Ecological science increasingly recognises that positive interspecies interactions — mutualism, facilitation and symbiosis — are as fundamental to ecosystem health as competition and predation. For Aboriginal peoples of southeastern Australia, this understanding has been encoded in knowledge systems built within and around nature's patterns for tens of thousands of years. In Aboriginal metaphysics, the symbiotic relationships between people and their marine kin — dolphins, whales and sharks — are carried in story, song, dance, ceremony and cultural practice, constituting a governance system as much as a knowledge system. This paper draws on the Unbroken Whispers: The Ripples Connecting Sea Kin project to explore Aboriginal symbiotic relationships with dolphin and whale kin, examining how relational metaphysics encode and sustain interspecies mutualism and what this means for marine conservation. It argues that restoring the conditions for custodial cultural practice restores the conditions for the symbiotic relationships that have sustained southeastern Australia's marine ecosystems across deep time.