Cave management in Mauritius

Greg Middleton

ACKMA Journal No 36, September 1999, pp 3-10

Mauritius is a nation of just over a million people inhabiting two small islands in the western Indian Ocean 850 km east of Madagascar. The main island is 1825 sq km (one thirty-fifth the size of Tasmania) and the second island, Rodrigues, 560 km further to the north-east (Australia's nearest neighbour to the west!), is just 110 sq km.

Both islands are volcanic in origin, as is the more westerly Reunion, which still enjoys an active volcano. On Mauritius the last volcanic activity was about 26,000 years ago (Antoine 1983) and most of the caves formed before then in rapidly-flowing low silica lavas. There are some small patches of calcareous aeolianite and a few small offshore islands are entirely composed of this recent limestone. On Rodrigues it occupies a significant part of the south-west of the island (Halliday and Middleton 1996) and hosts all its major caves, including the country's only show cave.

I worked in Mauritius from 1991 to 1995, setting up the country's first National Park in the Black River Gorges and spending my spare time exploring and documenting its lava and karst caves (see Middleton 1994a, b, etc). During that time I became aware that there were a lot more caves in Mauritius than most people realised, that their value was not generally appreciated by the populous and they were under threat from various sources.

The first systematic speleological fieldwork to be done in Mauritius was in April 1991 by a group of French cavers under François Billon. They surveyed at least 12 caves (totalling over 2.4 km), including two on Rodrigues, and prepared a comprehensive report on their findings (Billon et al. 1991; Billon & Chojnacki 1993). They drew attention to the dumping of rubbish in caves, the need for public education and regulations, the possibility of tourist development (suggesting Petite Rivière Cave or Pont Bondieu) and proposed the formation of an "association de spéléologie".

Clement Moutou, who had guided the French team, took up the latter proposal and formed the Spéléo-Club de l'Océan Indien which existed from 1992 to 1994, but never had more than a handful of members. Through this group the author was introduced to a number of Mauritian lava caves and met Jörg and Roselyne Hauchler who were to be invaluable in the further exploration and documentation of the caves. Billon's group hoped to get funding from the Mauritian government to further its work but this was never forthcoming.

During return visits to Mauritius in 1996 and 1997 I explored further caves with Jörg and two rangers from the National Park, Mario Allet and Paul Moolee. In July 1995 I had met Prem Saddul, Head of the Dept. of Social Sciences at the Institute of Education, who had just published a detailed analysis of the island's landforms (Saddul 1995) which included reference to various lava caves. With his encouragement I prepared a proposal for a project to document the caves, assess their values and make proposals for their future management and conservation. This was presented to the Minister for Environment in 1996 but it was not until July 1998 that the project actually commenced.

Previous management/conservation efforts

There had been about four earlier attempts to protect or present Mauritian caves: Caverne Patates, Pont Bondieu, Petite Rivière Cave and Palma Lava Cave.

The most notable of these is the on-going use of Caverne Patate, a l km+ karst cave on Rodrigues, as a show cave. The caves of Rodrigues first came to the notice of the scientific world in the 1780s when they provided happy hunting-grounds for seekers of bones of extinct birds - in this case the solitaire (Pezophaps solitarius) which became extinct by 1760 (North-Coombes 1971; Middleton, 1995). Many early visits are recorded and much damage was done (both by 'scientists' and visiting vandals) but at some point the locals realised that in Caverne Patate they had a tourism asset which people would pay to visit. By 1995 when the author first visited it (Middleton 1996), this cave had suffered over 200 years of visitors using flaming kerosene torches and every horizontal surface now carries a generous deposit of carbon. Very few speleothems within reach survive. Fortunately the Australian Government, in 1991, donated the first rechargeable electric torches and since then kerosene torches have not been used, save for the occasional re-enactment. There are two guides, Benjamin and Ernest, who, with Creole and a little French, provide the most basic tours of the 'old' kind, pointing out fantasy figures and recounting tales of passages extending to, or under, the sea. They are not allowed to collect money so the tourist must buy a permit to enter the cave at the island's administration office, 15 km away in Port Mathurin. Bad luck for the tourist who does not book through a hotel or travel agent. The permit admits up to ten visitors so it provides no record of how many people actually visit the cave each year. The tours last about an hour, depending how many are in the party and how much they chat with the guide. The cave is spacious and the floor close to level so it is not a difficult tour and almost no 'improvements' have been necessary to provide access. In fact the only structure is the flight of calcarenite steps at the end of the tour. Apart from those near the top, these have seen better days and are in urgent need of reconstruction. During the cyclone season (December-March) when there are heavy rains the lowest parts of the cave fill with water and it is often closed to visitors for up to two months. A solution is being sought for this problem.

