Striped marlin use a quick color change to signal an attack

Striped marlin, some of the ocean’s fastest and fiercest predators, work together to hunt prey. But how do they avoid colliding with each other in the frenzy of the chase? A new study from the Humboldt University of Berlin reveals a surprising secret: rapid color changes.

Life and habitat of striped marlin

Striped marlin are impressive fish found in warm and temperate waters of the Pacific and Indian Oceans. They are easily recognized by their blue and black stripes that become more prominent in certain events. 

These fast swimmers, reaching speeds of 50 miles per hour, use their long, pointed bills to slash through schools of smaller fish like sardines and anchovies, stunning them before eating. Their tall dorsal fin and streamlined body help them chase prey efficiently. Adult marlins can grow up to 12 feet long and weigh up to 450 pounds.

Striped marlin live in the open ocean near the surface and are constantly on the move, traveling long distances for food and breeding. They are mostly found off the coasts of Mexico, California, New Zealand, and Australia.

Striped marlin on the attack

Using high-quality drone footage, scientists were able to observe striped marlin behavior in never-before-seen detail. They discovered a remarkable phenomenon: the stripes on the marlin’s body lightened dramatically during an attack on prey, then returned to normal afterward. 

This change in brightness wasn’t observed in marlin that weren’t hunting, suggesting it might be a way for them to communicate with each other during the hunt. 

“We found that the attacking marlin ‘lit up’ and became much brighter than its group-mates as it made its attack before rapidly returning to its ‘non-bright’ coloration after its attack ended,” explained Alicia Burns from Humboldt University of Berlin.

Basis of the color change 

Striped marlin can change colors due to a few special cells in their skin called iridophores. These cells contain crystals that reflect light, allowing the marlin to go from a blue-gray to showing bold stripes. 

This strategic color change happens mainly when striped marlin hunt in groups, and it serves several purposes. First, it helps them communicate with each other. By making their stripes brighter just before attacking, marlin signal that they’re going in, which helps organize the hunt and prevent them from bumping into each other. 

Furthermore, the color change might keep other marlin away from their prey. This would be important when there are many predators competing for the same food.

Marlins with bolder stripes

The study also suggests the color change might confuse the fish that are being hunted. The sudden appearance of bold stripes could make it harder for the fish to escape together. This idea is supported by the fact that marlin attacking schools of fish underwent significantly greater color change compared to marlin that were attacking individuals. 

“Color change is widespread in animals, often multi-functional, and is likely to be more common in predators than is commonly reported,” wrote the study authors. 

“When groups of marlin make high speed, sequential attacks on the same prey target, they dynamically change color in relation to the timing of their attack. Thus, the intensity of marlin’s color contrast appears to be a reliable cue of their intent to attack.”

Many questions remain

The researchers are excited to learn more about how and why marlins change color. They have several questions they want to answer, such as:

Do marlins change color in other situations? The experts wonder if the rapid color changes seen during group hunting also happen when marlins hunt alone. This would help them understand if this is a general skill or specific to group dynamics.

Do other predatory fish use similar tactics? This question looks beyond marlins to see if their strategy is unique or if other predatory fish use similar color-changing tactics to hunt. 

“We already have footage of hunting behavior of sailfish and mahi mahi where we have seen even more pronounced and more variable color change than in the marlin,” explained Dr Burns.

By answering such questions, the experts hope to understand the full purpose of the flashing stripes. This could reveal a lot about how predators and prey interact in the ocean and how marlins have evolved to be such successful hunters. 

The study is published in the journal Current Biology.

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