The UK translocation programme

The need for translocation

D. plantarius is intrinsically very vulnerable to extinction because it is restricted to only three sites, at one of which its popoulation is extremely small. Its Species Action Plan, first produced in 1999 and revised in 2005 and 2008, seeks to address this issue with the following ambitious targets for its future status:

  • an increase the overall range of D. plantarius at Redgrave & Lopham Fen to 13 Ha of habitat occupied 3 years in 5 by 2010 and to 65 Ha by 2020
  • the number of sites with sustainable populations of D. plantarius should be increased by six by 2010. By 2020 the total number of sites with sustainable populations should be increased to 12.

Despite the slight increase in range at Redgrave and Lopham Fen since 2006 it has become clear that both of these targets will have to be met by deliberate translocation to new sites - both within the Redgrave and Lopham Fen nature reserve complex and more widely in both East Anglia and Southern England. Research evidence (i) that D. plantarius has a low propensity to disperse (Pearson 2008) and (ii) that there has been a significant decline in genetic diversity in the Redgrave and Lopham Fen population since 1992, suggests that establishment of new populations is likely to be essential to ensure the long-term future of this species in the UK. Natural England, the lead organisation for the Action Plan for this species, committed themselves to a translocation programme if it could be established  that it could satisfactorily meet the criteria for translocation laid down in guidelines produced by the IUCN, JNCC and Invertebrate Link.

Preparation for the translocation programme

During 2008 and 2009 British Arachnological Society experts surveyed potentially suitable habitat to ensure that our current understanding of the UK distribution of D. plantarius was correct and that major populations were unlikely to have been overlooked or misidentified. Their work was augmented by  appeals for Dolomedes sightings through articles in specialist magazines, an identification card issued to those working in the wetlands of the Norfolk and Suffolk Broads, and through this website. New populations of Dolomedes fimbriatus but not of D. plantarius were discovered. 

Over the same period,  techniques for rearing newly-hatched D. plantarius in captivity were tested at the John Innes Centre Insectory, Norwich. Because the D. plantarius population at Redgrave and Lopham fen is so small, removal of spiders for translocation is not viable. However, this work, and subsequent captive rearing trials, has shown that capture of adults females with egg sacs, and rearing of their progeny for the first few months of life, can achieve very high survival rates over a period when survival in the wild is almost certainly very low. The source population can than be reinforced at the same time as a new population is established, by the release of both a proportion of the reared spiderlings and of the captive adult females when they produce second broods. Successful production of second broods in the wild is rare in the Redgrave and Lopham Fen population but much commoner amongst captive females. Return of the females to the wild just after their brood emerges from the egg sac decreases the probability of both mother and egg sac succumbing to predation.

In spring 2010 a Steering Group convened by Natural England reviewed the case for translocation and concluded that translocations of D. plantarius should go ahead in England subject to establishing the most appropriate provenance of stock for new populations. As yet, there is no translocation programme in Wales, where CCW wish to undertake more survey work before making any decision on whether translocation is necessary or appropriate.

An experimental approach was taken to determining the most appropriate provenance of D. plantarius for use at new sites - from one or other of the two English populations, or from both sites. Although combining these two long-isolated populations to increase genetic diversity by might be expected to result in offspring better able to adapt to their new environment and to future environmental change (hybrid vigour), there are circumstances in which such hybrids can be less successful (outbreeding depression). To ensure that populations established by deliberate translocation would stand the best possible chance of long-term success, an experiment was undertaken in 2010 to compare courtship and mating behaviour, fecundity, and survival and growth of progeny in crosses between and within the two English D. plantarius populations. Sub-adult spiders collected under license from the Sussex Wildlife Trust's nature reserve on the Pevensey Levels and the Suffolk Wildlife Trust's Redgrave & Lopham Fen nature reserve were matured in captivity. Once adult, within and between population matings were set up in an artificial arena in which all aspects of courtship behaviour could be observed and recorded. Fecundity, and the growth and survival of the resulting progeny over a 15 week period, were measured . No mating barriers between the populations were detected and subsequent rearing of the resulting offspring - from 18 successful parings - showed that the hybrids were as successful as the within-populations crosses.

Translocations in 2010

Because of this positive result, all of the spiderlings produced by this experiment were used to establish the UK's first new populations of this species, in October 2010. The Steering Group for the project approved release of both the hybrid spiderlings, and those of Pevensey Levels origin, at the Suffolk Wildlife Trust's Castle Marshes reserve. This internationally important area of grazing marshes is on the River Waveney, downstream from Redgrave and Lopham Fen at the source of the river. It is highly likely that this species occurred in this area in the past but was lost when the quality of the ditches was degraded by conversion of the marshes to arable agriculture. The ditches have now been restored and support a rich assemblage of invertebrates and plants, very similar to those on the Pevensey Levels, the spider's stronghold on the south coast of England. The area is, in many respects, very much more similar to the Pevensey Levels than to Redgrave and Lopham Fen.

