Knowledge of the 3-D structure and variability of ocean temperature is critical for understanding ocean circulation, heat uptake and marine extremes, as well as the abundance and distribution of marine life. While satellite technology offers near-global coverage of surface ocean temperatures, sub-surface observations are still the biggest gap in the ocean temperature record. Here we present first results from FishSOOP; Australia’s pilot program using commercial fishing gear to collect sub-surface temperature data. Operating since early 2023, we have collected temperature data across the breadth of Australian shelf seas revealing insights into the development of marine heatwaves throughout the water column. Comparison with the SEA-COFS ocean forecast models shows the potential for improving forecasts of upper ocean heat content and bottom temperatures by filling the gaps in observational data coverage. We will also share new results of observing system simulation experiments that quantify the benefit of subsurface temperature observations on ocean temperature metrics from data assimilating models. FishSOOP has driven a step-change in the amount of open access temperature data available at low cost and provides critical information on sub-surface temperature metrics, essential for future proofing marine industries.