By Tom Gillespie @TomGillespie1
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The enormous creatures, pictured here in Crystal River and Homasassa Springs, are personable animals who are renowned for their willingness to approach humans in the wild.
In the winter months the gentle giants journey to warm waters from the Gulf of Mexico, where freezing temperatures can be potentially fatal.
Underwater photographer Nick Robertson-Brown said: “They are amazing to snorkel with, and there are strict rules about how to behave when in the water with them.
"They are really curious - they make the approach and can get quite possessive if they chose you, shepherding any others that come for attention away.
“You are only allowed to touch them with one hand at a time, and there are 'no entry' zones for humans, so the manatees can go and sleep or seek refuge.
“They are very big animals, and so getting up close is a real treat.
Nick and his wife Caroline captured the images on trips in January 2011 and February 2012, but are releasing the images now to highlight efforts to reduce the number of manatees who die in freezing temperatures.
Nick added: "It had been on our wish-list for many years and they are just so wonderful to photograph.
"They move slowly and approach you head-on so they are easy and a pleasure to photograph.
"I had one hug me with its huge flippers, it was an absolutely wonderful experience.
"They are just so endearing and love scratching their backs on our kayaks."
Despite their size the animals have relatively little body fat, and cannot survive temperatures below 68F for long periods of time.
Nick continued: "Manatees are particularly susceptible to the cold, and many die when temperatures drop.
"The numbers that are rescued each year depends on how cold it gets and also if poisonous red algae blooms.
"But sadly there are always boat strikes and net-trapped victims.
"In 2014, 67 were rescued from the water and only 27 survived to be released back into the wild. In 2013, 88 were rescued and 57 of these survived and now live in the wild."
Nick, 62, and Caroline, 42, met as biology students at Manchester University, and live together in Sale, Greater Manchester.