Volume 19 Issue 1 Pages 1 - 61 (April 2002)

Citation: Jacques, H., Moutou, F. & Alary, F. (2002) On the Tracks of the Congo Clawless Otter (Aonyx congicus) in Gabon. IUCN Otter Spec. Group Bull. 19(1): 40 - 50

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On the Tracks of the Congo Clawless Otter (Aonyx congicus) in Gabon)

Hélène Jacques¹, François Moutou² and Franck Alary³

¹DVM, 13 Place de Verdun, 38320 EYBENS, France, e-mail: h.jacques.otter@wanadoo.fr
² DVM, 125 Avenue de Versailles, 75016 PARIS, France, e-mail: fmoutou@noos.fr 
³81 rue Raymond Poincaré, 33110 BORDEAUX, France, e-mail: umtami@yahoo.com

(received 3 May 2002, accepted 5 June 2002)

INTRODUCTION 

Four species of otters are known to exist in Africa. The distribution range of the Eurasian otter (Lutra lutra) is limited to Morocco, Algeria and Tunisia. The spotted-necked otter (Lutra maculicollis) occurs in the wetlands of sub-Saharan areas along with the Cape clawless otter (Aonyx capensis), except in the Congo River basin where the Congo clawless otter (Aonyx congicus) replaces it.

Due to the remoteness of the equatorial rainforests of central Africa, and other difficulties in working there, the distribution, status, and biology of the latter species are very poorly known.

The Otter Specialist Group would like to increase knowledge and conservation activities on African otters, as agreed at the OSG meetings in Hankensbüttel, Germany (November 2000) and in January 2001 at Valdivia, Chile (REUTHER, 2001). As the Regional Representative for the French speaking African countries, I have been initiating a survey on A. congicus, mainly in Gabon, and in Congo in the near future. In these countries, among the 2 species of Aonyx, only A. congicus occurs and no confusion is possible with A. capensis. Data concerning the distribution of L. maculicollis have also been gathered in Gabon.

METHODS

Bibliography and Visits to Museums
An extensive review of the bibliography and Internet addresses of collections has been conducted, whilst trying to sort out the main characteristics which define the 2 African Aonyx species.

Visits to the collections of the Central Africa Royal Museum (Tervuren, Belgium) and the National Museum of Natural History (Paris, France) were useful for establishing criteria for the differentiation, but some skins were found that appeared to be intermediate between the 2 Aonyx species.

SURVEY METHODOLOGY

Semi-structured interviews were carried out with local fishermen, forest utilisers, and gamewardens to obtain general information about the existence of otters and human impacts on otter populations.

Active observations, both of otters and their signs (tracks, spraints), were undertaken. Due to the similar shape of the hands and feet (around 11 cm long and 8 cm wide without prints of claws or webbing), prints of A. congicus were expected to be almost the same as those of A. capensis. The spraints have never been described before,
therefore, we also focused on those animals whose droppings could be confused with those of A. congicus.

In an attempt to form a network of key informants, a number of meetings with scientists from different institutions all over Central Africa were organised.

SURVEY SITES

Gabon lies on the equator on the west coast of Africa and covers an area of 267 000 km², 85% of which is covered by tropical rainforest. Four sites were selected, 2 of them being currently protected (Gamba complex, Lopé Reserve), one just about to be (Langoué baï), and one not yet protected (Mission, St Anne).

The African equatorial rainforest is a very harsh environment. Amongst the difficulties we experienced were a lack of roads, resulting in most of the movement inside the forest being undertaken by foot, wild animals, such as elephants and gorillas, almost invisible in the vegetation and easy to encounter unawares, and diseases (Ebola, Malaria, Yellow fewer, Hepatitis).

The climate is very much the same all over Gabon, with an average temperature around 25°, and 2 wet seasons; one from February to May and the other from September to December, with annual rainfall between 1500 and 3000 mm.

The Gamba Protected Area Complex, situated along the southwest coastal zone of Gabon, is composed of eight protected areas, including the Setté Cama, Iguela, Petit Loango, Ngove-Ndogo, Monts Doudoua, and Moukalaba reserves, totaling 11,320 km².

The Complex hosts a mosaic of ecological habitat types, including sandy seashores, freshwater lagoons, mangrove swamps, tropical forests (both selectively logged), gallery forests, secondary grasslands, and grassy savannas. The complex is important with respect to the Africa distribution of wildlife as it represents the extreme linkages between the tropical forests of Central Africa and the savannah ecosystems of southern Africa.

