The Cross-Sanaga Gorillas: the Northernmost Gorilla Populations

The gorillas north of the Sanaga River in Cameroon inhabit a fascinating region. The Cross-Sanaga landscape is one of the most biologically diverse expanses in Africa, with many areas showing evidence of having been forest refuges during the last ice age. At the same time, fertile soils throughout much of the region have encouraged human population growth and resettlement, so that it is also one of the most the most highly populated areas in West-Central Africa.
Gorilla populations throughout the northern section of this region are extremely patchy, scattered into several subpopulations and restricted, in most cases, to the remaining areas of higher altitude forest where human pressures are less. It is likely that this habitat fragmentation is a relatively recent phenomenon, although some particularly fertile areas of the northwestern area of Cameroon have been farmed intensely for several hundred years. It is certainly true that habitat fragmentation and degradation are still increasing, although the advent of several conservation initiatives in the past decade is now bearing fruit and there is now a more positive outlook for some areas.
There are three main gorilla populations north of the Sanaga river - the highly fragmented subpopulations of Cross River gorillas straddling the Cameroon-Nigerian border; the Ebo gorillas, probably a single population of gorillas less than 100 km north of the Sanaga river; and the Deng-Deng gorillas, in the area between the Lom-Pangar river system and the river Yong, west of Belabo.

The Cross River Gorilla Population in Cameroon and Nigeria
The Cross River gorilla Gorilla gorilla diehli is classified as critically endangered, with a total population of less than 300 individuals, split into at least 10 subpopulations. Primarily located in highland forest, Cross River gorillas throughout their range are scattered across a broad landscape which totals approximately 3000 km². Despite the fragmentation of this population, there still exist large tracts of forest linking subpopulations which, if they can be maintained, will continue to provide access routes to connect groups as well as accommodating any future range expansion which could support a growth in population.
The main threats to the future survival of Cross River gorillas are hunting, habitat loss and fragmentation. Through community education outreach activities and increased law enforcement measures, hunting over the past 7 years has become almost a secondary threat. Gorilla hunting has not been totally eradicated and a recent report from Cameroon suggests that one animal was killed in the last 6 months. This appears to be an isolated case and the first report received since 2003 in Cameroon, but with such a small population even the killing of one individual is still a major cause for concern.
Mount Cameroon is the highest peak in West-Central Africa and is part of an extensive chain of volcanic activity from Bioko, the offshore island of Equatorial Guinea, northwards to the Bamenda Highlands. The northern section of this mountainous region provides habitat to the largest proportion of Cross River gorillas.
Cameroon has approximately seven of the Cross River gorilla subpopulations, one of which is a true transboundary population, spending time in both Cameroon and Nigeria. The largest of these is believed to be around 25 weaned individuals and the smallest subpopulation may total as few as 10-15. The most current estimate of the total population within Cameroon is around 180-200. Presently, no Cross River gorilla subpopulation in Cameroon is located within a protected area although there are plans underway to rectify this.
Recently, a further sub-population of gorillas was located in the Bechati-Fossimondi-Besali forest, a non-classified forest area bordered by a long-term logging concession. This gorilla sub-population is likely to be small. Current research is being conducted by a Cameroon-based NGO, the Environment and Rural Development Foundation (ERuDeF), with funding from Fauna and Flora International (FFI) and the Taiwan government.
The other three forest blocks inhabited by Cross River gorillas are in Nigeria. Two of these are located inside protected areas: the Cross River National Park, which was established in 1991, and the Afi Mountain Wildlife Sanctuary, established in 2000. The other, geographically intermediate, population is located within the Mbe Mountains where negotiations are underway to establish a community-owned protected area. Preparation of a management strategy for the Cross River National Park is being undertaken by the Wildlife Conservation Society (WCS), working in conjunction with park management, and efforts over the past few years have been on monitoring, law enforcement and direct protection.
In both Cameroon and Nigeria, studies of gorilla ecology have been conducted. Gorilla monitoring is currently undertaken on both sides of the international border. In Nigeria all three subpopulations and the transboundary population are monitored on a regular basis and in Cameroon there are imminent plans for a recensus of all subpopulations (the last estimate of the entire Cameroon population was conducted in 2001).

The Gorillas of the Ebo Forest
The Ebo forest is situated just north of the Sanaga River and covers almost 1,500 km² of rugged, boulder-covered mountains and steep valleys, with undisturbed closed canopy forest on the mountain tops and disturbed old secondary vegetation at the valley floors (more details). The Ebo Forest Research Station was established in the heart of the forest in April 2005, with the aim of studying the small gorilla population as well as the ten other diurnal primate species existing at the site.
Evidence has been found of gorillas in the central region of the forest where there is at least one group of up to 12 weaned gorillas, and a solitary male gorilla. Recently, ground nests have also been recorded to the west of the Ebo river, 22 km west of observations in 2002 (Morgan et al. 2003). It seems likely that this subpopulation of gorillas is very small.
These gorillas are under threat from hunting pressure, which is particularly high in this region due to its proximity to large cities such as Douala and Yaoundé. On February 3rd 2006, gorilla meat originating from the Ebo forest was sold in Douala. This is the first known poaching of a gorilla since the establishment of the research station. At the time of writing, no one has been apprehended for this crime.

The Gorillas of the Belabo Region
Approximately 320 km northeast of the Ebo forest are the forests of the Belabo region. Here, a population of gorillas was surveyed by Eno Nku and Sunderland-Groves in 2001/2002 (Fotso et al. 2002), and appears to be restricted to three forest blocks in the region - the Deng-Deng Forest Reserve, the area around the Sanaga-Yong chimpanzee sanctuary and a small patch of forest situated to the northeast of Nanga Eboko.
Transect surveys in the three forest blocks indicated significant gorilla densities, particularly in the Deng-Deng Forest Reserve, and good numbers of chimpanzees. However, as in other regions, the main threat is hunting for the commercial bushmeat trade.

