Variability in milk fatty acids: recreating a foraging trip to test dietary predictions in Antarctic fur seals

Using Antarctic fur seals (Arctocephalus gazella (Peters, 1875)) in a feeding trial, we investigated the use of milk fatty acids to determine diet. In a regime designed to replicate an average foraging trip, six female seals were fed on four successive days meals of krill (Euphausia superba Dana, 1850; day 1), mixed krill and icefish (Champsocephalus gunnari Lönnberg, 1905; day 2), and icefish (days 3 and 4). Four milk samples were collected from each female, one every 12 h from the time of the last feed. Fatty acid profiles of samples were analysed using canonical discriminant analysis and classification trees. Milk fatty acids could be used to distinguish between seals fed the experimental diet, which was high in fish, and those feeding naturally, thought to be consuming mostly krill. However, there was significant variation between individual seals, which may have been the influence of feeding prior to the experiment. Milk fatty acids remained relatively unchanged over time, suggesting that the influence of dietary fatty acids was averaged over the suckling period. We conclude that, whilst this technique has potential in studying the diet of higher predators, further work is needed to test the underlying assumptions and mechanisms involved in the transfer of fatty acids from the diet into milk.

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