The diet of female Australian fur seals as determined by animal-borne video cameras

Knowledge of predator diets is crucial for understanding their role in ecosystems. Due to their aquatic foraging habitat, the diets of pinnipeds has traditionally been investigated using faecal analysis, the limitations and biases of which have been well documented. In this study, the prey of adult female Australian fur seals in northern Bass Strait, south-eastern Australia, was investigated with the use of animal-borne cameras. Video records (total 67 h) were obtained from 18 individuals during the winters of 2008-12, covering 1263 foraging dives. A total of 1693 prey encounter events were recorded, 1128 of which were sufficiently visible to be categorised (57.2 ± 14 per individual). A total of 26 prey types were identified. The main items consumed were red cod (FO = 78%, NA = 6.3 ± 2.6), gurnard spp. (FO = 72%, NA = 20.6 ± 5.2), leatherjacket spp. (FO = 72%, NA = 4.3 ± 1.2), Jack mackeral (FO = 50%, NA = 1.0 ± 0.3), octopus (FO = 56%, NA = 1.3 ± 0.4), redbait (FO = 50%, NA = 0.9 ± 0.3), and stingray spp. (FO = 28%, NA = 0.6 ± 0.4). The size of these prey were similar to previously reported but they were all observed in greater frequency and/or higher abundance than in previous faecal studies. While these differences could result from temporal variation in availability between this and previous studies, they may also reflect incomplete consumption of some prey leading to biases (e.g. the head of gurnards and the buccal mass in octopus were regularly observed to be discarded). The results also clearly indicated evidence for individual specialisations in diet and highlight the value of direct observations of prey consumption for determining diet composition in marine mammals.