Conserving dolphins in the Swan Canning River System: an ecosystem based approach

Bottlenose dolphins are valued feature of the Swan Canning river system. Sighting data indicate that dolphins use the rivers year-round and range throughout their extent. The 2009 mortality event emphasised the need to improve our understanding of the connections between dolphins and the estuary ecosystem. We address three elements of an ecosystem-based approach to dolphin conservation: (1) environmental influences on dolphins; (2) interactions between dolphins and other biological components; and (3) dolphins as a means to increase community understanding about river health. To investigate environmental influences, we are investigating: (a) the prevalence and severity of tattoo skin disease lesions on known dolphins from the river system and adjacent waters (e.g. Cockburn Sound); (b) spatial and temporal patterns in lesion occurrence; and (c) associations with salinity and other environmental factors. A preliminary investigation into dolphin foraging ecology in 2009 indicated differences between the stable isotope ratios of dolphins associated with the river system and dolphins associated with two coastal sites, and also supported behavioural observations indicating that dolphins associated with the river system are likely to feed on both marine and estuarine-based prey. Climate change and population growth will continue to alter the Swan Canning river system, suggesting that the long-term retention of dolphins as functioning ecological components of this ecosystem will on-going adaptation and change, both by dolphins and by human managing the environment around them