As of 1996, Limnogale mergulus is IUCN listed as endangered, based on the low number of known sites for the species and continued decline in its habitat. Many apparently suitable sites in eastern Madagascar do not support populations. Even more worrying is that Limnogale can no longer be found, or appears rare, at sites that were once known to support populations (e.g., Andekaleka and Antsampandrano). Declines appear to be linked to habitat alteration caused by deforestation and drowning in eel and crayfish traps (an additional and unquantified source of mortality). All the available evidence suggests therefore that Limnogale is rare and is being affected by habitat degradation.

Fecal pellet surveys at Ranomafana have indicated that Limnogale populations persist in streams not covered by a tree canopy (Benstead et al. 2001; see figure), and that this species is clearly not an obligate forest dweller. However, it feeds on a prey community that is extremely vulnerable to the erosion and subsequent sedimentation that is a common response to catchment deforestation. Such sedimentation has not occurred in the peripheral zone streams surveyed at Ranomafana (Benstead et al., in press). Prevention of sedimentation and maintenance of healthy prey communities is therefore of paramount importance in future efforts to conserve Limnogale, a classic indicator species of healthy benthic communities.

The greatest impediment to Limnogale's conservation, however, is the paucity of distributional data. While the 11 sites known to have supported populations in the past almost certainly represent an underestimate, the extent of the species' range remains largely unknown. This is almost entirely due to the fact that no wide-ranging survey of its distribution has been undertaken. Despite the recent expeditions and faunal inventories throughout Madagascar aimed at surveying small mammal populations, none have resulted in new locality records for Limnogale. Limnogale has never been collected using the methods currently and traditionally employed to survey small mammals; capturing specimens requires an inordinate amount of time and effort using techniques specific for semiaquatic mammals. Thus, while our knowledge of most Malagasy mammals grows at an ever-increasing rate, the status of Madagascar's most endangered small mammal remains as uncertain as it was when conservationists first called attention to its plight over a decade ago (Nicoll and Rathbun, 1990). These authors, in an IUCN Action Plan, proclaimed it "essential that the remaining aquatic tenrec localities are identified..." (p. 44). In the intervening dozen years, over 1.2 million hectares of Madagascar's eastern rainforests have been destroyed (Dufils, in press), affecting an estimated 48,000 km of streams and rivers (Benstead, unpubl. data).

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