Due to the limited amount of time (7 days), we stayed most of the week in Setté Cama (02°30'S, 09°44'E), a little village situated on a narrow strip of sand between the sea and the lagoon. We surveyed the Nature trail 3 times, which goes along the lagoon from Setté Cama village to a point 4 km north of it. A day in Petit Loango (02°23'S, 09°37'E) allowed us to survey 10 km of forest. At both these sites, otter signs such as tracks and droppings were the focus.

La Lopé Reserve (0°03'-1°10'S, 11°17'-11°50'E) is situated in the centre of Gabon near the Ogooué River, the main river of Gabon, totalling 536 km² of mainly tropical rainforest. A research station on primates has been in operation here since 1963. We collected information about otters in the la Lopé Reserve and looked through documentation for 2 days. We also spent one day surveying the banks of the Ogooué River in front of la Lopé village.

Langoué baï (00°11'S, 12°33'E) is situated in central eastern region of Gabon. A baï is a kind of clearing in the forest, with a river and sometimes some salt marshs. Animals such as elephants (Loxodonta africana), gorillas (Gorilla gorilla) and sitatungas (Tragelaphus spekii) frequent these areas, probably to get salt. Otters are more easily seen in these open biotopes than in the forest. Langoué is the only baï in Gabon 'easily' accessible to scientists; 'easily', however, means a 38 km walk through dense jungle. We looked for otter signs on every river crossed on the way to the baï (3 days there, 2 days back) as well as on the baï itself (4 days there).

Mission St Anne is located not far from the sea, on the west coast near the town of Omboué. The Fernan Vaz lagoon is a complex of rivers mixing with the sea.

RESULTS

Brief bibliography synthesis
Aonyx congica is very often found in the literature, however, A. congicus is now considered the correct spelling. As the Greek onux is masculine and the species group name is a Latin adjective, it must agree in gender with the generic name (van ZYLL de JONG 1987; van BREE et al. 1999).

LÖNNBERG (1910) was the first to describe A. congicus from a specimen coming from the lower Congo, but called it A. capensis congica, thinking it was a subspecies of A. capensis with small molars. Pohle (1920) described a new species, A. microdon, from specimens coming from Cameroon and HINTON (1921) gave a very good description of 2 specimens coming from Uganda, placing A. congicus in a new genus, Paraonyx, which would include all African clawless otters with small molars. The subspecies therefore became Paraonyx philippsi from Uganda, Paraonyx congica from lower Congo and Paraonyx microdon from Cameroon. He added: "Nothing is yet known of the habits of these remarkable otters". Eighty-one years after this situation little has changed! ALLEN (1924) described 13 specimens of what he called A. capensis, though some of these could be A. congicus (SHOUTEDEN, 1942). A picture of an A. congicus cub is available on line at www.diglibl.arrmh.org (Chapin and Lang mission 1909-1915) and is clearly misquoted as A. capensis.

DAVIS (1978) thinks that the genus Paraonyx does not appear to be valid because tooth size varies geographically and Paraonyx could be a variant adapted to a different composition of prey species in the forested habitats of west central Africa. However, both van ZYLL de JONG (1972) and WOZENCRAFT (1993) recognised A. congicus and A. capensis as separate species. Within A. congicus, KINGDON (1997) recognised 3 sub-species, as did HINTON and HARRIS (1968), but recent authorities consider the species monotypic (WOZENCRAFT, 1993).

Criteria for differentiation between the 2 Aonyx species
Based on criteria given by different authors and on our personal observations of skins, photos, and sightings of individuals, we propose the following external criteria for identification (Table 1).

With A. congicus, the contrast between the upper and the ventral parts of the anterior part of the body is weakened by the silvery frosting of the head and shoulders (HINTON 1921). The frosting is due to the silvery tips of most of the longer hairs. Throughout the back to the root of the tail many of the longer hairs are similarly tipped
with silver, but such hair-tips are neither sufficiently numerous nor sufficiently long to produce more than a distinct and regular peppering pattern (HINTON, 1921).

The absence of the super-ciliary tufts in A congicus was not mentioned as a skin in the Paris museum clearly has some.

