The Conservation of the Scarce Blue-tailed Ischnura pumilio in Carmarthenshire The Conservation of the Scarce Blue-tailed Damselfly Ischnura pumilio in Carmarthenshire.

UK distribution

Fig 1 shows the UK distribution of I.pumilio. It occurs at scattered sites across southern Britain and Ireland. The highest density of sites occurs in South West Wales, Devon and Cornwall, and the New Forest.

Figure 1 – UK distribution (Cham 2004)

Colony sizes are very variable, casual observation giving adult counts ranging from a few to as many as 100. Taverner(2004) sights a count of 70, which he describes as very high for Hampshire. Chan(1993) recounts a casual count equated to a mark-recapture count of 40 on the same day with a total count for the whole season of 628 individuals. Colonies are also quite transient; indeed Lucus(1900) considered it to be extinct in Britain as there had been no records for several years (although he acknowledged that difficulties with identification and small size of colonies probably resulted in it being overlooked and ‘therefore still with us’).

The trasient nature of colonies means that estimates of its population within the UK are difficult to make. Although from the UK distribution map Devon seems to be a strong hold, Smallshire (1995) indicates that it occurred in only 6 sites at that time. It may well be that this damselfly has the smallest UK population of all the long-term resident species of .

Figure 2 – Carmarthenshire distribution Carmarthenshire distribution

Figure 2 shows the extent of records for Carmarthenshire. No systematic assessment of the species has been carried out in Carmarthenshire, the existing distribution information resulting from casual observation occurring in general odonata surveys.

I.pumilio has been recorded over most of Carmarthenshre. It can therefore be considered widespread. It is even common at some sites on some occasions. This is, however, nowhere near the true situation.

This has ability to both exploit habitats which occur widely (but occurring only for a few years before natural succession makes them unsuitable) and apparently to be highly dispersive. It seems more likely that there are a small number of permanent colonies in West Wales that disperse over the Carmarthenshire to exploit suitable habitat provided by the construction of new ponds.

Within Carmarthenshire I.pumilio exploits two types of habitats 1. Newly created ponds and 2. Slow/very slow flowing streams/flushes with soft organic substrates with little or no submerged vegetation.

The element that is common to both these habitats is shallow water with little vegetation. This can warm up rapidly in summer (many of the spring fed flushes may also remain ice-free in all but the coldest winters). The life cycle of I.pumilio is completed within one year and there is evidence that larval development occurs during the winter, which is critical to its successful completion (Cham 1995). Such habitats are not often shared with other odonata (and other invertebrates) and this lack of competition may also be attractive.

Ponds. Ponds in which I.pumilio has been recorded vary widely. At one site of the two ponds that supported the damselfly, one was a concrete lined garden pond 3x5m, 300 to 600mm deep; the other being a 10x10m, 150 to 1000mm deep clay lined pond. The former had the damselfly from new in 1984 to about 1992, whilst the latter supported it, again from new in 1992 to 1997. Many farm reservoirs in the few years following their construction are often attractive to I.pumilio in Carmarthenshire. Unfortunately they soon become vegetated and occupied by other odonata and invertebrates becoming unsuitable.

Streams and flushes. Again, these habitats can be quite variable, but all have very slow water flows with deep soft substrates with areas of little or no vegetation. Often only short lengths are suitable, local factors forming wide channels with about 150mm deep water on shallow gradients with waterflows so slow they are almost imperceptible.

Ischnura pumilio sites The Carmarthenshire distribution map shows no squares where I.pumilio has been recorded continuously over a thirty-year period, but there are a few elsewhere in West Wales. These ‘Permanent Sites’ in Pembrokeshire can be found on the lower slopes of the Preseli Hills, on streams forming the natural drainage system modified by movements and grazing, Where pinch points channel and concentrate animal movements across streams the soft open conditions required by I.pumilio are maintained.

Most of the Carmarthenshire sites are ponds where I.pumilio has established temporary colonies (‘Temporary Sites’). These probably allow I.pumilio to maintain an itinerant population but is dependant on the continuous availability of new ponds. Below are some of these sites.

Conservation

‘Permanent Sites’ creation

Given the ease with which such sites may be created it would be entirely feasible to develop a network of such sites across the county. Appendix 1 gives a description of the requirements of such sites. Without disturbance provided by animal movements these sites will quickly develop through the early successional stages ideal for I.pumilio. Continuity of availability of suitable is therefore a major criteria in site selection and perhaps also a limiting factor on ‘Permanent Site’ creation. Hence plans and funding for the development of ‘Permanent Sites’ must make provision for adequate stock and stock management infrastructure (fences, extra gates etc).

Appendix 1 – Creation of an Ischnura pumilio flush A suitable site must have a small permanent unpolluted stream, be relatively flat and be grazed by stock. The streambed should be of sufficient width to allow most flows through at very slow currents; at normal dry weather flow the current should be imperceptible. The stream banks should be very low so that under flood conditions overtopping quickly occurs. There should be sufficient flat areas either side of the stream to accommodate such flows. The depth of the water above a soft bottom should be maintained at between 100 to 300mm by a flow restriction down stream of the site. The length of the site needs to be a minimum of 5m but can be as long as practicable. The ideal position would be between grazing fields. There must be some movements of animals along the stream, sufficient to restrict the development of submerged vegetation so that large areas of the stream bed remain visible.

Figure 3 shows what such a site would look like. The layout of grazing areas around the site forces animals to cross the water to move between them. These movements are sufficient to maintain the required condition, the areas of clear water support no submerged vegetation. The view is downstream, the stream has a restricted channel at its end outside the grazing fields.

Figure 4 shows a smaller site formed across the gradient of the slope. Here the outlet (in the foreground) is both physically restricted and clogged with vegetation. Again the clear water supports no submerged vegetation. Although the depth of clear water is about 150mm the depth to solid ground is 300mm.

There is no need to restrict development at a site to just one such pool, but a series could be created. The use of fences and gates providing alternative animal routes could be used to regulate animal movements to maintain optimal conditions.

As can be seen from both figures emergent vegetation along the stream edges and shelter provided by surrounding gorse could well increase the site’s attractiveness to I.pumilio.

It would also be possible to create pools, using disturbance (by animals or vehicles?) to maintain the correct conditions, that may prove to be equally attractive to I.pumilio.

References. Cham(1993):Steve Cham – Further observation on generation time and maturation of Ischnura pumilio with notes on a mark-recapture programme. Journal of the British Dragonfly Society 9:40-46 Cham(1995):Steve Cham – The Scarce Blue-tailed Damselfly – the conservation of a wandering opportunist. British Wildlife 7:220-225 Cham(2004):Steve Cham – Dragonflies of Bedfordshire. Lucus(1900):Lucus, W.J. – British Dragonflies. Smallshire(1995):Smallshire, D – An Inventory of the key dragonfly sites in Devon. Taverner(2004):John Taverner, Steve Cham and Alan Hold – The Dragonflies of Hampshire.