Tracing Seal Predation Back to the Source Colony of Their Penguin Prey: A Trace Element and Stable Isotope Analysis

Marine predators recovering from historic, commercial, over-harvesting can create conservation challenges when they prey on vulnerable species. Pinniped predation of seabirds presents one such challenge and identifying the source colonies experiencing seal predation are needed to inform conservation management and decision planning. Here, we present a novel application of stable isotope and trace element techniques to identify the source colony of little penguins (Eudyptula minor) predated by long-nosed fur seals (Arctocephalus forsteri). We created baseline biochemical 'feather-prints' from feathers for six major breeding colonies across south-east Australia to compare with feathers from predated penguins recovered from seal scats. Feeding trials of captive seals confirmed that digestion of penguin feathers did not compromise stable isotope (delta C-13 and delta N-15) or trace element (Al, Ti, Sr and Mg) signatures. The resulting biochemical 'feather-prints' were found to be robust in being correctly classified to local sites (78%) and broader regions (85%). The distinguishing 'feather-prints' appeared to be driven by industrial inputs from land, colony-specific foraging patterns and potentially proximity to oceanographic systems (i.e. upwelling). Here, we show that 46-70% of predated feathers were assigned to 'local' penguin colonies. We consider that the regional penguin abundances and the proximity of their colonies to seal sites, as well as demographic-specific foraging patterns may shape their contribution to seal diet at local, regional and inter-regional scales. This diagnostic tool is powerful, having broad applications identifying seabird colonies at greatest risk to pinniped predation and informing targeted, site-specific, conservation effort.

Automated summary

A novel technique using stable isotope and trace element analysis was used to identify the source colonies of Little Penguins preyed upon by Long-nosed Fur Seals. This diagnostic tool proved to be robust, correctly assigning predated feathers to local sites and broader regions. The results suggest that regional penguin abundances, colony proximity to seal sites, and foraging patterns may influence the contribution of penguins to seal diet at different scales.