Prehistoric shark scale findings offer insights into the abundance of coral reef predators before human disturbance

In a groundbreaking study, an international team of researchers, led by UC Santa Barbara ecologist Erin Dillon, have used a unique method to delve into the past and uncover the dramatic decline of shark populations in Caribbean Panama over the last century.

The team's focus was on shark scales, a valuable resource for paleo-ecologists as they offer much more material for analysis compared to teeth. By applying this technique to the more recent past, Dillon and her colleagues have shed light on the history of shark populations in the region.

Historical accounts and the fossil record suggest that most of the shark declines in this location occurred within the past 100 years. The team's analysis revealed a 71% decrease in total shark abundance between the mid-Holocene and the present day.

The study compared the abundance and variety of shark scales from a Panamanian coral reef 7,000 years ago to those in reef sediments today. Swifter-swimming species took a harder hit in the decline of shark abundance, with midwater swimmers like requiem and hammerheads declining more than demersal species like the nurse shark.

If fishing were the only driver, a significant drop in nurse shark numbers wouldn't be expected due to their low commercial value. However, the study found declines in all shark types, suggesting that other factors may be at play.

Dillon and her colleagues are collecting sediment cores from regions with different human and ecological histories to track high-resolution trends in scale types and abundances over the last several millennia. They hope that other researchers will take advantage of this powerful technique and apply it to other locations around the world.

The study provides insight into shark ecology and offers context for the numbers of sharks observed on reefs today. Dillon plans to continue investigating dermal denticles, studying variation in the rates at which different shark species shed their scales.

This research underscores the urgent need for conservation efforts to protect shark populations, which have plummeted worldwide since records began in the mid-20th century. As Dillon notes, "Understanding the past can help us better understand the present and plan for the future."

Prehistoric shark scale findings offer insights into the abundance of coral reef predators before human disturbance