Thresher Shark Study 2025: Why a Few Females Matter

Fifteen to eighteen. It sounds like a small number, and in the wrong headline it could sound like a tragedy that already happened. A 2025 study of pelagic thresher sharks in the Central Visayan Sea found that, in its population model, removing 15 to 18 females could lead to a decline. That is not a report that those sharks were killed. It is a warning from a model about how sensitive a slow-growing shark population may be to fishing pressure.

The research matters for Kimud and Monad, because these shoals are among the rare places where divers can watch pelagic threshers at cleaning stations.

The camera that measured without catching

Researchers placed a remote stereo-camera system at Monad Shoal to measure pelagic threshers. Two cameras record the same animal from slightly different angles, and software uses the paired images to estimate its size. This way, scientists can learn about the sharks' age and size structure without catching or handling a single animal.

The study used four months of observations, from December 2019 to March 2020. That detail matters. This was a focused survey and a modelling exercise. It was not a live count of every shark in the Central Visayan Sea.

What does the "15 to 18 females" figure really mean?

The researchers put their size data and life-history estimates into a population model. Under one hypothetical fishing-mortality scenario, the model showed how vulnerable the population could be. Removing 15 to 18 females was linked with decline.

Pelagic threshers grow slowly and have relatively few pups. If adult females are taken away, fewer animals are left to reproduce.

But the study does not say that 15 to 18 females were actually taken. It does not say that Kimud alone has that many sharks today. The finding describes a modelled risk for the regional population.

Why tourism and monitoring belong in the same story

The scientists said that non-invasive monitoring can help fill gaps where fishing data are incomplete. At the same time, these shoals support dive tourism and local livelihoods.

The goal is not to turn one dramatic number into a scary headline. It is to understand what the animals need and to manage human pressure around that.

At Kimud, give the sharks room to use the shoal and its cleaning stations. A quiet observation is better for the encounter and better for the data.

Wildlife encounters are unpredictable. Diving with thresher sharks should always follow local regulations and experienced professional guidance.

Read our Philippines ocean guide for more on the country's marine wildlife places.

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.