Two oceans, one country—and 20 times more sharks in the prehistoric Pacific
How many sharks should a coral reef have? It sounds like a simple question, but almost nowhere on Earth is there a reef that has not at some time been fished or otherwise affected by humans, so there is no yardstick against which to measure what has been lost or what recovery would look like.
Researchers at the Smithsonian Tropical Research Institute in Panama discovered that the Pacific coast of the Isthmus of Panama once supported roughly 20 times more sharks than its Caribbean counterpart, despite both regions being fished. The key to this revelation lies in shark "dandruff" – tiny tooth-like scales called dermal denticles that sharks shed continuously and settle into reef sediments.
By counting these denticles in well-dated sediment samples, scientists can estimate the number of sharks that swam over the reef at that time. The study found that Pacific coast reefs have maintained shark populations at near prehistoric levels, while Caribbean reefs have experienced a 75% decline in shark accumulation. This discrepancy is attributed to differences in oceanic conditions – the Gulf of Panama, on the Pacific coast, is highly productive due to seasonal upwelling that brings nutrients to the surface, supporting large predator populations.
In contrast, the Caribbean coast is more nutrient-poor, resulting in lower shark abundances that are more vulnerable to fishing. The findings highlight the importance of considering ocean productivity, not just fishing history, when setting conservation targets for shark populations.
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