Prevalence of invasive fish and plants in the winter diet of the rakali (Hydromys chrysogaster)

Understanding the dietary components of a species can help reveal complex ecological interactions within an ecosystem. We analysed the diet of a native semi-aquatic predator, the rakali (Hydromys chrysogaster), to investigate its reported preference for invasive species in a regulated freshwater system. We used faecal metabarcoding analysis to identify key dietary items consumed during winter in the Yanco Creek System of southern New South Wales. While rakali did not display a significant difference in the consumption of invasive and native fish, 79.5% of total fish relative read abundance were invasive. The common carp (Cyprinus carpio) comprised 16.8% of the total diet relative read abundance and was present in 78.6% of samples. Plant matter was present in all samples and over half of the total relative read abundance of the diet. The prevalence of plants in the winter diet of rakali indicates that they are an important dietary supplement when other resources are limited. We show that the prevalence of invasive fish consumed by rakali is likely a result of their greater abundance in the system, rather than a direct preference. Further research is needed to determine the extent to which rakali can control invasive prey populations.