Environmental correlates of temporal variation in the diet of Australian fur seals

Long term systematic monitoring of the diet of large marine predators can be an effective approach to detect and understand changes in ecosystems vulnerable to environmental change. This study quantified seasonal and annual changes in the frequency of occurrence (%FO) of prey items in the diet of Australian fur seals (Arctocephalus pusillus doriferus) in Bass Strait from 1998 to 2014. Using hard part analysis, 71 prey species were identified, with combinations of 8 main species found in more than 70% of the samples. Otolith measurements suggest Australian fur seals consumed predominantly juvenile fishes. I investigated correlations between environmental variables and %FO using generalised additive models. Southern Oscillation Index (SOI) correlated with the %FO of red cod Pseudophycis bachus, pilchard Sardinops sagax and jack mackerel Trachurus declivis. Positive correlations relating to El Niño conditions were found for both red cod and pilchard and correlation with neutral SOI was found for jack mackerel. Correlations identified between long-term environmental change and prey of marine predators suggests large-scale processes can influence prey assemblages at various trophic levels in Bass Strait.