GREAT CRESTED NEWTS
Surveys for Great Crested newts Triturus cristatus can be done at different times of year for different purposes. The main aim or requests to do surveys is to potentially collect information to enable a mitigation licence application to be developed and submitted to Natural England. This requires a set of surveys that comply with the recommendations in the Great Crested Newt Mitgation Guidelines (GCNMG) (English Nature 2001). Failure to do this would require an explanation that the surveys done are scientifically sound. This can be done in extreme cases, but the recommendation is to attempt to comply with the GCNMG. The guideline themselves emphasise that they are only guidelines but many regard them as hard and fast rules. They are not. To comply with the 'guidelines' a number of surveys are needed in a guideline defined time window in spring. If the aim of the survey is to determine presence/ absence only then four sessions should be done. If the aim is to potentially submit a mitigation licence application then six sessions will normally be required for a population estimate.
The overall window is Mid-March to Mid-June. However, there is a core window of Mid-April to Mid-May. A number of surveys - either two (for presence/ absence) or three (for a population estimate) - should be within this window. The remainig two or three can be either side of the core window. These dates are sometimes not easy to achieve if there is a cold spring and surveys are not accepted by Natural England if they are done when the overnight air temperature is 5º or lower. This can occur during the early overall window Mid-March to Mid-April. This often means that the non-core surveys are done after Mid-May and all fall in the late overall window of Mid-May to Mid-June.
Presence/ absence survey vs Population estimate
An alternative to presence/absence surveys using standard bottle traps and other methods of survey, there is now an eDNA test that can be done using water samples. This method cannot be used to judge population size and can act as a on-off determination as to whether further standard surveys are necessary. A conclusive negative eDNA taken at an appropriate time and processed in accordance with Natural England guidelines would negate the need to do any further surveys on that pond.
A positive result would trigger the need for further surveys. This may pose a timetabling issue as the earliest a sample can be taken for eDNA is 15 April. The processing time may make it difficult to complete 3 surveys in the core window. Especially as Natural England like to see all surveys well spaced out in the overall survey window, e.g., for a six session survey three should be spaced out in the core window and the remaining 3 should have either two before the start of the core window and one after, or vice versa.
Standard survey should use three methods for presence/ absence - Torch search, bottle trapping and egg searching. For a population estimate only two methods should be used - Torch searching and bottle trapping (eggs searching should not be done).
The GCNMG recommends using a torch with a minimum brightness equivalent to 500,000 candlepower (cp). This is an obsolete brightness unit or brightness measurement and has no recognised conversion to a current standard measure - Lumens (lm). Experimentation by Dryad Ecology proved that a torch that delivered 1,000,000 candlepower penetrated murky water less effectively than an LED torch rated at 200 lumens. Dryad Ecology now use a torch with variable power from 5 - 210 - 500 - 1500 - 3600 lumens. This exceeds the requirements of Natural England and allows the user to avoid potentially causing distress to newts by using the lowest power necessary to be able to see into water of differing clarity, and even the lower setting of 210 lumens exceeds the NE requirement of brightness. Torch searching can be affected by the activity of bottle trapping as discussed below.
Other consultancies normally optimise their time on site by doing their bottle trap installation just before dusk and waiting until dark before doing their torch search. Using standard bottle traps mounted on canes pushed into the bottom of the pond near to the margin normally requires entering the pond to install the traps. This can disturb sediment and make the subsequent torch survey difficult to the point that it may be invalid as Natural England ask for an assessment of turbidity on their licence application form. If the turbidity created by the surveyors is too great then Natural England will raise the issue as a reason why the data may not be secure enough to determine an acceptable survey has been done.
Dryad Ecology always used floating bottle traps launched from the bank without entering the pond and causing turbidity (see innovations). This also has the added advantage that ponds in gardens with butyl liners can be trapped without puncturing the liner with the cane and other difficult ponds like concrete lines ones an also be sampled.
Experience over a number of years by Barry Wright of Dryad Ecology has found that the numbers caught in bottle traps varied greatly from session to session. A recent paper by John Baker (Baker 2013) has shown that using baited traps increases the likelihood of drawing newts in and ensuring that ponds with low number of newts do not rely on their chance encountering of a trap and will be drawn to them by the smell of the bait. he recorded twice the number of GCNs caught compared with un-baited traps (See Innovations).
Floating Bottle Traps
Bottle trapping may be difficult in situations where a cane cannot be pushed into the bottom of the pond either because to pond is butyl-lined and cannot risk being punctured, or because it is concrete-lined and canes cannot penetrate. Ponds with a fringe of vegetation may also pose a problem as it may be difficult to get to free water and even so, the water may be too deep to safely set a trap. Dryad Ecology use floating bottle traps to avoid such problems (See Innovations).
Baker, J. (2013). Effect of bait in funnel-trapping for great crested newts Triturus cristatus and Lissotriton vulgaris. Herpetological Bulletin. 124, 17-20.
English Nature (2001). Great Crested Newt Mitigation Guidelines. English Nature, Peterborough.