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A glimpse into Pandora's box; DNA based analysis offers insight into the diet of the endangered Australian sea lion


Understanding the trophic interactions of high order marine predators presents many challengers trypically where diet must be inferred from semi-digested remains of prey retrieved from a predator's stomach, regurgitate or faecal material.  Fish sagittal otoliths and cephalopod beaks are the most common diagnostic structures to survive the disgestive process and universally used to identify prey to genus or species.  However, this method of identifying what a predator has consumed is confounded by inter or intra-species specific digestive variability, often resulting in unreliable estimates of the relative importance of the prey species consumed.  As a marine mammal, the Australian sea lion (Neophoca cinerea) typifies these digestive constraints, as it exhibits extreme digestive capabilities frequently resulting in poor prey identification restricting analysis to the most robust species. 

DNA-based molecular diagnostics are gaining popularity in dietary studies, as DNA can provide fine scale taxonomic resolution of the prey species consumed by a predator.  For the benthic foraging Australian sea lion, species level identification of prey taxa is imperative to the future management of the species, as it can provide integral trophic links to habitat use.  To gain a clearer understanding of these tropic dynamics, we have applied DNA-based molecular diagnostics to assess the diet of the Australian sea lion through the collection of faecal material from two geographically separated colonies in Southern Australia.  Given that individuals from each colony have specific foraging ecology; inshore-shallow and offshore geographic locations, these techniques demostrate high taxonomic resolution and a rich diversity of benthic prey that otherwise was obscured using traditional prey morphological identification techniques alone.  Coupled with the potential to assess Australian sea lion diet at a population level using these DNA techniques, this information is of significant importance given the paucity of dietary information for this species and the current IUCN listing as an endangered species.