Do Sharks Have Friends? What Moʻorea’s Reef Sharks Reveal

Do sharks have friends? The blacktips of Moʻorea keep long-term "preferred associations": some sharks choose each other's company again and again, in stable communities, and those partners are usually not family. Most of us grew up with the idea of the lonely shark, cruising the sea on its own. These sharks tell a softer and more complicated story.

But to study a shark's social life, you first need to know who is who.

Fins like fingerprints

For blacktip reef sharks, the black and white pattern on the dorsal fin, the big fin on the back, does this job. A study of young sharks around Moʻorea found that every shark's pattern is unique. The left and right sides are not the same, a bit like the two sides of your face.

The pattern also stays readable as the shark grows. In sharks caught again after periods of up to nine months, growth did not change it enough to stop identification.

So a clear photo of one side of a fin can be matched again and again, as long as it is compared with photos of the same side. With nothing more than a camera, researchers can follow one shark for years.

Do sharks have friends, or just neighbours?

Using these photos, researchers mapped which blacktips were seen together on Moʻorea's reefs. They found four main communities and two smaller subcommunities.

The sharks were not simply mixing at random. They kept long-term associations, even though they had chances to meet sharks from other communities. Sex and body length also played a part in who spent time with whom.

The researchers concluded that these groups were not just sharks gathered around the same food or the same shelter. They came partly from individual choice, which the scientists read as a sign of sociability.

Scientists are careful with words, so they speak of "preferred associations", not friendship. It is a quiet way of saying that some sharks keep choosing each other's company.

Friends, but not family

A natural guess is that these groups are families. DNA says no. When researchers combined their social maps with genetic tests, relatedness did not predict which sharks spent time together, neither between two sharks nor within a community.

The network was organised by place, but it changed over time. During mating periods, communities merged, and males seemed more sociable. The authors suggest that because blacktip mothers do not care for their young, family links may break very early in life.

Young sharks seem to work differently again. Juvenile blacktips around Moʻorea gather in their first stages of life, but these groups appear to be shaped by the environment, not by relationships.

Why learning sharks matter to you

There is more to that detail. When the removal in the simulations followed how easy each shark was to catch, the network kept its structure until up to 72% of the individuals were gone.

The researchers also added a warning for science itself. If animals learn to escape, population counts based on catching the same animals again can be biased.

One of the authors, Culum Brown, noted that it may surprise people that sharks have social networks too. Perhaps the bigger lesson is simpler. Experience seems to stay with a shark. If sharks learn from bad experiences, as the Moʻorea researchers suggest, then the way we behave in the water is part of what they learn.

Other sharks that read the room

Blacktips are not the only ones. Sicklefin lemon sharks are a solitary species, studied by researchers at CRIOBE, the research station on Moʻorea. In field experiments where sharks competed for bait, the more often two sharks had been seen together at a site, the fewer aggressive moments they had with each other.

Even a solitary shark, it seems, pays attention to who is around.

How to be a good neighbour in the water

Stay calm and flat in the water, keep your distance, and let the shark pass on its own path. Never chase, corner, touch or feed a shark. A low-volume mask that fits well helps me stay still at the surface instead of stopping to fix it, and stillness is the kindest thing you can offer. Wildlife encounters are unpredictable. Snorkelling near reef sharks should always follow local regulations and experienced professional guidance.

You can also help science. French Polynesia's citizen science network, the Polynesian Shark Observatory, gathered data from more than 13,916 dives across 43% of the territory's islands. A photo of a dorsal fin, taken from a respectful distance and without following the shark, can become part of that record. Ask your guide how to share it.

It is the same spirit we bring to lagoon and reef time on our Moʻorea retreat in September 2027: the animal chooses, and we watch.

Questions people ask

Wildlife encounters are never guaranteed and never forced. Ocean Calling works only with vetted, ethical local operators, and every animal is free to approach, or not, entirely on its own terms.