Taxonomy
Sarmiento and Oates (2000) confirmed the Cross River gorillas as a distinct sub-species based on a comprehensive analysis of cranial material in museum collections. An additional 34 Cross River gorilla crania (10% of the total surviving population) have been collected by Sunderland-Groves and co-workers over the past decade, and it is hoped that these additional crania, all of which were collected without payment, can be used for future morphological studies.
The one cranium in existence from the Ebo region suggests more morphological similarities with western lowland gorilla populations south of the Sanaga River than with the Cross River gorillas. Interestingly, a recent article in Gorilla Journal has raised the possibility that the Ebo gorillas may be a relict population of a formerly more widespread population living north of the Sanaga River, based on Discriminant Analysis of the Ebo cranium comparing it to Cross River, Cameroon coast and Cameroon plateau gorilla crania.
Genetic work is currently being conducted on many of these gorilla populations. Microsatellite DNA analysis from faecal samples of the majority of Cross River gorilla subpopulations is being undertaken by Rich Bergl of Central University of New York in collaboration with the Max Planck Institute for Evolutionary Anthropology in Leipzig. Faecal samples from the Ebo forest gorillas are being analysed by Oliver Ryder and colleagues at Conservation and Research for Endangered Species (CRES), at the Zoological Society of San Diego, and hair samples are being analysed by Nicola Anthony of the University of New Orleans.

Conservation Outlook
With ever increasing human development activities, conservation in this region is challenging, but solutions must be sought.
Over the last year, two areas inhabited by Cross River gorillas in Cameroon have been proposed for new or increased protection status - the Takamanda Forest Reserve (currently a production forest) has been proposed as a National Park and the Kagwene Mountains as a Gorilla Sanctuary. Once created, three of the seven Cameroon Cross River gorilla subpopulations will be located within these protected sites. Proposals to protect the remaining subpopulations located on the periphery of Takamanda, the Mone Forest Reserve and the Mbulu forest, are under review within a larger landscape approach through the creation of a Technical Operations Unit. This initiative has been developed through a consortium of partners consisting of the Government of Cameroon, WCS, GTZ, the German Development Bank KfW and others. This landscape plan will allow for both protection and sustainable use of forests, ensuring the unique biodiversity is maintained.
In Nigeria two of the three forest blocks where Cross River gorillas occur are already officially protected and, as mentioned above, there are plans underway to create a community-led conservation effort for the remaining area, Mbe.
Although research and monitoring continue in both countries, emphasis over the past few years has shifted to direct conservation action. The WCS Cross River gorilla conservation program supports range state governments working with local communities to increase the survival prospects of Cross River gorillas and other endangered species through supporting law enforcement efforts, community education outreach programs and management planning.
The establishment of a permanent research station in the Ebo forest in early 2005 has already yielded some protection against hunting in the centre of the forest, although there is increasing pressure from hunters to recommence their activities in the research area. The Ebo forest is due to be gazetted as a national park by the Government of Cameroon in 2006, with technical assistance from WWF Cameroon Coastal Forests Programme, which aims to achieve active protection of the area, which is currently under severe hunting pressure, especially at its periphery.
Plans are currently being reviewed for the status and management of the areas encompassing the Belabo gorilla population by the Government of Cameroon.
In summary, the northernmost gorillas in existence are split into numerous small, isolated subpopulations. The threats from hunters, together with the increasing pressures posed by habitat fragmentation and degradation, lead to an uncertain future for these gorillas. We hope that efforts by range state governments and the conservation community in the Cross-Sanaga region, supported by the international community, will gather strength, and that these important gorilla populations will have a secure future.

Bethan J. Morgan and Jacqueline L. Sunderland-Groves

The Cross River Gorilla Project in Cameroon is funded by the Wildlife Conservation Society, United States Fish and Wildlife Service through the Great Ape Conservation Fund, WWF African Great Apes Programme, the Margot Marsh Biodiversity Foundation and Columbus Zoo.
The Ebo Forest Research Project is funded by Conservation and Research for Endangered Species (CRES) of the Zoological Society of San Diego, the United States Fish and Wildlife Service through the Great Ape Conservation Fund, the Margot Marsh Biodiversity Foundation and the Offield Family Foundation.

References
Fotso, R. et al. (2002) Distribution and conservation status of gorilla population in the forests around Belabo, Eastern province, Cameroon. Unpublished report, Cameroon Oil Transportation Company (COTCO)
Morgan, B. J. et al. 2003. Newly discovered gorilla population in the Ebo forest. Littoral Province, Cameroon. International Journal of Primatology 24 (5), 1129-1137
Sarmiento, E. E. & Oates, J. F. (2000) The Cross river gorillas: A distinct subspecies, Gorilla gorilla diehli Matschie 1904. Am. Mus. Novitates 330, 1-55

Jacqueline L. Sunderland-Groves began working with primates in 1991 with Pandrillus in Nigeria. In 1997 she started a gorilla survey in the Takamanda Forest Reserve, and after 2000 she studied Cross River gorillas in other areas. She recently moved to Indonesia.
Dr. Bethan Morgan studied the ecology of forest elephants in the coastal forest of Gabon between 1997 and 1999. Since 2002 she has been working for the Zoological Society of San Diego's Center for the Reproduction of Endangered Species (CRES) in Cameroon, where she studies the ecology of large mammals, particularly drills.

Western gorilla overview

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