Long-term trends in habitat use and site fidelity by Australian humpback dolphins Sousa sahulensis in a near-urban embayment

ABSTRACT: Habitat use and site fidelity in coastal dolphins can vary in space and time, and are important components in conservation planning and predicting the impacts of environmental change. Little is known of long-term patterns of habitat use and site fidelity in threatened tropical delphinids. Here, we investigate trends in habitat use and site fidelity of Australian humpback dolphins Sousa sahulensis in Moreton Bay, a near-urban embayment in Queensland, Australia, using spatially referenced sightings from systematic surveys and government datasets. Data from 1992 to 2016 were assigned to 3 time periods with similar spatial coverage and compared using ecological niche and kernel models. We also used behavioural data collected from 2014 to 2016 to investigate the potential ecological function underpinning recent habitat preferences. A long-term fidelity and consistency in habitat use was evident at an industrialised port at the mouth of the Brisbane River, but patterns of habitat use were more dynamic elsewhere. Models of spatial patterns of behaviour suggested that areas used consistently were mostly foraging habitats. A marked shift in habitat use away from the northwestern side of Moreton Bay was evident after 1999, which we suggest was due to a decline in habitat integrity exacerbated by periodic floods. Our results imply that the optimal conservation strategy for the species would be to focus on areas that are long-term core habitats, whilst safeguarding against environmental change by maintaining habitat integrity across the broader area delineated by their ecological niche.