River conservation in Madagascar
J.P. Benstead, M.L.J. Stiassny, P.V. Loiselle, K.J. Riseng and N. Raminosoa
Madagascar’s extraordinary biological heritage makes the island one of the highest priorities for international conservation efforts. This ‘microcontinent’ is one of the 12 ‘megadiversity countries’ which together harbour 70% of the world’s plant and animal species (McNeeley et al., 1990). Its long isolation has resulted in the adaptive radiation of many groups and a correspondingly high level of endemism. Approximately 90% of the island’s species are found nowhere else (Battistini and Richard–Vindard, 1972; Jolly et al., 1984; International Union for Conservation of Nature and Natural Resources/United Nations Environment Programme/World Wildlife Fund – IUCN/UNEP/WWF, 1987; Nicoll and Langrand, 1989). Many of these taxa either belong to relic lineages that exist elsewhere only in the fossil record (Wright, 1997) or are basal representatives of their respective clades (Stiassny and DePinna, 1994; Stiassny and Raminosoa, 1994). Despite its biological riches, however, Madagascar is the 10th poorest nation in the world (Economist Intelligence Unit – EIU, 1994). Poverty, combined with a 3% population growth rate, has forced the country and its inhabitants into a familiar spiral of environmental degradation that is characterized by extensive deforestation and severe soil erosion (Jolly and Jolly, 1984; EIU, 1994). These processes are destroying Madagascar’s unique environments and driving many species to extinction.
Despite their high degree of vulnerability, the island’s biota and habitats remain poorly known. This is particularly true of the island’s river and stream ecosystems. As a result, the island’s endemic and highly threatened riverine biota are not being included in current conservation efforts. In addition, decisions relating to ecosystem protection and the design of nature reserves historically have not been made from a watershed perspective. Consequently, there is an urgent need for consideration of freshwater ecosystems and biota to be integrated into future conservation planning (Reinthal and Stiassny, 1991; Stiassny and Raminosoa, 1994).
Efforts to conserve Madagascar’s river ecosystems face immediate and daunting challenges. First, many of the island’s rivers have been severely affected by deforestation, subsequent erosion and sedimentation, the spread of exotic fish species, and overfishing. Restoration or rehabilitation of these damaged systems would be a monumental task. Second, those rivers on the island that are still relatively undisturbed are threatened with similar fates. The factors that are driving these changes include human population growth, a dwindling resource base, and a struggling economy (Jolly and Jolly, 1984). Third, information is a prerequisite to successful conservation. As outlined above, very little is known about Madagascar’s river ecosystems.
The main goal of this chapter is to draw together the sparse and disparate literature pertaining to river conservation in Madagascar. We concentrate on the data and information sources that are available and identify major gaps in an attempt to encourage more interest and research in the region. For example, our discussion of the river biota and its conservation status is biased towards the endemic fish fauna; other taxa are