Pont Bondieu is a large arch, or a short, wide lava tunnel (80m long x 35m wide x 15m high), crossed by a minor road in the Nouvelle Decouverte district of the main island. Because it's entry pit is so convenient to the road it has been a convenient dumping site for many years. It houses quite large bat and cave swiftlet populations which the Wildlife Clubs of Mauritius sought to protect around 1990 by erecting a sign and clearing a pathway through the accumulated mountain of old tyres, household, industrial and medical waste. The sign was pulled up and thrown into the pit and rubbish dumping continued. The Department of Environment then stepped in, built a sturdy fence along the road on the edge of the pit and a flight of stone steps the 20m or so to the bottom and moved more of the rubbish. In April 1994 the cave was 'opened' and handed over to local youth groups to look after. Part of the fence has since been removed but rubbish dumping does not seem to have recommenced and, despite the easier access for would-be nest robbers, the cave swiftlet colony is surviving.

Petite Rivière Lava Cave is the oldest known and most frequently written-about cave on the main island. It was surveyed by one Marquis d'Albergati before 1769. He calculated the total length as 342 and one third (French) fathoms, equal to 667.2m, but unfortunately he did not draw a plan. In 1773 Bernardin de Saint-Pierre published his data and an account of a visit to the cave. In 1830 a somewhat fanciful and grossly exaggerated drawing of the entrance became the first published illustration of a Mauritian cave (Dumont D'Urville 1830). In 1991 a British ornithologist, Roger Safford, became sufficiently concerned about the depredations made on the cave's swiftlets by local nest robbers, that he convinced the owners of the land, Medine Sugar Estate, to build a large steel grille across the cave just inside the entrance (Safford 1993). Sadly, this has been broken down, even to the point of using explosives on the gate (Hauchler, pers. comm.) each time the owners have repaired it. Although the culprits may be those seeking swiftlet nests, as Saffort observed, the cave also contains an altar used for black magic and it may be its practitioners who are so determined to retain access.

In June 1994 the owners of la Caverne de Palma, a significant swiftlet and bat breeding cave near the centre of the main island, were constrained in the nick of time by officers of the Department of Environment as a bulldozer pushed rubble into the entry pit to prepare the site for housing development. The owner was persuaded to desist and ultimately entered into a management arrangement with the Department, under which it erected a security fence around the pit to try to prevent filling and nest-robbing. Like the Petite Rivière gate, that at Palma has been broken open. The Department has done nothing to maintain the site and a house has been built within 20 metres, but at least the entrance remains open.

The Caves of Mauritius Project 1998

It was against this background of ad hoc activity and lack of follow-up that the author entered into a contract with the Permanent Secretary of the Ministry of Local Government and Environment in July 1998 to:

undertake a comprehensive study of as many as possible of the caves, pipes and lava tunnels of Mauritius and Rodrigues and prepare or obtain surveys of each and compile an inventory of their significant features including location, ownership, biological content, history, current use. Make a photographic record of notable features.

The second phase was to:

prepare an assessment of each cave in terms of its specific values and potential uses (such as for conservation, recreation, science, education, tourism, water supply, etc) and determine the optimum use for each cave.

