Extreme climatic events are a critical manifestation of climate change and recognised as a driving source of ecological change. Marine ecosystems are strongly influenced by such events, including marine heatwaves which directly impact ecosystem structure and deplete biodiversity. In 2011, Western Australia experienced an unprecedented marine heatwave that caused catastrophic damage, including the largest loss of seagrass biomass globally. To determine the effect of the heatwave on the resident population of Indo-Pacific bottlenose dolphins (Tursiops aduncus), we used 18 years of observational data, including 9 years pre-and post-heatwave. We found that the dolphins (N=51) significantly decreased their home range area (average reduction = 33km2) and shifted south-east, further inland within the bay. Sex differences were present, where males experienced larger home range shifts and decreased area (average reduction M=55km2, F=15km2). This suggests females are poorly adapting to environmental change, likely explained by differences in biology and home range inheritance between sexes. Overall, our results highlight the importance of further investigation into sex differences when assessing extreme climatic events. This work will aid in our understanding of how species adapt to human-induced global warming and help predict future ranges in response to the expected increase of extreme climatic events.