The Mesolithic-Neolithic transition is a classic topic of archaeological discussion, and the East Adriatic is of particular interest as a gateway region for agriculture entering Europe from the Near East. Neolithisation along the East Adriatic coast has been characterised as a two-wave process of leap-frog demographic replacement along the Dalmatian coast, followed by a longer process of acculturation further inland. Research on this transition primarily addresses the arrival of Neolithic technology and domesticates, but the view from ‘traditionally Mesolithic’ activities can provide an alternative perspective. This pilot study highlights one such practice, identifying changes in the seasonality of shellfish gathering over the Neolithic transition using material from Vela Spila, Korčula (Croatia). Specimens of the gastropod Phorcus turbinatus from across this transition were assessed using oxygen isotope analysis. Results showed a focus on summer and autumn collection during the Mesolithic, which then shifted to autumn and winter in the Neolithic. These results indicate differences in shellfish gathering and exploitation across the Neolithic transition, and implications for the demographic transition and human-environment interactions are discussed. Shellfishing in the East Adriatic is identified as an area of Neolithisation rather than Mesolithic continuity.