And finally:

prepare recommendations on the future use and management of each cave, including preservation, as appropriate. Report also on the need for a specific Act for the protection of caves and their contents, and for the conduct of education and publicity campaigns in relation to caves and their conservation.

The contract provided for me to be assisted by Jörg Hauchler, the former member of the Spéléo-Club who was prepared to devote three days a week to the project for little more than his expenses and a field officer of the National Parks and Conservation Service - though this was never actually arranged. A volunteer, Imran Vencapah, made up for this deficiency during the first month. The author was provided with an office at the National Environmental Laboratories, a computer and a 4x4 vehicle.

The project was originally designed for four months but eventually took five. At first we were concerned about how we might find new caves and we contemplated newspaper advertisements. As it turned out, just examining maps and asking a few people produced more leads than we could handle and reluctantly we eventually had to stop looking. As well as searching for caves we talked to some land owners and managers about their caves and their values and, in some cases, took them to inspect particular caves. For each day we spent in the field I had to spend at least a day reducing the survey data, drawing up the results and attending to bureaucratic matters. The details of the exploratory work are spelt out elsewhere (Middleton, in press); the state of knowledge by the end of the project (December 1998) is summarised in Table 1.

Table 1 - Documented caves of Mauritius by Region and Area

RegionArea# entrances# cavesTotal length (m)
North-WestGoodlands32355
North-EastPlaine des Roches46223,520
Central WestMoka Range114.2
 Plaine St Pierre1191,115
 Plaine Wilhems22121,160
Central EastBeau Champ2214
 Nouvelle Decouverte39263,509
 Quartier Militaire77749
 Trou d'Eau Douce3263
South-WestBassin Blanc1180
 Chamarel Falls66109
 Kanaka1310725
 La Prairie*3296
 Mont Blanc97754
South-eastGrand Port*33115
 Ile aux Aigrette*2135
 Plaine Magnien1185
 Rose Belle2268
 Savannah44500
RodriguesCorail-Petite Butte*971,757
 Plaine Caverne*1910235
 TOTAL20914016,501

*Caves formed in calcarenite (karst).

Some immediate results of the study

While we found that many people knew of cave entrances, they had almost never entered the caves and we found ignorance of what lies beneath their feet to be virtually universal among owners and managers of the land. In one case, at Nouvelle Decouverte, we were able to influence a landowner (Nazeer Rosebally) not to fill in a small and insignificant-looking hole (ND21) which led to an interesting and complex system 360m in extent. We also suggested that it was not wise to drive the bulldozer over the area where the cave lay just a couple of metres below the surface. Although he told us of another entrance on his property which he had blocked with large rocks (apparently for fear of children getting into it) we were unable to convince him to reopen it.

In the case of the Mont Ida caves, on FUEL Sugar Estate land, we were able to take the company's agronomist, Dominique Rousset, on a tour of the caves and point out the very unstable nature of the roof above chambers up to seven metres high and 15 metres wide. He agreed that it would be most unwise to employ heavy machinery above this cave and as they had lost a dozer into such a collapse a couple of years before it is likely they will heed this advice.

During the project 'Clean up the World Day' (an Australian initiative embraced by Mauritius a couple of years before) was to be celebrated in Mauritius. Demonstration projects were to be carried out across the island, initiated by the Dept. of Environment but involving local people. It was felt that one or two caves should be included and we were asked to nominate some which would benefit from being 'cleaned'. While it is not hard to identify caves filled with rubbish in Mauritius, some contain so much that a couple of days work would not achieve a result, while one would be reluctant to focus public attention on others. In a couple of cases rubbish even provides a measure of protection for nest sites as it discourages nest robbers from entering. Two possible sites were, nevertheless, identified: Glen Park Cave (especially PW5), Plaines Wilhelms, and Caverne Trois Bras, Goodlands. In the former case the owner refused to cooperate with the department but at Trois Bras the owner, Hoodith Ramphul, agreed to give the cave, including a small area around the entrance which was to be fenced, to the department. This was officially handed over at a ceremony in the dramatically cleaned cave entrance on 20 September 1998 when the Minister, the Hon. James Butty David, accompanied by the Australian High Commissioner, Mr Chris Marchant, inspected the cave. During field work at the cave we learned from local people that up until about 25 years ago it had served as a Hindu religious shrine or kalimye. A single clay vessel remained at the site in the most northerly chamber at the time of the community clean-up.

