Tuna Tales: How Tiny Ear Bones Reveal Big Ocean Secrets

In the vast expanse of the Atlantic Ocean lies a remote gem, the Saint Peter and Saint Paul Archipelago. This tiny group of islands is a haven for yellowfin tunas, but scientists have long wondered if these fish are born here or merely passing through.

Unraveling the Mystery

To solve this puzzle, researchers caught young yellowfin tunas over a year and studied their ear bones, known as otoliths. These tiny structures grow like tree rings, holding chemical clues about the fish's journey.

Using a special tool, the scientists analyzed the chemicals in the otoliths and compared them to the water around the islands. The results were surprising:

• The chemicals in the tunas' ear bones did not match the water around the islands.
• This suggests the tunas were not born in the archipelago.
• Instead, they likely come from places like the Gulf of Guinea and the Southern Cape Verde Islands.

Two Groups of Tunas

The study also revealed that the tunas could be divided into two distinct groups based on the chemicals in their ear bones:

• Group 1: Higher levels of magnesium and copper.
• Group 2: Higher levels of zinc, barium, and strontium.

Zinc was the key chemical that set these groups apart, hinting that the tunas might be using the islands as a stopover on their way to another destination.

The Archipelago's Role

This research highlights the Saint Peter and Saint Paul Archipelago as a crucial stop for yellowfin tunas. While it may not be their birthplace, it serves as an important pit stop on their migratory routes. Other data supports this idea, showing that the tunas' journey is far more complex than previously thought.