Exploration

Threshers at dawn

We were surrounded. Round black eyes looking curiously at us from every direction. As the light current pushed us closer towards the watchful eyes, we were constantly checking in on each other - first to see if what was happening was real and second to make sure these encounters didn’t get any closer.

Words by Andi Cross
Photographs by Marla Tomorug

These creatures were granting us a close look at their incredible colouring and sensational heterocercal tails or caudal fins – the unique trait that gives the thresher shark its name. About a 45-minute ride off the mainland of Cebu in the Philippines, we found ourselves diving the spectacular Malapascua island, waking up at 4am to seek out the thresher sharks that call this area home. Known worldwide as one of the few locations where you can see threshers in the wild all year round, we knew this stop was a must on the Edges of Earth expedition trail. 

We wanted to understand why these elusive sharks can be found here, what it will take for this ocean to remain protected so that they continue to thrive and what we can do as divers to maintain the health of this ecosystem. All in order for other divers to experience this spectacle for years to come.

With so many sharks circling us, even during what’s classified as off season, we felt like we had hit the diving jackpot. Thresher sharks are deep-water dwellers – sometimes found at depths of 100-300 metres – which makes them rather challenging to see in the wild. Threshers go where the food is, and their main diet is squid, sardines and tuna, to name a few. 

But because of the ‘cleaning station’ located in Malapascua, it’s easier to spot threshers in much shallower water ranging from around 20-30 metres. A cleaning station is a specific location in the marine environment where fish and other aquatic animals come to be cleaned by smaller organisms, primarily cleaner fish or shrimp. These stations are vital to the health and wellbeing of marine animals and play a crucial role in the ecosystem.

Historically, a site called Monad Shoal was where most of the action happened in the Philippines. It’s a submerged seamount and sunken island that rises from the deeper waters surrounding it. This is where thresher sharks ascend from the depths at dawn to get their clean on. Parasites and dead skin are removed by the cleaner fish, particularly wrasse species.

Given the location’s depth and the typically avoidant nature of thresher sharks when it comes to human interaction, Monad was not always the easiest to dive. However, when we were there, Kimud Shoal became the main hangout for threshers. With larger animals making appearances at Monad – hammerheads, tigers and whale sharks – the threshers had changed up their location preference. 

Thresher sharks have long been calling Malapascua home. For centuries, local fisherfolk have been spotting these pelagic threshers breaching out of the water, fully displaying their bodies. The breach happens either because they are trying to get the parasites (copepods) off post cleaning, or because they are on the hunt. This is one of the ways fisherfolk could identify the threshers’ preferred locations, helping to point curious explorers in the right direction. 

Their fantastic and oversized tails are one of their most distinguishing features, also making them the formidable predators that they are. They’re used as a stunning device when hunting its prey by whipping them aggressively. This makes fish easier to catch and helps with precision during the hunt. However, what stood out to us even more were their huge, round, black eyes that have adapted to life in the dark, making them exceptional low-light hunters. 

Like many fascinating creatures on our planet, the pelagic thresher shark is classified as endangered by ICUN Red List of Threatened Species as of 2018. This status is predominantly due to habitat loss and climate change. Target fishing and bycatch are also factors when it comes to the thresher, making their low reproductive rate a significant issue for the species. Interestingly enough, the thresher shark will always give birth to a male and female and do not have a set gestation period. The reason why remains a mystery. 

Although there are no natural predators for the thresher and they are considered harmless to us, human activity is the driving factor for population decline globally. When in Malapascua, we met with technical diving experts – those who have been observing the pelagic species since 2010 throughout their dives. Matt Reed of Evolution Diving was our guy, and he and his team walked us through their long history of working to protect these animals in their natural habitat. Their protection method? Equal parts education on best diving practices and conducting citizen science. 

In 2014, the team utilised tagging technology and discovered a resident meta-population, revealing that these iconic creatures are not just passersby but inhabitants of these waters. This confirmed that the cleaning of the wrasse species – specifically moon wrasse and blue-head fairy wrasse – were keeping these sharks in the area. If the prevailing reef could no longer support these cleaner fish, it was noted the sharks might relocate to a more favourable location. 

With a reef that has seen some significant damage from the same threats that impact thresher sharks, so much of Evolution’s work is to help upskill divers. For as much as we think we’re not part of the problem, poor diving techniques can cause significant damage to the marine ecosystems we explore. Especially when diving happens repeatedly over many years in the same area. 

At Evolution, technical dive training takes centre stage, serving as a crucial pathway for divers to enhance their oceanic knowledge and diving expertise. Being the only dive centre capable of diving 30-100 metres (100-328 feet), this team has cataloged countless dives and seen threshers’ behaviour vary at different depths. Their ability to train divers to use multiple gasses enables people to see what happens when going beyond recreational dive levels.

While we were on-site, we worked with Matt to deploy a remote underwater video (RUV) to monitor shark activity at around 40 metres (131 feet.) By placing the RUV here, the team was able to document what happens as the sharks go deeper and deeper, as well as better understand their behaviours when humans are not present in the water.

So, what can we do as divers to protect the declining thresher shark species? Become better ones, continue our education journey and help others understand our role in safeguarding the planet’s natural wonders. It all comes down to the choices we make, the attention to detail we give on every dive and finding ways to contribute to citizen science programs if and when we can. 

Days out on the open ocean with Matt and his team sparked our desire to further educate. Ocean exploration is just as much about understanding our natural world as it is about understanding ourselves and the connection we have with the planet. Every dive is an opportunity to learn and observe, to understand the complex balance of marine life and our impact on it. 

Our interactions, our observations and our advancements in diving capabilities aren’t just for us – they serve a larger purpose of contributing to the ongoing narrative of ocean conservation. Each dive brings us closer to being active participants in preserving the beauty and health of the ocean.

If you want to level up, get smart on how to dive with conservation in mind and have one of the ultimate dive experiences of your life, hit up Matt and his team. And like the thresher shark after a wrasse cleaning, you might just come out the other side transformed.

 

Photographs by Marla Tomorug

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