Near a government sheep breeding station at Salazie in the Nouvelle Decouverte area we were shown a cave (ND 11-12-13) which had unfortunately been used to dispose of innumerable sheep carcases. We arranged for a letter to be sent to the Ministry of Agriculture pointing out that this was not a desirable practice; it is probably illegal under environmental legislation; we hope it has ceased. We found a worse case at PR40, near Roches Noires, where a cow had only days before been dumped into a shallow entrance hole. The smell was horrendous and caused us to take nearly three months to complete surveying of the cave (which reached 810m in length). We tried to get the Department of Environment to remove the carcass but to no avail; a small quantity of lime was thrown in the hole. No attempt was made to find the guilty party. When we were eventually able to approach the site from below (the cave has ten entrances) we discovered that this particular hole had been used for many years as a disposal site for dead cattle - the chamber below was a veritable cattle charnel-house.

Also in Roches Noires was a cave containing fresh water right in the main street. It had traditionally been used by the women of the village for washing but the land had been bought by a developer and there were fears that access to the cave would be cut off. We advocated the negotiation of a management agreement with the owner to protect the site and retain free access.

At Camp Thorel we were able to extend the main cave (surveyed to 612m by Billon et al in 1991) to 1,015m - the longest lava cave - but we also noted the foul smells present in parts of the cave and, by linking in surface surveys, were able to identify the pit toilets which were the cause of the problem. Although this is probably the most interesting and challenging cave in the country, visiting it certainly constitutes a health hazard. Restoration of the cave could only be brought about by moving the village or at least providing a piped sewerage system, neither of which is likely in the near future.

In Mangapoule Lava Cave in the Quartier Militaire district we found some of the most interesting invertebrate fauna living in a muddy lava tube which periodically fills with water. The cave takes the run-off from surrounding fields and is rapidly filling with fine topsoil. Stabilisation of the catchment could arrest this but such a measure would inevitably result in reduced production from the affected area and is unlikely to occur.

Proposals for future management and conservation of caves

In the hope of maximising the chance of achieving some concrete results from the project I kept the major recommendations to four. They were:

  1. The creation of a "Plaine des Roches Lava Caves National Park" encompassing a series of significant caves in the Plaine des Roches area.
  2. The creation of a "Rodrigues Karst National Park" to include most of the significant caves and dry valleys in the Corail Petite-Butte, Plaine Caverne and Plaine Corail areas of south-west Rodrigues.
  3. The priority for funding should be for the cleaning and rehabilitation of Caverne Patate in Rodrigues and, when funds permit, the lighting of the cave with electricity.
  4. Other significant caves should either be reserved for conservation and low-key recreation purposes, or made the subject of management agreements between the appropriate agency of Government and the respective landowner.

Implementation Problems

A major problem with implementation of the two national park proposals, as observed by the Director of Environment at the handing over of the project report in Port Louis on 22 December 1998, is that national parks are the responsibility of another ministry (currently Agriculture, Fisheries and Cooperatives). Six months later it is not clear whether a copy of the report has been provided to the responsible ministry.

A major difficulty for the Plaine des Roches proposal may be the long-standing plan for a second international airport to be built in this region, despite the fact that there seems to be no justification whatever for seriously considering a second airport on this small island. The land is extremely poor, currently supporting eucalypts grown for scaffolding material, weeds and scrub. Part of this proposal is a proposal to further investigate the possibility of opening "Twilight Cavern" (PR18-30-31) as a show cave with guided tours. The cave is large in cross-section and over 500m long; there is also a good possibility that excavation of the collapse at the eastern end could open up significant (virgin) passage, making the cave even more interesting. If the government is not interested in opening this cave it would be essential to find a sympathetic entrepeneur who would be prepared to develop it sympathetically, taking full account of ecological considerations.

