This site consists of a string of permanent freshwater lakes and additional temporarily wet depressions (niayes) lying along a line running north-east from the outskirts of Dakar to around 60 km south-west of St Louis. The lakes lie behind the ridge of coastal sandy dunes, in shallow depressions at 1–4 m above sea-level, over a distance of c.150 km. They are replenished both by rainfall and from the underlying water-table, which lies close to the surface. The wetlands cover 40 km² at low water; at high water, all the lakes can increase their surface area five-fold. The largest lakes lie at the southern end and include Nhiarhol Pool and the lakes Mbao, Mbeubeussé, Retba, Tanma, Youyi (or Malika) and Ourouaye. Lake Retba is the largest, with an open water surface of 5 km by 1.7 km wide at low water. Niaye Hann Mariste consists of a depression covering a surface area of about 30 ha (1.3 km by 200 m), but this dried out completely in 1997 due to evaporation, compounded by abstraction of water for agriculture and building construction. The surrounding vegetation is subjected to seasonal inundation and the area is characterized by the oil-palm Elaeis guineensis. There are also elements of vegetation more typical of the Sudan–Guinea Savanna biome and Guinea–Congo Forests biome (e.g. Prosopis africana and Ficus capensis). These are able to flourish here due to the high moisture content of the soils, which results from the water-table lying close to the surface and the moisture-bearing Alizé winds blowing in from the Atlantic. The whole site is very important in terms of human use, for cattle-grazing, fishing, vegetable, fruit and rice-growing and market gardening (estimated at 90% of national production). Many of the individual lakes also have religious and cultural significance.
See Box for key species. The lakes were included for the first time in the African Waterbird Census in 1997, when nearly 4,000 birds were counted. The niayes have also been the subject of a number of recent more detailed studies (notably by Pierre Reynaud and colleagues at the Institut de recherche pour le développement, IRD), which reveal them to be some of the most ornithologically diverse and most threatened sites along the whole coast of Senegal. In Niaye Hann Mariste alone, Reynaud has recorded 147 bird species, including 51 breeding. The niayes as a whole are particularly important for a wide variety of breeding and wintering waterbirds and also raptors. Up to 500 Phoenicopterus minor were recorded at Lac Tanma in 1990, Falco naumanni is reported in small numbers from the site and there are huge roosts of Milvus migrans.Phoenicopterus ruber is a regular winter visitor and the site appears to play a key staging role for birds coming from regions further north (Baillon pers. comm.). A maximum count of 3,000 was recorded in 1975 on Lac Tanma; if these numbers are a regular occurrence, they will additionally qualify the site as an IBA. Similarly, a maximum number of 3,200 Recurvirostraavosetta recorded on Lac Youyi in 1975 would qualify this lake as an IBA in its own right, if regularly occurring; the species is also regularly recorded elsewhere within the site. In addition to those in the Box, other species wintering in significant numbers include Egretta garzetta and Anas clypeata. There are records of large numbers of wintering and passage Sterna sandvicensis (7,500 between site SN006, Parc National de la Langue de Barbarie, and the town of Kayar; plus 13,000 from Kayar to Cap Vert) and S. albifrons (1,500 between Kayar and Cap Vert). In both these cases, the numbers will include birds using the niayes, but these counts also cover a wider area including the whole coastal strip. Breeding birds recorded on the site include Phalacrocorax africanus. Six species of the Sudan–Guinea Savanna (A04) biome have been recorded from this site (see Table 2), reflecting the humid coastal climate, which encourages vegetation-types typical of more southerly zones.
Non-bird biodiversity: None known to BirdLife International.
Pressure/threats to key biodiversity
The niayes have no protected status under national conservation legislation and there is no active conservation management (despite representations made to the authorities about the ecological and educational values and threats to the site). The whole site is threatened by human encroachment and various forms of development, particularly those niayes such as Hann Mariste and Pikine-Guédiawaye that are within or close to Dakar and to the main road leading east and north out of the capital. One of the main threats is from drainage and land reclamation for building, which is proceeding very fast. Over-abstraction of water and various forms of pollution threaten the hydrology and water quality of the underlying water-table. In addition to their immediate conservation value, the niayes represent a huge educational resource (large numbers of easily visible, interesting birds, very close to dense urban centres), which will also be lost if the site is further degraded. This situation is extremely urgent, with one niaye (Thiaroye) almost completely destroyed and bulldozers removing the trees and hedges which stabilized the dunes around Niaye Hann Mariste in late 1998. For the purposes of this publication, the whole group of lakes and depressions has been grouped together as one IBA because the data are not sufficient to distinguish smaller individual IBA sites. Further work should help to identify those sites of particular importance and which should be nominated for protected-area status and/or conservation action.
BirdLife International (2023) Important Bird Areas factsheet: Niayes (from Dakar to St Louis). Downloaded from
http://www.birdlife.org on 07/02/2023.