Understanding the relationship between spawning sites (sources) and the reefs (sinks) where larvae settle is pivotal for effective species management. Traditionally, work on larval dispersal and connectivity between regions is used to highlight crucial source areas, with an overall aim to bolster spawning biomass. However, for over-abundant species like the Longspined Sea Urchin, priorities are flipped. Our study identifies key source regions within Australia and how their relative contribution to the Tasmanian stock changes over time, with an aim to minimize spawning stock or pinpoint and prevent potential stepping stone areas for further range extension in Tasmania. We analyse larval dispersal to and from Australian reefs over the past three decades (including to New Zealand) considering temperature, factors such as diel vertical migration, and scaling by biomass estimates at source reefs. Our findings outline critical pathways, offering actionable insights for management.