The invertebrates of Prosperous Bay Plain, St Helena a survey by Philip and Myrtle Ashmole September – December 2003 Commissioned by the St Helena Government and financed by the Foreign and Commonwealth Office

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Foreign & Commonwealth Office, St Helena Government, Department for International Development, Joint Nature Conservation Committee, St Helena UK Representative, Atkins (Access Feasibility Study Consultants), UK Overseas Territories Conservation Forum, South Atlantic Working Group, St Helena National Trust, Zoological Society of London, Natural History Museum, Buglife.

Plate 6. Views of Prosperous Bay Plain.

1. Background and organisation of the project

    • 1.1. Introduction

A proposal to build an airport at St Helena has been under consideration for many years and Prosperous Bay Plain has always been one of the obvious possible sites. Unfortunately, however, this area is of very special biological significance. It represents the only ancient desert ecosystem on St Helena, has changed relatively little since the arrival of humans on the island, and is the only known site of occurrence of some 20 endemic species and five endemic genera of invertebrate animals.

The relevant authorities have a clear obligation to care for such an environment in territory that they control. For St Helena this obligation is made explicit by the Environment Charter, established in September 2003 by the Governments of St Helena and the UK. It committed the parties to ten Guiding Principles, of which four are especially relevant to the Prosperous Bay Plain airport proposal:
3. To identify environmental opportunities, costs and risks in all policies and strategies.
4. To seek expert advice and consult openly with interested parties on decisions affecting the environment.
5. To aim for solutions which benefit both the environment and development.
10. To study and celebrate our environmental heritage as a treasure to share with our children.
It was in the context of this commitment that in 2003 the Government of St Helena and the UK Foreign & Commonwealth Office arranged for an intensive survey of the invertebrate community of Prosperous Bay Plain (PBP) and the immediately surrounding area. The work of the Belgian entomologists in the 1960s, analysed by Ashmole & Ashmole (2000: 116-118) had demonstrated the high diversity of endemic invertebrates on PBP. The aim of the 2003 survey was to find out whether the bulk of the species previously recorded from the plain are still present there, to assess the likely impact of airport construction on their populations, and to suggest appropriate initiatives in damage limitation and mitigation.
The potential threat to the PBP area from airport construction has raised concern among conservationists, who recognise the need for an airport on St Helena but feel strongly that appropriate action must be taken to protect the endemic fauna. Environmental considerations relating to airport development were highlighted by Spooner (2000).
At the time of writing, the access consultants Atkins have apparently completed their Access Feasibility Study, but the full text of the report is not publicly available. However, the Atkins (undated) public information document ‘St Helena Access Feasibility Study: Access Options Paper’ includes ‘Environment’ among the Assessment Criteria in Appendix E. The sub-criteria under Environment are:

  • Impact of construction of option (least is best)

  • Impact of access arrangement (least is best)

  • Impact of operation of option (least is best)

  • Impact of resulting economic and social development (least is best)

  • Even though the option may lead to some permanent loss of habitat for endemic species, is it likely to adversely affect the sustainability of the species on the island? (least is best)

Within the main document and in Appendix F there is consideration of the weighting of the various assessment criteria, and it is clear that the weight given to Environment by both SHG and HMG is low (see table in Appendix F). However, both On-island and Off-island Saints (and Atkins) weight Environment more heavily. We are somewhat surprised by the government view, since our personal belief is that the future of tourist development on St Helena will depend heavily on the perceived quality of the island environment and on publicity relating to this.

We guess, however, that a somewhat higher weighting for Environment would not significantly affect the ranking of the access options. Of much greater importance will be the vigour with which environmental impacts are monitored, controlled and mitigated if the chosen option is one of those involving airport development.

    • 1.2. Terms of reference

The project objective was:

“To determine the location, habitat status and ecology of the endemic invertebrate fauna present in the Prosperous Bay Plain area”.
Proposed outcomes in fulfilling this objective were:
Mapping of habitats on Prosperous Bay Plain

Collation of baseline data on invertebrates

Study of status and ecology of the species found

Production of a guide to the fauna of the area

Identification of measures to mitigate any damage caused by airport development

Provision of training of local staff in invertebrate survey and identification techniques

    • 1.3. Personnel

Philip and Myrtle Ashmole were chosen to undertake this project because of their extensive knowledge of the natural history of St Helena and their experience in surveying the invertebrate faunas of habitats on volcanic islands. Their interest in St Helena stemmed primarily from long-term work on the origin, evolution and ecology of the animal communities of oceanic islands.

The Ashmoles spent six months on St Helena in 1994-1995, studying the island’s flora and fauna in general and undertaking research on invertebrates. The visit led to publication of their book St Helena and Ascension Island: a natural history, published by Anthony Nelson (2000) with financial support from the FCO. It is now distributed from Both have degrees in zoology, and Philip also has a doctorate in tropical seabird ecology, based on work on Ascension Island. Philip has previously taught ornithology, zoology, ecology and evolution at Yale and Edinburgh Universities. Both he and Myrtle have undertaken research on many other oceanic islands including the Azores, Hawaii and Galapagos. One of their relevant scientific papers (Ashmole & Ashmole 1997) was an analysis of the whole terrestrial fauna of Ascension Island, written after their work in caves and on lava flows there demonstrated the presence of many more endemic invertebrates than had previously been recognised. They have helped to develop proposals for ecological restoration on both Ascension Island and St Helena.

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