Exploring the secrets of Blue Planet II

Exploring the deep ocean and seeing rare and fantastic sights may seem like a dream job, yet it can come with a bittersweet tinge.

Orla Doherty is one of the producers of the BBC series Blue Planet II and she oversaw just some of the 6,000 hours spent underwater it took to create the seven-part nature documentary series.

As documentaries go, Blue Planet II has the potential to be one of the most important created, as it documents all manner of life in an ever increasingly fragile ocean.

The series, narrated by the nature documentary legend Sir David Attenborough is a sequel to the multi-award winning Blue Planet, first broadcast in 2001.

In the time since, the state of the oceans has worsened. Global warming has affected the temperature of the seas, in-turn affecting the marine ecology. Every year, an estimated eight million tons of plastic waste ends up in the ocean. It can look like a very bleak outlook for the ocean. Yet, Doherty says there is hope.

This new series took four years to produce, with 125 expeditions taking in 39 countries across all continents.

The efforts have paid off somewhat with the first episode becoming the UK's most watched programme of 2017 with an audience of 14.1 million.

In an interview with The New Paper, Doherty described her experience making the series.

TNP: Being able to explore the oceans with cutting-edge technology sounds like a dream job.

OD: There is an awful lot of time spent at your desk devising the stories, researching them and then figuring out how you're going to film them.

For some of the expeditions I worked on for The Deep episode took two years of prepping and planning, getting permits, organising logistics.

But then there's the other side when you get to go out into the field.

Our teams worked in all types of water whether it's shallow or deep.

For me, it was particularly exciting because a lot of my time was spent in submarines or using remote vehicles to explore the deep ocean.

TNP: This feels like an important series. While the footage is awe-inspiring, there's also a tinge of heartbreak knowing that for some species, this could be a "last chance to see"...

OD: If you spend time in the ocean, you're always going to be amazed and wonderstruck by what you find.

It's the largest habitat on Earth, covering 70 per cent of the planet and there's a lot of life in there.

And yes, the ocean is in a very fragile state right now.

Our hope is that we shine a light on these incredible animals that live in it, how they work and what they need to live in it.

We have great hopes that people will connect with the ocean in a way that maybe they haven't before.

TNP: Are there any sights that overwhelmed you?

OD: Oh yes. We caught this one-time event of basketball-sized bubbles of methane erupting from the deep sea floor off Mexico. It was like being on a different planet.

Our jaws were on the floor. It had never been seen before. Even the scientist who led us to that site had not seen it.

Because it's the deep ocean, it could be happening a lot more often and we just don't know because we can't live down there - unfortunately.

If somebody could work out how to keep us down there for months, I would stay there.

TNP: Astronauts have said that they have trouble readjusting to life on Earth after experiencing life in orbit. Seeing these rare underwater sights, do you have trouble adapting back to life on dry land?

OD: Yes. I never want to leave.

When we go down in the submarines, we stay down for as long as possible - maybe 10 hours at a time - but it goes by in a flash.

So when the sub-pilot says the batteries are running low or that life support says we need to return to the surface, whatever the reason, I hate that moment.

I just don't want to go back up.

TNP: Has your experience underwater affected you in other ways? Do you avoid eating fish?

OD: I was always quite conservative about eating fish but I don't eat shrimp anymore.

That comes directly after a dive in the Gulf Of Mexico at around 700 metres deep.

It should have been a dive at a beautiful deep sea coral reef but what we found was a rubble field.

A trawler had been through dragging weighted nets on the seabed. It was like being on a shallow reef that had been dynamited, which is something I've seen during my studies.

It was razed to the ground, all done by weighted nets looking for shrimp. Now I avoid seafood altogether.

TNP: The series manages to capture many rare underwater sights. Did anything prove too difficult to capture?

OD: Around the end of 2014, we went to the coral sea off Australia to capture the phenomena of lantern fish spawning.

They are deep sea fish, one of the most abundant species on the planet, though we rarely hear of them because they live so far down.

But they are meant to come up for this mass spawning event that is determined by the lunar cycle.

We went out to capture it but because of El Nino (A warming of ocean and atmosphere in the east-central Equatorial Pacific) which was just starting at that time, the whole ocean cycle was off.

The tuna were doing different things to what they normally do. And crucially, the lantern fish were not there.

It was a real wake up call as it was the first shoot of the series. It was a failure but it reminded us just how unpredictable the ocean can be.

TNP: Is there one piece of technology that has proved invaluable for this series?

OD: The rebreather (a breathing apparatus that both absorbs the carbon dioxide of exhaled breath and recycles unused oxygen).

Using it means that instead of emitting these loud bubbles every time you breathe out, disturbing all animal life around you and scaring fish away, you become part of the landscape.

Also, your time underwater is increased so we had divers staying underwater for four hours at a time.

That helped us get really close to animals without disturbing them. Rebreathers were around at the time of the first Blue Planet series, but they were very new tech at the time. The technology has really advanced since then.

TNP: How worried are you about the oceans?

OD: Actively concerned. The oceans are changing more than they ever have done before and that's down to us.

But I'm also hopeful. In the last episode - Our Blue Planet - we have shined a light on the big issues and some of the ways we are affecting the oceans.

But we also highlight the individuals and groups who are really trying to make a change either for a particular animal or an area of ocean.

One example is a guy in the Caribbean who realised the leatherback turtles who went to his beach were seriously under threat.

He managed to turn his whole community around and instead of harvesting the leatherbacks for their meat, he managed to gather a band of leatherback "warriors".

They do everything in their power to change the fortunes for their leatherbacks. They protect the beach, relocate the eggs and educate the kids there.

When you come across stories like that, you can't be anything but hopeful.

There's no one-size-fits-all solution for what we've done to the ocean but with intelligent thinking and action, there is so much that already has been achieved.

And maybe through Blue Planet II people will be inspired to think about what can be done in their patch of ocean.

Blue Planet II is on BBC Earth (Starhub Channel 407) and on BBC Player