an effective way to determine presence or absence of newts, but there are some limitations that should be borne in mind and which we expand upon below.

A detailed sampling and analysis protocol has been devised and, providing this is followed, both Natural England and Natural Resources Wales will accept eDNA test results as evidence of presence or absence (Scottish Natural Heritage does not yet have a formal position statement on eDNA).

Water samples need to be gathered between 15 April and 30 June. If sampling is scheduled for mid-April, Natural England’s advice is that great crested newts should be demonstrably active at the time of the sampling, or that conditions in the local area should have been suitable (for newt activity) in the two weeks prior to the sampling date. Samples are then sent to a recognised laboratory for analysis. Several laboratories now offer an eDNA service through it is advisable to ensure that the sampling kits and the testing procedure being used comply with the DEFRA guidance. The analysis time required for a sample has reduced significantly since the technique was first trialled; some laboratories offer fast track testing, which can take as few as five working days.

Since only one survey visit is required, in some circumstances eDNA survey has potential to reduce the level of survey effort which until now has been routinely required to determine presence or absence of great crested newt (i.e. four survey visits, each including evening and morning survey, between April and June). The cost saving potential is also obvious.

eDNA testing also provides an opportunity to undertake presence/absence survey from mid-May onwards when it might otherwise be too late to start a full programme of survey using conventional survey techniques.

The technique and the use of its results are not, however, without limitations; and since these are potentially significant it is important they are considered when devising a survey approach for any particular project.

Potential limitations

  • Currently, for presence/absence surveys, eDNA can only be sampled between 15 April and 30 June. Although samples taken outside this period can show presence (say, if larval newts are in a pond) such samples cannot be used to determine absence.
  • The eDNA test result cannot currently provide a population size class assessment (i.e. newt abundance). Where this is required (for licencing) conventional survey techniques are likely to be more appropriate (this is detailed further below).
  • If a positive eDNA result is returned, sufficient time needs to be allowed to carry out any additional survey required (say, for licensing purposes – see below). Since conventional survey involves repeat visits between mid-April and mid-May, unless the eDNA result is obtained early in the season, fitting in additional survey may be a problem.
  • In certain situations eDNA survey results may not always be conclusive. Since eDNA can be patchy depending where animals have been in a pond, sampling in multiple parts of a pond increases the chance of successfully collecting eDNA. There is a risk that poorly accessible ponds with few available sampling points will not allow sufficient samples to be taken to confidently conclude that GCN are not present.
  • The presence of sediment and algae in samples can inhibit the laboratory test for eDNA.
  • Although a licence is not required to take water samples, Natural England has advised that eDNA water samples would need to be collected by a licenced newt surveyor (or accredited agent) if survey results are to be provided in support of an European Protected Species (EPS) licence application (presumably to demonstrate proof of absence, where relevant).

Licensing, population size class assessment and timing constraints

If great crested newts are found to be present and considered likely to be affected by a development proposal, then a European Protected Species (EPS) licence is likely to be required for that development. An EPS licence application requires a population size class assessment, which currently involves six survey visits using conventional survey techniques; this would still be required.

Typically two weeks (or if using a fast tracked service, at least five working days) need to allowed for sample analysis. Given the limited survey window for carrying out conventional survey it is important to consider how to allow sufficient time to undertake both eDNA analysis and, if necessary, any additional population size class assessment survey work in the same survey season.

If there is a chance that a licence is needed, it may be advisable, therefore, to carry out one or two conventional survey visits in the early part of the survey period, concurrently with eDNA sample collection and analysis, to ensure all required data can be obtained within one season.  Conventional survey work can be discontinued if a negative eDNA result is returned.

This  difficulty is likely to be usefully overcome on larger scale projects with a sufficient lead-in time to allow eDNA survey work to be carried out in year one and any additional survey required in year two. This approach is likely to be cost effective as it would potentially allow some ponds, those where great crested newt absence is confirmed by the test, to be scoped out of any further assessment.

Thoughts on potentially useful applications at this time

Although the eDNA test has limitations, meaning that conventional survey techniques will often still be required, it is likely to prove most useful in the following scenarios:

  • As a cost effective way of scoping future survey requirements (i.e. population size class assessment surveys) for projects where there is sufficient time available to carry out the detailed (conventional) survey the following year.
  • For accessible ponds where the required number of suitable sampling points can be achieved and where water samples can be taken with a low sediment and algal loading.
  • To confirm absence in ponds that are considered to have low potential to support great crested newts but where further confirmation is required (say, to provide greater confidence in an assessment of likely absence). This is particularly where the likelihood and significance of possible impacts on great crested newts is considered to be low.
  • For ponds with higher potential to support great crested newts, and where a key part of the conventional survey period (mid-April to mid-May) has been missed, but where there is still time available to collect eDNA samples (before 30 June). In this situation, an eDNA finding of “absence” would avoid the need for further conventional presence/absence survey. Note: if population size-class information is required (say, to support an EPS licence application) this would still need to be collected through the conventional six-visits the following spring.
  • Population size class assessment is not required on every project and, thus, where presence/absence surveys are considered adequate (for instance in support of work with low risk of impact) eDNA survey is more likely to be a useful and conclusive tool.

BSG Ecology has extensive experience in great crested survey and mitigation, including major infrastructure project work involving thousands of newts and complex EPS licensing. We have numerous licenced great newt surveyors throughout our various offices and we have undertaken eDNA survey work since in 2014.

We are always happy to discuss projects or issues – please contact us for further information. For specific enquiries about eDNA please contact Guy Miller (Hathersage – 01433 651869), Steve Betts (Newcastle – 0191 303 8964), Anna Muckle (Oxford 01865 883833) or Jim Gillespie (Newport – 01633 509000).

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