Volume 7 Pages 1 - 43 (February 1992)

Citation: Nel, J.A.J. (1992) Current Research on the Cape Clawless Otter in the Southwestern Cape Province, South Africa IUCN Otter Spec. Group Bull. 7: 36 - 37

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Current Research on the Cape Clawless Otter in the Southwestern Cape Province, South Africa

Jan A.J. Nel

Dept of Zoology, University of Stellenbosch, Stellenbosch, 7600 South Africa

During 1990 a pilot study was conducted to document the occurrence of Aonyx capensis in the Breede River, and to relate its presence in specific stretches of the river to physical aspects of the river itself, as well as land-use practices in the surrounding countryside. It became clear that A. capensis might be more widespread than previously thought, and that useful information can be obtained through walking the riverbanks, using canoes in inaccessible parts, and questioning farmers and other riparian users. Spraints were also collected seasonally along a 2 km stretch of riverbank along a tributary of the Breede River, viz the Knigna river, near the village of Montagu. Crabs (Potamonaules sp.) predominated in the diet of the clawless otters in this area throughout the year, although other prey items showed an increase in incidence in scats during winter.

During 1991 a more intensive study was launched on the diet, and possible prey selection, of A. capensis occurring below the Bulshoek Dam in the Olifants River, some 20 km N. of Clanwilliam. During a visit by Dr Hans Kruuk, Institute of Terrestrial Ecology, Banchory Research Station, Scotland, who will collaborate in the project, analyses of spraints from various other rivers, as well as from the study site, indicated that crabs - again Potamonautes sp. -predominate in the diet. As the eye-stalks of the crab eaten are often intact in spraints, a collection of crabs allowed correlation of eye-stalk length with carapace width and crab weight; consequently size-classes of crabs eaten can be ascertained. Spraints were collected on a seasonal basis and analyzed, and again crabs were found to predominate (percentage occurrence) throughout the year although fish were taken to a noticeable extent during winter. Sampling of crabs in the river was not thorough enough, however, to say if the otters selected for specific size classes of crabs, or whether size of prey taken merely reflects the relative availability of the size class.

Sprainting areas were noted and further studies will analyse prey selection in greater depth. All sightings of otters are noted to gain data on activity cycles, and in clue course individuals will be fitted with radios as the study area is very suitable for radio-tracking. Surveys of otter occurrence in other rivers is also in progress, to gain a better idea of otter distribution and abundance in this part of Africa.

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