Marine protected areas can do more than guard what’s inside their borders — and Papahānaumokuākea is proving it. This vast Hawaiian reserve, spanning over 580,000 square miles, was created to protect biodiversity and culturally sacred Indigenous sites, not to boost commercial fishing. Yet catch rates for yellowfin tuna in surrounding waters rose 54%, a spillover effect driven by the monument’s sheer scale. The findings strengthen the global case for ambitious ocean protection, arriving just as momentum builds toward safeguarding 30% of the world’s oceans by 2030.