Cheek tooth size (P⁴, M¹ and M₁, M₂) is classically mentioned as representing a good criterium to distinguish A. capensis (large sized cheek teeth linked to an alimentation including crabs (ROWE-ROWE, 1977) from A. congicus (cheek teeth slender and weaker, linked to an alimentation of softer prey). A statistical analysis is about to be undertaken on museum skulls to find an index and to fix a threshold between the two species.

All the criteria given above are quite subjective, and can only really be used when both species are side by side for comparison. In a museum, such comparisons are easy to check but, in the field, distance of observation and wet fur may well prevent the use of these details.

Visits to collections
The collections of the Central Africa Royal Museum hold 32 skins of A. congicus, 17 skins of A. capensis, and 3 stuffed cubs of A. congicus. The 30 skulls of A. congicus were on loan when we visited the museum. We noticed that some skins were quoted as A. congicus on the tag and A. capensis in the catalogue.

The National Museum of Natural History, has 5 skins of A. congicus and 1 skin of A. capensis, and 3 skulls of A. congicus and 1 of A. capensis; 2 skins and 1 skull were, however, misquoted.

All these misidentifications confirm the fact that the two species are very close in appearance and some better identification criteria are needed.

As far as it is possible to say today, following the examination of 58 skins in museum collections and analysis of several photos and video footage by the authors, the best criteria for differentiation remains the quadrangular black patch located between the nose pad and the eye, circled by white in A. congicus and mixing with the brown fur of the same colour in A. capensis. Even so, some skins from the Democratic Republic of Congo (formerly Zaire) clearly show some intermediate forms, though most of these come from areas at the limits of the known distribution range of A. congicus.

MISSIONS TO GABON

Setté Cama in the Gamba Complex
Through interviews, it would appear that no otter has ever been seen in the area of Setté Cama (gamewardens, A. Greth, pers. comm.), although we got interesting data from rivers farther upstream of the sea (Ndogo River and Lake Kivoro). The main results in this area were the profusion of tracks and droppings of water mongoose (Atilax paludinosus), faeces of which could be easily confused with Aonyx.  STUART (1998) gives a size of about 20 mm in diameter for water mongoose droppings, up to 30 mm for Cape clawless otter, and 15 mm on average for droppings of spotted necked otter. Otters crush and eat the entire crab, whereas Atilax paludinosus usually leaves the carapace, pincers and legs of larger crabs (STUART, 1993). ROWE-ROWE (1977) gives a mean scat diameter for A. paludinosus of 18.8 mm (15-22), 25.1 mm (20-32) for A. capensis, and 14.5 mm (11-21) for L. maculicollis.

The faeces that we found all over the area, were sometimes single specimens, and sometimes gathered in latrines. They were mainly composed of crab remains and the diameter was from 18 to 30 mm with a mean diameter of 23 mm, larger than the usual diameter of water mongoose droppings. Nevertheless, in most of them it was possible to find the characteristic banded hair belonging to A. paludinosus. With a single spraint, confusion could be easy between Aonyx and A. paludinosus in this area where the diameter of the A. paludinosus spraints is bigger than previously recorded.

Lopé reserve
We were not fortunate enough to find any signs of otters but we gather information (Table 2). Both species of otters are present in the reserve as already quoted (Anonymous 1994).

Langoué Baï
Many tracks of A. congicus were found on the way to the baï and one individual was the baï (Table 3). Among the 5 rivers prospected, 4 of them were used by A. congicus, as indicated by the unmistakable tracks. Four of the rivers were very small, from 1 to 5 meters wide and 10 cm to 1 m deep, the fifth one was about 30 meters wide. None of the rivers were could be considered as 'marshy', although the banks were muddy in some places.

Mission to St Anne area
This lagoon is situated along the west coast of Gabon and contains otters according to reports of locals. Based upon the description given by fishermen, a picture taken by C. Wilks of a L. maculicollis drowned in a fishtrap, and a sighting by A. Falcone (pers.com.), we think L. maculicollis is more widespread in this area than A. congicus. However, due to their being hunted, along with other wildlife, otters are difficult to see in this area.

DATA ON DISTRIBUTION IN CENTRAL AFRICA

About 30 reliable records of A. congicus were collected from the following countries. Cameroon: Abong Mbang (W. Bergman, pers. comm.), Dja Reserve (F. Alary, pers. comm.), north of Dja Reserve (H. Planton, pers. comm.); Central African Republic: Dzanga-Sangha National Park (A. Turkalo, J. Ray, pers. comm.); Congo: the Nouabale-Ndoki and Odzala National Parks (B. Curran and E. Stokes, pers. comm. and J. M. Froment, pers. comm. respectively); and from Gabon: Lop&eacute reserve (L. White, pers. comm.), Langoué baï (cf this paper), the Liboumba, Louayé and Lodié rivers and surroundings (S. Lahm, in litt.), Makokou (P. de Watcher, pers. comm.), and Lekori (O. Bourry, pers. comm.).

