Diets of Cape clawless otters at two South African coastal localities

Abstract

The diet of the Cape clawless otter Aonyx capensis was investigated at the Dwessa Nature Re serve and Mkambati Nature Reserve on the Wild Coast, Eastern Cape Province, South Africa. Their diet was more varied at Mkambati (15 prey species) than Dwessa (7 species). In terms of percentage relative frequency of occurrence, the spiny lobster Panulirus homarus was found to be the most common prey item at both Mkambati (37.93%) and at Dwessa (35.21%), followed by fish (31.03% and 36.62%, respectively), crab (22.41% and 19.72%) and molluscs (3.11% and 4.23%). No significant differences were found in spraint dry masses between sites (15.10 g vs 17.95 g) or between masses of the diet categories for the two regions, bt, when converted to ‘fresh’ mass, mean spraint mass was significantly lower at Mkambati than Dwessa (108.08 g and 135.73 g, respectively). When diet categories were compared using ANOVA, only fish were found to be significantly different when expressed as fresh mass. Spiny lobster mandibles collected from spraints were used to estimate otter prey size preferences by comparing with wild caught lobster dimensions (ANCOVA, paired t tests, correlation and regression).  Otters ate spiny lobsters with carapace lengths between 39.5 and 72.0 mm CL. Differences in diet were compared with published data from elsewhere. Lobster and fish are relatively abundant within these reserves, suggesting prey availability rather than selective feeding influenced diet.

Key words: Aonyx capensis, spraint analysis, diet, predation, prey sizes.