Use of eDNA for detecting great crested newts – how effective is it?

Use of eDNA for detecting great crested newts – how effective is it?

In this article we consider the use of eDNA analysis of water samples to detect great crested newts, and discuss the results of some recent survey work.  Whilst we identify limitations that need to be considered, it is also recognised that the technique provides a useful additional method for detecting great crested newts, and we use it in appropriate circumstances at sites throughout the UK.  The method has been endorsed by Natural England and Natural Resources Wales.

The use of environmental DNA  – Natural Resource Wales

In 2014 BSG Ecology was faced with an interesting dilemma for a proposed development in North Tyneside, when the client decided to submit a revised planning application for a site in June.  The development site included a number of ponds, some of which had previously been found to support small populations of great crested newts.  Unfortunately the existing survey data were not up-to-date and the late commissioning of the work meant that the survey window in 2014 had been missed for this species.

It was decided to use the eDNA analysis technique to complement the previous survey results and to confirm the presence or likely absence of great crested newts in all ponds.  In addition, two ponds outside the site, both of which are known to support small populations of great crested newts, were sampled to provide positive controls (one of the ponds had been surveyed earlier in 2014 and so recent data were available).  Water samples were collected within the specified survey window for eDNA analysis, and in accordance with the published methodology[1].

Surprisingly the results of the eDNA analysis were negative for all ponds, including the two positive control ponds outside the site boundary.  The negative results for ponds located within the site were not unexpected as these had low Habitat Suitability Index[2] scores and previous survey work had only detected very low numbers of newts in two of the ponds (and the remaining two ponds were ephemeral).  However, the negative results for the two control ponds were a surprise and highlighted a potential issue with the eDNA method, namely false negative results.

The eDNA method has been identified by Natural England[3] and others as potentially providing a useful alternative method for confirming the presence or likely absence of great crested newts. However, the occurrence of false negative (and false positive) results potentially represent a significant limitation for the technique.  A recent study undertaken by Defra in 2014[4] has evaluated the robustness of the methodology using mathematical modelling as well as tests in the laboratory and in the field.

Five different situations were tested for, and the results obtained are summarised as follows:

  • Out of range false positives (samples were taken from ponds in Cornwall out of great crested newt range) – no false positives were recorded .
  • Comparison with ‘traditional’ survey techniques – evidence of great crested newt was detected at 99.3% of sites by the eDNA method compared with 95% detection for combined traditional methods.
  • Occurrence of false negatives – 8.8% of the samples gave a false negative result.
  • Within range false positives (sites were selected that were very unlikely to support great crested newt) – no false positives were recorded.
  • Sampler variability – sampler variability was low with any variation being attributed to very low DNA occurrence.

The Defra study has suggested that the occurrence of false negative results is mostly attributable to three key factors:

  • Low numbers of newts.
  • Large shallow pond margins (which may be unattractive to newts).
  • Restricted access for sampling.

The Defra study is small-scale and consequently provides a relatively simplistic analysis of the eDNA method.  One notable gap in the results is whether or not the reliability of the method varies throughout the year as the number of newts in a pond would be expected to increase or decrease.  It is also unclear how efficient the method is at detecting transient animals that visit a site only briefly.  Defra conceded that “this could have a substantial impact on the practical use of the method”.

Based on our own experiences and having reviewed the Defra study, we have concluded that the eDNA method is capable of detecting very small populations of great crested newts where there is continuous pond occupancy and/or breeding.  However, significant limitations remain which can be summarised as follows:

  • eDNA cannot currently be used to estimate population size and so traditional methods will still need to be employed where the presence of great crested newts is confirmed and work is planned that requires a European protected species licence.
  • Where only very small populations are present (and/or where occupancy may not be continuous) eDNA survey may not be able to confidently conclude that newts are absent from a pond.

It seems therefore that although the eDNA technique provides a useful additional method for detecting great crested newts, the limitations of the technique need to be fully considered when deciding where, when and how to use it.  The potential for the occurrence of a false negative result needs to be understood and negative results should be treated with some caution as  the presence of a small, undetected population of great crested newts cannot necessarily be ruled out. Finally, it should be borne in mind that the issue of false negative results can, of course, be a problem with the more conventional survey methods and the benefits and limitations of all survey techniques need  to be taken into account when designing a survey programme.

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 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)

Jim Gillespie (Newport – 01633 509000).

[1] Williams, P. (2013). How to collect a water sample to detect Great Crested Newt eDNA. GCN eDNA protocol, Freshwater Habitats Trust. August 2013.

[2] Oldham, R.S., Keeble, J., Swan, M.J.S. and Jeffcote, M. (2000) Evaluating the suitability of habitat for the great crested newt (Triturus cristatus), Herpetological Journal, Vol.10, pp.143-155.

[3] https://www.gov.uk/great-crested-newts-protection-surveys-and-licences (accessed 23 January 2015).

[4] Biggs J, Ewald N, Valentini A, Gaboriaud C, Griffiths RA, Foster J, Wilkinson J, Arnett A, Williams P and Dunn F 2014. Analytical and methodological development for improved surveillance of the Great Crested Newt. Appendix 5. Technical advice note for field and laboratory sampling of great crested newt (Triturus cristatus) environmental DNA. Freshwater Habitats Trust, Oxford.

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Top Photograph: Natalie White, BSG Oxford

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