In the middle of the Atlantic Ocean, there's a tiny group of islands called the Saint Peter and Saint Paul Archipelago. It's a remote spot, but it's a hotspot for big, traveling fish like the yellowfin tuna. Scientists wanted to know if these tunas were born near the islands or if they just stop by on their ocean adventures.

To find out, they caught young yellowfin tunas over a year and studied their ear bones, called otoliths. These tiny bones grow like tree rings and hold chemical clues about where the fish have been. The scientists used a special tool to analyze the chemicals in the otoliths and compared them to the chemicals in the water where the tunas were caught.

They found something interesting. The chemicals in the tunas' ear bones didn't match the chemicals in the water around the islands. This means the tunas weren't born there. Instead, the scientists think the tunas come from places like the Gulf of Guinea and the Southern Cape Verde Islands. The islands might just be a pit stop on their long journey across the Atlantic.

The scientists also found that the tunas can be divided into two groups based on the chemicals in their ear bones. One group had more magnesium and copper, while the other had more zinc, barium, and strontium. Zinc was the most important chemical in telling these groups apart. It might show that the tunas passed by the islands on their way to somewhere else.

This study shows that the Saint Peter and Saint Paul Archipelago plays a big role in the lives of yellowfin tunas. It might not be where they're born, but it's an important place for them to visit. The scientists think the tunas use the islands as a stopover on their migratory routes. Other data supports this idea, showing that the tunas' journey is a complex one.

OTOLITH CHEMISTRY

Tuna Tales: How Tiny Ear Bones Reveal Big Ocean Secrets

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