But time spent underwater is well spent when it reveals previously unknown secrets about our world.
“The Holy Grail is to film something that no one has seen before”, says Doug.
“For example, that trevally sequence in programme one [of Blue Planet II], with the big fish leaping out of the water to catch birds in mid-air.”
But even with all his experience, there remains one animal that Doug has yet to successfully film and he’ll have to go back to the Arctic to find it.
“There’s a small whale up there called the narwhal,” he says. “And the great thing about it is that the male’s got a single ivory tusk growing out of [its] upper jaw.
“They’re extremely wary, but I am going to go up there and try again, and if I get it I will drown a happy man.”