Kelp forests are important temperate marine habitats that support biodiversity and sustain commercial fisheries. High abundances of sea urchins can create urchin “barrens”, which are low-productivity areas where all kelp has been grazed. In south-eastern Australia, urchin barrens caused by the urchin Centrostephanus rodgersii are a major feature of the coastline and are increasing in some areas. Fisheries in New South Wales and Tasmania harvest urchins for their gonads, however urchins from barrens are thought to have limited access to food resources which can result in unsaleable gonads. We used in situ surveys to investigate how gonad size, gonad quality and morphology vary with depth and distance from kelp across 700km of the NSW coast, and used stable isotope analysis to compare isotopic signatures of urchins and potential diet items. We found significant effects of distance from kelp and depth on urchin roe quality, gonad index and morphology. Urchins from Sydney occupied the widest isotopic niche space, and kelp was the main contributor to urchin muscle tissue across regions. Our findings can inform new potential harvest areas for urchin fisheries in kelp-depleted areas, which can contribute to kelp conservation, job creation and fisheries development.