Dr Mark Meekan, Senior Research Fellow at the Oceans Institute, University of Western Australia, is a whale shark expert. Which is just as well, because what I watch him do, on video, is gobsmacking. Wearing a wetsuit, weight-belt, mask, snorkel and fins, Mark slides into the ocean on Australia’s Ningaloo Reef / Nyinggulu. He dives a few metres to where an eight-metre juvenile male whale shark swims, unconcerned by his presence. Mark equalises his ears, reaches down and gently touches the lips of the shark. Far from alarmed, the shark slows, appears almost hypnotised. Mark tips the shark upwards and eases it towards the surface. “As far as he’s concerned, I’m a big clumsy cleaner fish,” Mark says. “I scrape parasites from his lips for microscopic analysis, while he sits there and enjoys the clean.”

In 1998, Mark Meekan was working as a fisheries biologist, collecting swarms of krill around Exmouth Gulf. It occurred to him that the whale sharks, which he had seen gathering in numbers during March until August on Ningaloo Reef, were after the same food source, so it might be simpler to find them instead. He was soon applying for money to tag and track 60 sharks in order to learn more about their migratory patterns. He’s been researching them ever since. “Tagging is so much more sophisticated now, we can see where the sharks are at different depths, and for how long, get information on body temperatures, even tail beats and body movements.”

Ningaloo is a fringing reef, meaning it lies close to shore – barely 100 metres in some places. Beginning by the town of Exmouth, it runs south for 260 kilometres before petering out at Amherst Point. It is easily accessible to humans, but Ningaloo’s geographical positioning, off the northwest coast of Australia, has thus far protected it from elevated levels of human activity.

Whale sharks are filter feeders. According to Mark, this makes them a perfect indicator species. “They’re harvesting everything that’s out there, not just plankton and varieties of small fish, but plastics, strands of ghost nets. They provide information about the productivity but also the problems of the oceans.” Mark uses a small ultra-sound too, swimming beneath a shark and running the machine along its belly, examining it internally without disturbing it. Typical of human innovations put to imaginative uses, these small, water-proof devices were originally developed for UK veterinarians who have to work with farm animals in sometimes wet and muddy fields.

Whale sharks are quite well-studied, thanks to identifiable gatherings of individuals in shallow waters. Even so, much about their breeding cycle is unknown. “The biggest females grow to 18 metres. We think they are sexually mature at 30 or 40 years of age, but we still don’t know where they breed, presumably places out in the deep ocean,” says Mark.

Female whale sharks are ovoviviparous: they produce eggs, which then hatch inside the body before the pups mature and the female gives birth. No-one has ever recorded seeing a whale shark give birth. Much studied is the case of ‘Big Mama’, a female whale shark caught in 1995 by a Taiwanese fishing net. 300 embryos, at various stages of development, were inside. Only 14 were kept, frozen, for scientific analysis. As Mark explains, female whale sharks can retain sperm, a sort of reproductive insurance policy. “The fourteen embryos we were able to study were fertilised by a single male, so the conclusion was that all 300 may well have been too.”

The current global population is only a guesstimate, in the range of 100,000 to 300,000 animals. Whatever their actual numbers, researchers believe that there has likely been a 50% decrease in the last 30 years. While they are a target for some fisheries, whale sharks are most at risk from boat-strike incidents. “In the deep ocean, juveniles and adults of both sexes will dive to five hundred metres to filter for plankton. But there is a steep metabolic penalty they pay for being in water this cold and this deep. They have to warm up after a dive. So, you have this giant animal, swimming slowly, at or near the surface, where much of the world’s trade is transported in huge container ships travelling at twenty-five knots. Ship strike injuries on whale sharks are common, and often fatal,” adds Mark.

To see them for myself, I join a whale shark boat tour, which run late March to August from the town of Exmouth. When the skipper gets word from a spotter-plane pilot that a shark has been sighted, he sidles up as close as he’s permitted and our first group of 10 snorkellers is scrambled into the water.

