Fossil shark denticles reveal Panama reef baselines

A study published in Science, led by Erin Dillon and co-authored by researchers from the University of California, Santa Barbara and the Smithsonian Tropical Research Institute, used fossilized shark dermal denticles (shark 'dandruff') preserved in reef sediments to reconstruct historical shark abundance on both coasts of Panama. Comparing sediments from 7,000-3,000 years ago with those from the past century, the team found that before intensive fishing, reefs in the Gulf of Panama supported roughly 20 times more sharks than Caribbean reefs, despite being only 100 km apart. Caribbean denticle accumulation fell by about 75%, while Pacific rates remained statistically unchanged from prehistoric baselines, resulting in Pacific reefs now yielding about 100 times more denticles. The difference is attributed to ocean productivity: the Pacific benefits from seasonal upwelling, while the Caribbean is nutrient-poor. The findings caution that conservation targets based on the wrong baseline could be off by an order of magnitude, and that ocean productivity must be considered alongside fishing history. The authors also note that Pacific sharks face recent pressures from intensified fishing since the 1980s and a record failure of upwelling, potentially pushing them into unprecedented conditions.