In addition to releasing around 2800 spiderlings at Castle Marshes, over 1900 spiderlings of single-site provenance were returned to their natal populations on the the Pevensey Levels and at Redgrave and Lopham Fen. At the latter site they were used not only to boost numbers in the two small areas to which they had become confined, but also to create a new, third focus for the population within the nature reserve. Although habitat restoration by the Suffolk Wildlife Trust at this site over the last decade has been very successful, the spiders have failed to recolonise ideal new areas. Translocating them within the reserve, in addition to creating chains of new turf ponds and scrapes linking the sub-populations, is expected to aid recolonisation of extensive areas of the reserve. In future years, the possibility of boosting depleted genetic diversity at Redgrave and Lopham Fen by introducing spiders from the Pevensey Levels will be evaluated.

To create a natural age-structure in the new populations, a further release of spiderlings would be needed in 2011. Monitoring of the new populations will be used to inform an annual review and modification of the translocation programme. Monitoring will involve not only provide measures of the sizes of the populations but also of their changing genetic makeup. Losses of introduced haplotypes from the new populations will be used to assess which elements of the parental stock are most successful in the new sites. This will also provide a guide to the need to augment the new populations with additional stock.
 
Spider-rearing in a Suffolk kitchen....
UK media attention was briefly diverted from the gloom of the UK Government's Comprehensive Spending Review in October 2010 by the story of the spiderling releases at Castle Marshes and Redgrave and Lopham Fen. National as well as local radio channels and newspapers picked up this good news story in the International Year of Biodiversity. The fact that the spiderlings parents had been mated, and most of the spiderlings hatched and reared in a domestic kitchen added human interest to the story! Although some of the spiderlings were reared in a conventional laboratory setting at the Insectory at the John Innes Centre in Norwich most lived in my kitchen where they were reared them individual test tubes (to avoid cannibalism) and fed them on an abundant supply of fruitflies from the garden compost bins and lesser dung flies, netted from fresh pony dung!
The news story travelled around the world, not only via the BBC and national newspaper websites, but also reaching newspapers from Iceland, to the Netherlands and the USA. It's good to know that small spiders can make big news! Click on the links to read the Press releases issued by and the
Suffolk Wildlife Trust.
View coverage on the BBC website.
Read some of the newspaper coverage of the story:
The Daily Telegraph
The Guardian
The Daily Mail
The East Anglian Daily Times
The Eastern Daily Press
The Diss Mercury
The Diss Express
The Lowestoft Journal
and from Iceland...
Posted 11-2010 

Translocation in 2011 

The D. plantarius translocation programme continued in East Anglia in 2011 with the establishment of a further new population at Suffolk Wildlife Trust's Calton Marshes reserve on the lower Waveney and a second new focus of population at Redgrave & Lopham Fen. In addition, as the planned, a second introduction of spiderlings was made to the 2010 sites.  Mixed Redgrave & Lopham Fen and Pevensey Levels provenance was, once again, used at the lower Waveney sites while only local provenance was used within Redgrave & Lopham Fen.  

In 2011 the spiderlings used for the releases were the progeny of gravid, wild caught females. Those from the small Redgrave & Lopham Fen population were once again reared in captivity for three months, ensuring high survival rates, before release in the autumn. Their mothers were retained in captivity until their second broods hatched and were then released back at their site of cature to augment their natal population.  In contrast to 2010, the adult females from the much larger Pevensey Levels population were not returned to their natal areas but were released, together with their first nurseries, at the new release sites in July and August. These females built their nursery webs in aquaria made from 5l plastic water bottles. Once the spiderlings were ca one week old - the age at which they would normally start to disperse from the nursery - the 'bottled' nurseries, together with their guarding mothers, were taken to their new homes. They were anchored in suitable vegetation and openend to allow the spiders to escape. Several of the mothers of these broods went on to produce successful second broods in their new homes.

Another new departure for 2011 was the very welcome help of four UK zoos, all members of the British & Irish Association of Zoos and Aquaria  (BIAZA), in rearing the Redgrave & Lopham Fen test tubes spiderlings. Ian Hughes of Dudley Zoo, Karen Entwhistle of Chester Zoo, Keith Russell of Chessington World of Adventure and Caroline Howard of Lakeland Wildlife Oasis all became foster parents to many tiny spiderlings and suffered all longs hours, anxieties and rewards of this very unusual job! This new partnership of BIAZA zoos with the D. plantarius translocation programme brings huge benefits in terms not only of the numbers of spiderlings that can be reared but also in expertise in developing the captive rearing methods. As the partnership develops, it will bring opportunities to raise public awareness of the plight of this species, and its wetland habitats, to a huge new audience.