Field assessment of great crested newt Triturus cristatus mitigation projects in England.

The status of great crested newts at 13 sites that have been subjected to mitigation before 2002 was assessed by standardized surveys carried out during March-May 2005. Ponds on the mitigation sites (n=31 in total) were each surveyed four times over this period by a combination of torch counts, bottle trapping and mark-recapture population estimates.

The quality of pre-development information on the sites was extremely variable. Moreover, because of (1) the paucity of standardized pre-development population assessment data; and (2) changes in the aquatic and terrestrial habitats at the sites, comparisons of the current population assessments with historical data were difficult.

A combination of the English Nature (2001) and Griffiths and others. (1996) scoring systems suggested that four of the sites contained ‘small’ populations; four sites contained ‘small-medium’ populations; four sites contained ‘medium’ populations; and one site contained a ‘medium-large’ population. In terms of presence or absence of newts, those ponds and associated terrestrial habitats that had relatively high Habitat Suitability Indices (HSIs) generally contained great crested newts. However, as some sites with high HSIs had low counts of newts by torching or trapping, the relationship between HSIs and newt counts was weak. Although many of the sites contained appropriate aquatic and terrestrial habitats for newts, the majority were very isolated by development and had poor connectivity to other suitable habitats. Nevertheless, two ponds at different sites supported ‘medium to large’ numbers of newts despite high levels of fragmentation, development and connectivity to just one and two other ponds respectively. The level of ongoing survey and management at the sites varied, with some sites suffering from a lack of both activities.

The data show that great crested newt populations can be maintained at sites subject to development mitigation. However, further surveys are needed to assess the long-term viability of these populations. Equally, more attention needs to be placed on ensuring habitat connectivity and long-term management plans for such sites.