Of interest, but not yet surveyed, is Nigeria as A. congicus is often quoted as occuring in this country. Present day Cameroon is, in fact, the result of the union of the former French Cameroon and part of Eastern Nigeria in 1968. Before 1968, the frontier, clearly shown on old atlases, was nearly straight along a line from Tchad lake to Douala. This has led to a number of misquotations! For example, HARRIS (1968) quotes Aonyx microdon occuring in Nigeria in the Ndop Plain, and ROSEVEAR (1974) puts this location in Cameroon, 40 km east of Bamenda. A further record in Nigeria was given by ROWE-ROWE (1995), but without any exact location. 

We contacted a team working in south-eastern Nigeria (ENIANG and LUISELLI, 2002) who gave us interesting data about A. capensis, but who doubt that there are any A. congicus in Nigeria (in litt.). A recent potentially reliable record for the old Mfameyi Forest needs to be confirmed by further studies as it could well be A. capensis (in litt). Neither Van ROMPAEY (1999) nor HAPPOLD (1987) mention A. congicus in Nigeria.

DISCUSSION

Although some authors thought that A. congicus may have vanished (e.g. REUTHER, 2001), this species does not seem to be particularly rare in Gabon as we collected reliable data in a short time.

Virgin rainforest appears to be the best place to collect signs of A. congicus. On the coast, due to the presence of more or less brackish water, disturbance, or lack of preferred food, no proof of this species was recorded. Further, an NGO (Aventures sans frontières, Protomac), working on sea turtles along the coast of Gabon for some time, has not seen or heard about otters. Further inland, in the freshwater lagoons and mangrove swamps located along the coast (Mission St Anne, Kivoro lake, Lambaréné lakes), records of A. congicus from locals are few. The presence of crabs does not seem to be an important factor for the presence of this species, as compared to A. capensis. This reinforces the statement that the smaller molars of A. congicus are associated with softer prey such as worms. The swamp otter, as A. congicus is also known, also seems to be at ease in both large and small rivers, according to many locals. So far, no records have been made in true swamps. In pristine rainforest, A. congicus seems to thrive, leaving many tracks and being relatively easy to see in clearings inside the forest.

Even in the museums visited, the skulls and skins of A. congicus outnumber A. capensis, though it is true that the Tervuren and Paris museums have been stocked from the French speaking part of Africa, i.e. mainly from the range of A. congicus. In comparison, the British Museum has 12 A. congicus skulls against 20 for A. capensis. Another interesting point is the existence of transitional forms between the 2 African Aonyx species. Some skins in the Tervueren Museum show intermediate patterns. In particular, there are examples of A. capensis showing a patch between the eye and nose more conspicuous than normal, these coming from areas situated at the limits of the distribution range of A. congicus. The possible existence of areas of sympatry between the 2 Aonyx species, with individuals morphologically intermediate, needs to be investigated. This kind of hybrid form has been described for savannah and forest elephants in the Garamba National Park (ROCA, 2001) and the same question has arisen for northern Angola (De BARROS, 1967). Sympatric areas are also suspected in Garamba (both Aonyx species have been found in the park and skins of both species are labelled from areas near the park in the Tervuren museum), and in Cameroon, which hosts both savannah and forest biomes.

THREATS IN GABON

Habitat destruction does not seem to be a threat for otters at the present time. Tropical evergreen lowland forest presently covers 85% of Gabon (Guineo-Congolian rainforest) and the annual rate of deforestation is around 0.5% (WCI, 2000), less than that of many other tropical countries. Nearly half of the forest has never been exploited. The population density is very low, with only 1 million people, and is concentrated mainly in towns; overfishing or human disturbance are, therefore, a problem in only a few areas. In a few rivers where A. congicus is considered as a competitor for fish, they are killed (S. Etouk, pers. comm.) or the place avoided (S. Lamh, pers.com.). We have a few records of otters drowned in fish traps but L. maculicollis seems to be more concerned than A. congicus. Sometimes, a cub is caught in order to try to sell it to Europeans. We know of 2 cases of this, in August 1968 (P. Charles Dominique, pers.comm.) and in January 2002 (O. Bourry, pers.com.); In both cases, the cub did not survive. Hairs were taken from the second animal for genetic sampling, and pictures were taken of both.

