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There are few places in the ocean where hammerhead sharks still congregate in large numbers and a recent prolonged warm water cycle pushed them to swim deeper than humans can safely dive.
But with the arrival of cooler waters they are now gliding back towards the surface.
Scalloped hammerhead sharks (Sphyrna lewini) can be spotted peacefully making their way through the deeper waters surrounding the volcanic Cocos Island off Costa Rica.
Underwater photographer Adriana Basques travelled to the diving spot, hoping to capture something special on camera - and she wasn't disappointed.
Adriana's photograph, Hammerhead, was one of the 24 images shortlisted for the Wildlife Photographer of the Year 53 People's Choice Award.
Cocos Island is known for its diving sites, most of which range between 24 and 33 metres in depth. The island became a national park in 1978 and its waters a marine protected area in 1982, making it a safe haven for life underwater.
The island is located around 560 kilometres off the coast of Costa Rica. Although the bounty of congregating hammerhead sharks may appeal to photographers, the location can make for a challenging expedition.
Adriana explains, 'The currents are often fierce and the visibility can be unpredictable. It can be difficult with a large camera rig.'
Additionally, a warm water cycle known as El Niño had lasted longer than usual, posing further difficulties for photographers. Hammerheads prefer cooler water and will swim as deep as 275 metres in search of it.
'Over the last several years, due to a longer-than-usual El Niño cycle, sharks disappeared into the deeper waters beyond the recreational diving limits,' says Adriana.
But in the last year, the waters have begun to cool again, entering the cooling La Niña phase of the El-Niño - Southern Oscillation (ENSO) cycle.
ENSO is an irregularly occurring fluctuation in surface water temperature and atmospheric pressure in the eastern Pacific Ocean. The warm El Niño and cold La Niña episodes usually last from nine to 12 months, although they can sometimes last years.
Changes in water temperature affect animals living below the surface, but also have an impact on weather and climate.
The arrival of La Niña meant the return of the hammerheads.
Adriana says, 'After a 36-hour crossing, which can be uncomfortably rough, we arrived to find that the sharks were now seen at depths that were once again accessible.'
Despite their fearsome reputation, sharks appear wary of the disturbance that visiting divers create.
'In general, sharks tend to not like the bubbles from scuba tanks and are predisposed to hang back from the noise and commotion scuba diving creates,' Adriana says.
'Getting close requires an exercise in patience and slow breathing, especially when they get curious and begin to come closer.'
Thanks to a sunny day with natural light and good visibility in the water, Adriana descended into the sharks' realm.
'I could see the sharks begin coming in closer to check out who the interlopers were as they circled back and forth around the sea mount, moving in and out, above and below.
'Fortunately the sharks were as curious of us as we were of them. We encountered several large schools that paraded around, with some individuals coming close enough for me to build an image.
'From out of the school one particular shark strayed in my direction to have a look, just long enough for me to hunker down, staying low and capturing a full-frame image with the school of cottonmouth jacks in the background.'
In its brief glide past Adriana, the hammerhead shark appeared to flash her a toothy grin.
Adriana says, 'I am particularly fond of this image because the shark lends the appearance of a little smile.
'Though we know that sharks don't smile, it helps to form an anthropomorphic point of view, to give people a level of comfort and to begin to understand that sharks are not the demons of the deep that movies and news feeds often portray them as.
'Sharks are indicators of the overall health of the ocean. They feed on the dead, the dying and the diseased.
'They have served in this role for millions of years and yet, each year, millions of them are hunted and killed to sustain the desire of making a bowl of soup, or due to ignorance and fear.'
As an underwater photographer, Adriana shares what she sees in the ocean with those who may not have the opportunity to see it for themselves. She feels it is her duty to help educate the public on the importance of sharks.
'They are the sanitation managers of our oceans,' explains the photographer.
'As we look upon the ocean, I can understand that for most people the surface merely represents the skin of our planet. But the ocean makes up more than 75% of the surface of Earth and what happens beneath that skin is what helps keep humanity alive.'
'I want to bring attention to how beautiful and necessary our oceans are and how sharks are part of the web of life that keeps everything in balance.'
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