By coincidence the Karst National Park proposal for SW Rodrigues is also threatened by an airport - in this case extension of the Plaine Corail airport runway to enable larger planes to service the island. The proposal for a national park on Rodrigues is further complicated by the fact that the island is administered by the Ministry of Rodrigues and the Ministry of Agriculture has very little business (and even less acceptance) there. However, again, the area proposed for reservation is very barren and not productive - currently it seems to support only a couple of flocks of goats. Part of the area is already fenced off as the Anse Quitor Nature Reserve and it contains a number of rare plants.

The difficulties for the Caverne Patate rehabilitation project are (1) it is on the remote island of Rodrigues, (2) there may be problems deciding which Ministry should fund any work (Environment, Agriculture, Rodrigues or Tourism), (3) there may be no funding allocation for it and (4) there is no one in Mauritius with any experience cleaning caves so someone will need to be brought in from overseas - and that can be a very protracted process.

References

Antoine, R. 1983 La dernière coulée de laves à l'île Maurice. Rev. agric. et sucr., 62(2):91-92.

Billon, François, Chojnacki, Phillipe, Billon, Catherine & Rousseau, Ghislaine 1991 Explorations souterraines à L'Ile Maurice: Compte rendu expédition Avril 1991. Spéléo-Club Nivernibou: Decize, France 46 pp.

Billon, François & Chojnacki, Phillipe 1993 Explorations souterraines a L'Île Maurice. Sous le Plancher, #8:67-86.

Dumont D'Urville, J.S.C. le Comte 1830 Voyage de la corvette l'Astrolabe. Exécuté par ordre du Roi, pendant les annèes 1826-29 sous le commandement de M. J. Dumont D'Urville, Capitaine de Vaisseau. J. Tastu: Paris, 'Atlas' vol. 2, pl. 243.

Halliday, William R. & Middleton, Gregory 1996 A subdued karst on the island of Rodrigues, Mauritius [in] Fornós, Joan-J. & Ginés, Angel (Eds.) Karren Landforms. Universitat de les Ines Balears: Palma de Mallorca. pp.345-354.

Middleton, Greg 1994a Rambles under Mauritius #1 - Petite Rivière. J. Sydney Speleol. Soc., 38(8) : 131-133.

Middleton, Greg 1994b Rambles under Mauritius #2 - Chemin Grenier: Outings by the SpéléoClub de L'Océan Indien, 9 & 23 May 1993 J. Sydney Speleol. Soc., 38(9):149-150.

Middleton, Greg 1995 Early accounts of caves in Mauritius. Helictite, 33(1):5-18

Middleton, Greg 1996 Rambles under Mauritius #7 - Plaine Coral', Rodrigues. J. Sydney Speleol. Soc., 40(6):83-94

Middleton, Greg in press The Caves of Mauritius Project 1998: Part 1 - exploration and documentation. J. Sydney Speleol. Soc.

North-Coombes, A. 1971 The Island of Rodrigues. The Author and Mauritius Advertising Bureau:Port Louis. pp. 259-270 [Extracts reprinted 1991 in J. Sydney Speleol. Soc., 35(9):171-175.]

Safford, Roger (1993) Conservation of the Mascarene Swiftlet Collocalia francica on Mauritius, by protection of a nesting cave. (Unpublished report to the Fauna and Flora Preservation Society, UK, Dec. 1993)

Saddul, Prem 1995 Mauritius: a geomorphological analysis. Geography of Mauritius Series #3. Mahatma Gandhi Institute: Moka 340 pp.

[Saint-Pierre, Bernardin de] 1773. Voyage à l'Isle de France, à l'Isle de Bourbon, au Cap de Bonne Espérance par un officer du Roi. Amsterdam, vol. 1, Letter xvi, p. 249-254.