The presence, diet and relative abundance of otters (Carnivora: Mustelidae) in Northern Namibia
Four species of otters (Carnivora: Mustelidae) are known to occur in Africa: Eurasian otter Lutra lutra, spotted-necked otter Hydrictis maculicollis, African clawless otter Aonyx capensis and the Congo clawless otter Aonyx congicus. The African clawless and Spotted-necked otters are known to occur in Namibia although very little is known about their biology and distribution. IUCN Red List of Threatened Species indicated the status of African clawless and spotted-necked otters to be near threatened due to a reported decline in their numbers primarily due to habitat loss and destruction, mainly from unsustainable agricultural land expansion, human and otter conflict, invasive species, river pollution as well as widespread continent-wide decrease in river water quality. The collection and use of faecal samples and camera trapping have become an important non-invasive source of information, especially when dealing with elusive animals. The specific objectives of this study were to determine the presence of otter species that occur in the Kunene and Okavango rivers, their diet as well as their relative abundance. Community sightings of otters were utilized, along with on sight observations (for example, sightings and signs) while collecting data in the field to determine the presence of otter species. Sightings of the African clawless and Spotted-necked otters, as well as signs (footprints) of the two species of otters were recorded as an indication that both species do occur in Namibia. In order to determine the diet of otters, spraints were collected along the banks of the two rivers, air dried, teased apart and prey remains identified by utilizing a stereomicroscope. Prey remnants were sorted into major categories and recorded. Prey items such as crabs, frogs, fish, plant material and insects were found in the otter spraints. Due to the small sample size of spraints collected, it could be possible that not all potential prey items were available for recording. A total of 40 cameras were deployed along the banks of the Okavango River within the Bwabwata National Park, recording a total of 967 camera days. Due to extremely low detection of the Spotted iii and African clawless otters (3 encounters), no density estimates were computed. Instead, a relative abundance index (RAI) of 0.3 of African clawless otter was calculated and compared to RAIs data obtained from six natural areas around Southern Africa. Results suggest that the Relative abundance index (RAI) of 0.3 for the Okavango River was the lowest compared to similar studies done elsewhere in southern Africa. A species accumulation curve for all mammals photo-captured in the study area was plotted which nearly reached an asymptote (with 21 captured species), suggesting that the inventory on species composition in this phase was more complete. Conservation of the wetlands and restoration of water quality might be the most important steps towards ensuring the future of otters in Namibia. There is also a need for a more expansive study to be conducted on the taxonomy, distribution, diet, and population density of otters that occur in all northern perennial rivers of Namibia.
African clawless otter, Camera Traps, Diet, Elusive animals, Faecal samples, Population Density, Relative abundance index (RAI), Spotted-necked otter, Species accumulation curve, Namibia, University of Namibia
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