Fishery independent surveys (FIS) of relative biomass and size have informed management of the South Australian (SA) commercial fishery for Latona deltoides (Pipi) for 18 years. Surveys are performed cooperatively between government and industry and provide estimates of relative biomass and sizes across the entire 60 km fishing ground at spatial scales of kilometres and metres and temporal scales of years, months and days. In April 2025, a harmful algal bloom (HAB), associated with an extensive and sustained marine heatwave, occurred in south-eastern SA and impacted the L. deltoides stock that supports the SA Fishery for this species. Fortuitously, the final sub-survey of 2024/25 FIS was completed 2 days prior to the first observations of mortality on the fishing ground. This final sub-survey was repeated 4 weeks later when the HAB appeared to have reduced. Between April and May 2025, mean biomass across the fishing ground had decreased by 36% with the largest reduction in the north-western 1/6th of the fishing ground. This impacted area was consistent with an area of elevated SST and Chl a, associated with the HAB. Biomass and sizes of L. deltoides present on the fishing ground before/after the HAB are considered within the context of the species’ life-history and to better understand the components of the population most affected by the HAB. Inter-annual variability in biomass of L. deltoides is well known and thought to be due to highly variable recruitment. In 2025, mortality associated with the HAB occurred when biomass was the highest recorded and size structures comprised multiple cohorts. While the HAB event in 2025 underlined the importance of adaptive monitoring to inform fishery management and TACC setting, resilience of this population to a similar mortality event when biomass is low, spatial distribution of biomass is different, and/or size structures comprise fewer cohorts is unknown.