Specialised equipment, elusive subjects, and the courage to brave the ocean – underwater photography presents unique challenges and opportunities. The Ocean Photography Awards exist to recognise the brightest and best aquatic images, in six categories ranging from ‘Conservation’ to ‘Adventure’.

Canadian photographer Nadia Aly was named Ocean Photographer of the Year, thanks to a wide portfolio of entries documenting everything from hairy frogfish to mantis shrimp. Hers were among 3,000 entries to come in from all over the world – and these are our favourite shots…

(Nadia Aly/Ocean Photography Awards/PA)

The overall winning image, this snap by Nadia Aly shows a mass of Mobula rays off the coast of Baja California, Mexico. "Mobula rays are incredibly sensitive to movement and sound," she says, "so I took this photo while freediving. We found them mid-morning and stayed for four hours."

(Jason Gulley/Ocean Photography Awards/PA)

Photographer Jason Gulley captured this remarkably colourful image of a cave diver entering Little River Spring in Mexico during a flood, earning a highly commended in the exploration category.

(Fred Buyle/Ocean Photography Awards/PA)

This free diver may look like he’s swimming through the cavern, but the ‘ceiling’ is actually the underside of a crashing wave. Snapped off Rurutu Island, French Polynesia, Fred Buyle had gone down looking for humpback whales, but took this highly commended image instead.

(Maxwell Hohn/Ocean Photography Awards/PA)

Looking more like a large pond than anything oceanic, these Western toad tadpoles were actually spotted off the coast of Vancouver Island, Canada, by photographer Maxwell Hohn. He had plenty of time to get the pic, as he’s been snapping and studying the species for four years.

(Henley Spiers/Ocean Photography Awards/PA)

Submitted by award-winning photographer Henley Spiers as part of his second place-finishing Collective Portfolio, this image shows a sedate Olive Ridley Turtle resting on a sea bed just off the coast of Mexico.

(Cruz Erdmann/Ocean Photography Awards/PA)

The winning image from the Young Photographer of the Year category, this shot by Cruz Erdmann portraits a Maldivian anemone fish nestling in the fronds of a so-called Magnificent Anemone. "This photo was taken in time with the surge of waves overhead," he says, "just as the tentacles revealed the full body of the fish"

(Ben Cranke/Ocean Photography Awards/PA)

An ethereal shot of penguins battling strong winds and snow in St. Andrew’s Bay, on the Antarctic island of South Georgia, this photo ranked first in the Exploration category, and was taken by Ben Cranke. He spent 50 hours on location, and caught this shot on his final day.

(Nadia Aly/Ocean Photography Awards/PA)

Part of Nadia Aly‘s winning portfolio, this photo shows male giant cuttlefish surrounding a female near Whyalla in South Australia.

(Sean Scott/Ocean Photography Awards/PA)

Two sharks frolic in the midst of a breaking wave at Quobba Station, Western Australia, in this image by Sean Scott. One of a handful of entries to be taken from the shoreline, it finished runner-up in the Adventure category.

(Florian Ledoux/Ocean Photography Awards/PA)

The third place finisher in the Exploration category, this aerial snap by Florian Ledoux shows crabeater seals lounging on two slabs of floating Antarctic ice. After days crawling through the sea ice, Ledoux finally got a chance to photograph the seals resting right after a meal.

(Nadia Aly/Ocean Photography Awards/PA)

An immaculately framed image, Nadia Aly found this jellyfish backlit by streaming sunlight, like a see-through solar eclipse. It was taken in the appropriately named Jellyfish Lake, on the South Pacific island of Palau.

(Henley Spiers/Ocean Photography Awards/PA)

Another image from Henley Spiers‘ portfolio, this elegant black-and-white composition presents a school of spotted eagle rays gliding gracefully together near the Maldives.

(Grant Thomas/Ocean Photography Awards/PA)

"In creating this picture, timing was everything," says Grant Thomas of this highly commended image capturing paddle boarders above a reef at sunset near the Tongan islands of Vava’u. "I had to shoot exactly at low tide to be close enough to the reef, while capturing the sun as it hit the horizon."

(Tanner Mansell/Ocean Photography Awards/PA)

A nominee for the Community Choice Award, this portrait of predator and prey was captured by Tanner Mansell off the coast of Florida. "When bull sharks attack they extend their jaws," he says, "and it was exciting to try and get that moment on camera."

(Nadia Aly/Ocean Photography Awards/PA)

Another effort from the portfolio of Nadia Aly, this seahorse posed perfectly for a picture off the coast of Komodo, Indonesia.