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Each factor is scored, and the ten scores are then converted to SI scores using a scale from 0.01 to 1 from graphs given in Oldham et al. (2000) and a HSI result is calculated using the following formula:
Further research by Brady (unpublished) has developed a system for using HSI scores to define pond suitability for Great Crested Newts according to the following categories: • HSI
<0.5 = poor
• HSI 0.5 – 0.59 = below average • HSI 0.6 – 0.69 = average • HSI 0.7 – 0.79 = good • HSI > 0.8
= excellent
There is a positive correlation between HSI scores and presence and abundance of Great Crested Newts in ponds. Generally, ponds with high HSI scores are likely to support larger populations. However, the relationship is not sufficiently precise to conclude that a pond with a high HSI will definitely have a high newt population, or that a pond with a low HSI score will only have a low newt population or no newts at all.
During the HSI visits subjective assessments were also made based on the experience of the surveyor. This means that if ponds were extremely unlikely to support breeding Great Crested Newts then they were discounted at this stage. The HSI data was used to support these decisions. No HSI threshold was employed under which ponds were not surveyed. This resulted in ponds being surveyed even though they had a “Poor” HSI rating. No ponds were discounted with an HSI rating of “below-average” or above.
2.3.5 Presence/Absence Survey Techniques
All water bodies suitable for Great Crested Newts were surveyed four times (where possible) for presence or absence using the following four survey methods (where appropriate).
Egg Searching
This involves searching marginal and aquatic vegetation for Great Crested Newt eggs, which are laid individually on plant leaves, and the leaf folded characteristically around the egg. The large size and yellowish/white coloration readily distinguishes the eggs of Great Crested Newts from those of smaller species.
East Anglia Offshore Wind Limited
Great Crested Newt Survey Technical Report 854188 (Rev 02)