Fossil denticles reveal how ocean productivity shapes shark baselines and recovery potential

Shark populations on coral reefs have declined globally, but few baselines exist to quantify natural variability before human impact. Using fossil dermal denticles preserved in reef sediments, we reconstructed shark communities across the Isthmus of Panama before substantial exploitation [~7 to 3 thousand years ago (ka)] and recently (past century). We found differences in shark baselines and responses to fishing between the oceans on either side of the Isthmus. Reefs in the Pacific supported an ~20-fold higher shark abundance than Caribbean reefs before human impact. Caribbean shark populations—particularly pelagic species—have declined by 75% since the mid-Holocene, whereas their Pacific counterparts persisted over millennia despite higher fishing pressure. These contrasting trajectories are consistent with differences in oceanic productivity that dictate regional carrying capacities, highlighting the importance of incorporating oceanographic context into marine conservation targets.