The main threat for otters, and many other species, remains hunting for bush meat. The two species of otters are not legally protected in Gabon except in reserves. Nevertheless, otters are not particularly appreciated as bush meat because of the bad ('fishy') taste of the meat and the difficulties in catching the animal. They are caught in snares or shot whilst being chased by dogs. An otter is sold for between 10 to 15 US$. The guts or the penis are considered as an aphrodisiac but no more so than other animals such as crocodiles. In Southern Cameroon, the problem is more acute (cf F. Alary report), and we have gathered 4 different reports describing otters sold as bush meat in the Dja and Abang Mbang areas, all with photos showing clearly A. congicus.

FUTURE PROSPECTS

In July 2002, we plan to stay 3 weeks in the Nouabale Ndoki National Park in Northern Congo, where A. congicus is very often seen in one of the baïs by scientists working on gorillas and elephants. The aim of this mission will be to study the species biology.

The collections of skulls of both species of African Aonyx, in the Tervuren and British museums, will be measured and a statistical study will be conducted. The skins from these two museums will be re-examined to produce more reliable criteria for identification.

Threats will be evaluated in the Congo and, more specifically, in Cameroon.

The network of informants will be extended in order to get further data on the 3 species of otters in west and central Africa.

CONCLUSION

This study has provided evidence for the presence of A. congicus in Gabon, provided more precise data on the distribution in central Africa, as well as raised new questions about possible areas of sympatry between the 2 African Aonyx species.

ACKNOWLEDGEMENTS - We wish to thank the IUCN/SCC - Otter Specialist Group, the van Tienhoven Foundation for its financial and constant support, the Fauna and Hunting Direction in Gabon for field work authorisation, the Wildlife Conservation Society, WWF Gabon and the International Centre for Medical Research (CIRMF) of Franceville for their welcome and help in organising the mission. Further, we would like to thank the Tervuren Royal Museum and Paris Muséum National d'Histoire Naturelle for access to their collections, the French Mammal Society (SFEPM) for documentary and editing support, and Dr. Olivier Bourry for pictures of A. congicus.

REFERENCES

Résumé : Sur les Traces de la Loutre du Congo (Aonyx congicus) au Gabon
La répartition et le statut de la loutre du Congo (Aonyx congicus Lönnberg, 1910,lutrinae, mustelidae, camivora) doivent être étudies dans les forêts tropicales d'Afrique Centrale où l'espèce est réputée présente. Aucune recherche n'y a été conduite jusqu'à présent, vraisemblablement du fait de 1'éloignement de ces zones.
Une première mission de 15 jours au Gabon (Juillet 2001: St Anne) suivie d'une autre de 4 semaines (Janvier 2002: Setté Cama, Lopée reserve, Langoué baï) nous a permis de collector des informations sur A. congicus, d'observer 1'animal ou ses traces, et d'initier la mise en place d'un réseau d'information non seulement au Gabon mais aussi en Afrique Centrale. A. congicus semble prospère dans les forêts tropicales intérieures, la principale menace étant la chasse pour la viande, principalement au sud du Cameroun mais aussi apparemment, à une échelle plus réduite, au Gabon.
Revenez au dessus

Resumen: Tras las Huellas de la Nutria del Congo (Aonyx congicus) en Gabón
Aún no ha sido evaluada la distribución y el estado de la nutria del Congo (Aonyx congicus Lönnberg, 1910, lutrinae, mustelidae, camivora) en las selvas de África Central, donde se dice que la especie ocurre. Probablemente debido a lo remoto de tales áreas, no se han conducido estudios hasta la fecha.
Una misión a Gabón de 15 días (Julio de 2001: St Anne), seguida de una de 4 semanas (Enero de 2002: Setté Cama, reserva Lopé, Langoué baï) nos permitió recoger información sobre A congicus, ver el animal y varias huellas, y comenzar a establecer una red para recabar información no sólo en Gabón, sino en África Central. A. congicus parece prosperar en selvas tropicales virgenes del interior. Su mayor amenaza es la caza por su carne, en particular en el sur de Camerún, pero aparentemente también en una menor escala en Gabón.
Vuelva a la tapa

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