It is easy to wonder how many sharks would have been here before humans began fishing our ocean intensively. A few dozen more? Hundreds? But how would we even know? For most marine ecosystems, there is no historical survey telling us what a truly intact shark population looked like. And if we do not know what “healthy” looked like before major human impacts, how can we know how far populations have fallen, or what recovery should look like? Well, a new study from Panama offers an unusual way to answer that question: look down.

Instead of relying solely on modern surveys, researchers examined the tiny fossil dermal denticles that cover a shark’s body; like fingerprints, these microscopic scales can carry information about the kinds of sharks that lived in an ecosystem. When sharks lose these scales, they can accumulate in sediments on the seafloor. Some remain preserved for thousands of years, creating a kind of biological archive. So in this study, researchers analyzed 3,497 denticles from 157 sediment samples collected on both sides of the Isthmus of Panama, regions that are geographically close but environmentally very different (Bocas del Toro on Panama’s Caribbean coast and the Gulf of Panama on the Pacific side). They looked at sediments from the mid-Holocene, roughly 7,000 to 3,000 years ago, before intensive human exploitation, and compared them with sediments representing approximately the past century. This gave them a baseline that goes beyond the earliest fisheries records or the first scientific surveys, reaching back thousands of years.

What they found was striking — over the following millennia, the two regions moved in very different directions. In the Caribbean, shark denticle accumulation declined by about 75% compared with the mid-Holocene baseline, meaning that sharks were estimated to be roughly four times more abundant before intensive fishing began. The decline was especially pronounced among pelagic sharks, including species groups such as requiem sharks and hammerheads that are often targeted by fisheries. Demersal sharks also became a larger proportion of the remaining community, but before you get excited, you should know that that does not mean their populations were thriving. Their absolute abundance also declined substantially. Pacific Panama, on the other hand, tells a very different story. Before substantial human impact, Pacific Panama’s reefs supported roughly 20 times more sharks than Caribbean reefs and shark denticle accumulation remained comparable to mid-Holocene levels. Pelagic sharks continued to make up more than two-thirds of the denticle assemblage, and the overall structure of the shark community did not significantly change across the millennia represented in the sediment record; this is particularly fascinating because Pacific Panama has historically experienced more than 95% of Panama’s fishing pressure.

So, how could sharks appear relatively resilient in the place experiencing greater fishing pressure while Caribbean sharks declined under lower levels of fishing? The researchers point toward oceanography for part of the answer. Pacific Panama experiences seasonal upwelling, when cold, nutrient-rich deep water rises toward the surface. Those nutrients fuel the base of the food web, supporting more phytoplankton, more fish and ultimately more energy available to large predators. The Caribbean, by comparison, is more oligotrophic, meaning its waters contain fewer nutrients. The difference between the two regions gets amplified as energy moves through the food web, resulting in substantially greater fish biomass in the Pacific. In other words, the Pacific may simply have had a much larger ecological “budget” for supporting sharks.

The team argues that these new findings should change how we think about setting conservation targets. Assuming that two regions with similar shark species have the same carrying capacity could lead us to underestimate what one ecosystem is capable of supporting and be biologically unrealistic. Thus, they argue that environmental context needs to be considered alongside shark life history, fishing pressure, habitat availability and connectivity. Not only that, but that "resilient” does not, and should not, mean “safe,” and the researchers are careful not to suggest that Pacific shark populations are immune to human impacts. The fossil record provides a long-term view, but because the most recent samples span roughly the twentieth century to today, declines that occurred during the most intense period of modern shark fishing may be difficult to detect. The broad ecological categories used to classify denticles can also mask changes in individual shark species; in fact, fisheries data indicate that some Pacific shark populations have become increasingly unstable since the early 2000s. The long-term record appears to show that Pacific Panama has historically had a high capacity to support large shark populations and that capacity may have buffered sharks from past pressures, but it does not guarantee that they will continue to withstand increasing fishing pressure and other environmental changes.

It is important to remember that modern ecosystems are snapshots, and sometimes they are snapshots of ecosystems that have already been heavily altered. Fossil records give us another view of this modern-day captured moment, revealing ecological changes that happened long before scientists started counting sharks. But what happens when the environmental conditions that once buffered a population begin to change too? Climate change is expected to reduce ocean productivity in parts of the Tropical Eastern Pacific, potentially weakening the very ecological conditions that have helped sustain its sharks for millennia. If productivity falls while fishing pressure remains high, could a population that once seemed resilient cross a threshold into rapid decline?

Those are difficult questions, but they are exactly the kinds of questions that long-term ecological records allow us to ask. A tiny shark scale sitting in ancient reef sediment might seem insignificant, yet thousands of those scales — all layered through time — can tell us not just how many sharks we have lost, but what the ocean was capable of supporting before we changed it. Perhaps that is the baseline we need to build a smarter future for sharks. This new study is a great argument for just that.