Over the next two hours, we swim alongside five different sharks, all six to seven metres long. I’d anticipated this would be a thrilling experience, but in fact it’s a revelation: the flat head and wide mouth are as expected, and the whale shark is commonly said to be “the size of a school bus”; but there the bus comparison ends. Starting behind the pectoral fins and running down to the tail are three sharp ridges, with one atop as well.

These ridges slice through the ocean, almost visibly peeling water away as the shark swishes effortlessly along. I’m finning like mad and no hope of keeping up. Perhaps having a head built for filter-feeding is offset by having a body akin to that of a fighter-jet, built for speed. Evolution appears here to have done an impeccable job.

But it is the spot markings that have me mesmerised. Swimming alongside, these are ghostly white, and the last thing visible as the shark vanishes into the gloom. Photographed from above, they appear more like a constellation of stars and planets, twinkling with the shark’s movements and changes in the light. It’s apropos therefore that a citizen science identification and tracking system, based on each animal’s unique markings, borrows from a method used to map the night sky. Divers, snorkellers, amateur photographers, drone enthusiasts, in over fifty countries, have submitted photographs of whale sharks that feed into a world-wide database. All this data necessitated a clever algorithm to make analysis of it speedy and efficient, so software expert Jason Holmberg and NASA astrophysicist Zaven Arzoumanian teamed up to develop one. The contributions of citizen scientists have thus become even more valuable in identifying and tracking individual sharks.

Back on board the snorkel boat, I’m just starting to strip off my wetsuit when the skipper says manta rays might also be about. And then, “We’ve got a manta ray just surfaced, about 60 metres to starboard.” The calm voice of Steve, our dive master for the day, implies this is a common occurrence, but I’ve never seen a manta ray except on TV, so I’m hopping around the boat, giddy as a schoolgirl. “Where, where, where?” I yelp, scanning the water for any dark shape nearby. Then a pair of jet-black wingtips breaks the surface, and this majestic creature is gliding towards us with mouth agape as it trawls for plankton. Quick as a flash we’re back in the ocean, four manta rays swooping and wheeling about, three metres below.

I’m equally fascinated by a separate dive encounter I have here with an olive sea-snake – two metres long, coloured yellowish khaki with a black head. From the moment it appears, the snake follows our group of four scuba divers everywhere, swimming behind a pair of fins one moment, gliding between a pair of legs the next. Whenever we stop to examine a coral formation or peek under a ledge, the snake pauses and fossicks for a moment on the sea floor, but the second we move off it looks up as if to say “hey, where’s everybody going?” then resumes its pursuit. This strikes me as a feature of Ningaloo  world-renowned dive destination it may be, you still have to want to get here. The marine animals have remained curious, largely unthreatened by the presence of humans. Mark confirms my thoughts too about sharing the ocean with the tiger sharks, prolific at Ningaloo. “Thanks to large and dense populations of dugongs and turtles, and a healthy reef system, the tiger sharks here are kept fat and happy. They have little interest in humans.”

On the run home to Exmouth, I ask Neil, a fellow passenger who edits a dive magazine in the UK, about his first trip to Ningaloo. “There’s not a dive destination I know of where you could expect to see all the prize species that I’ve seen, and in just a couple of days – humpback whales, dolphins, dugongs, turtles, manta rays, sea-snakes, whale sharks, leopard sharks, grey nurse sharks, moray eels, tiger sharks, nudibranchs. Seeing even a couple of these would make for a brilliant dive trip almost anywhere else.”

Over 20,000 visitors come to Ningaloo each year, many of them to see the whale sharks. 300 to 500 whale sharks visit the area annually, mostly juvenile males. “An individual shark might encounter a handful of snorkellers in a season, so the impact on them is negligible. Some barely notice snorkellers; others seem to enjoy the attention. And tour operators here maintain the best-practice guidelines for whale shark tourism anywhere in the world,” Mark assures me. The strict guidelines require tours to maintain 3 metres distance from the sharks at all times, and 4 metres from their tails.

Whale sharks can live somewhere between 100 and 150 years. As Dr Mark Meekan has experienced over two decades, these animals are endlessly tolerant, majestic, and gentle, with humans. We will be a far better species ourselves if we can safeguard their survival into the future.