Trophic overlap between three syntopic semi-aquatic carnivores: Cape clawless otter, spotted-necked otter and water mongoose
Drought conditions in the Eastern Cape Province, South Africa, from 1990 to 1993 caused much of the Bushmans River to dry up, thus forcing Cape clawless otters Aonyx capensis (Schinz), spotted-necked otters Lutra maculicollis (Lichtenstein) and water mongooses Atilax paludinosus (Cuvier) to coexist in restricted ranges. The diet of the three carnivores was compared by analysing their scats to determine the amount of trophic overlap. Expressed as relative percentage frequency, the three most common prey categories found in Cape clawless otter scats were crab Potamonautes perlatus (Milne Edwards) (51%), insect (19%) and fish Tilapia sparrmanii (Smith) (18%). In spotted-necked otter scats, fish (47%), crab (38%) and frog (8%) were the most common, while in water mongoose scats, insect (28%), crab (26%) and mammal (15%) were most abundant. Water mongooses and spotted-necked otters ate similar sizes of crabs, significantly larger than those eaten by the Cape clawless otters. Cape clawless otters ate a wide range of crab sizes, including specimens much larger than those taken by the other two carnivores. Cape clawless otters and water mongooses ate similar size fish, significantly smaller than spotted-necked otters. The results show that even during enforced cohabitation in a relatively small range during drought conditions, there is separation of diets in these three carnivores.