Marine biologist and filmmaker Rick Rosenthal is the first to dive into and record the largest migration on Earth.

The "vertical migration" is the movement each evening of billions of ocean animals — teeming swarms of fish, squid, krill, jellyfish, tiny copepods and more — that swim upward more than half a kilometre from the deep to feed on plankton near the ocean surface in the darkness. Before sunrise, they swim back down to the relative safety of the depths.

Rosenthal's documentary Ocean Magic at Night airs on CBC-TV's The Nature of Things this evening. He spoke with about the challenges and rewards of filming the amazing phenomenon.

Cockatoo squid

This cockatoo squid is among the billions of ocean animals that rise more than half a kilometre from the deep to feed in the darkness on plankton near the ocean surface each night. (MBARI)

Why film the vertical migration?

The vertical migration is an important part of the food chain. Larger predator animals will eat at night when food like squid and lantern fish come to the surface where they are. That way, they don't have to dive so deep. 

We didn't really know very much about the vertical migration until the military started studying it in the mid-20th century. It's so thick that they would hide submarines under it. In some places, the vertical migration is so thick that it even changes the direction of ocean currents.

Why make a film now?

The technology is now there to allow us to film the migration. Digital cameras let you record at night with very little light. So you see incredible things with very little lighting. You don't want to use too many lights down there because you would be changing the behaviour of the animals you went to see.

Ocean Magic at Night – Intro1:27

What was the experience like?

There's no bottom, no reef and you're alone in thousands of metres of water. You're just a blob. You're almost mute to everything. You can't feel, taste, smell or hear. You have very limited vision and it's not that easy to move around. Really you're just a blob in the water.  It's feels like you're drifting in space looking for new life forms. You never know what's going to come out of the dark water.

Is it dangerous in the water at night?

It's nighttime on a boat when currents are stronger and you could easily drift away in just a few minutes.  I have a job to do, watching the wildlife through my lens, so I can't be watching for the boat all the time.  As a safety device, I had a beacon that would send an emergency signal out to the nearest boat if I got lost, but we didn't have to use it.

I'm not an adrenaline junkie — that's not why I do this. I'm driven by catching something new on film, giving people a look at how astounding the ocean is.

Rick Rosenthal and Captain Bishop

Cameraman and marine biologist Rick Rosenthal, seen here with Captain Bishop, is the first person to captured the vertical migration on film. (CBC)

How would you see large fish at night?

We didn't see many, but of course they were there. We could see them on sonar. They knew that the boat was there and that I was in the water and they stayed away.  Also, I think that the large fish and mammals were dispersed over a big area because the migration is so large.

Where did you travel for Ocean Magic at Night?

We needed warm water that you could hang out in for a few hours and really clear visibility to we could capture the migration at a distance. We needed to be able to just turn off the lights and hang there.  Mostly we worked in Hawaii, Costa Rica and Panama.

A lot of the animal life just doesn't come up into the dive zone, which is about 30 metres deep. Research has shown us that the animals stay where the brightness is about one per cent of full daylight. There was a lot of wildlife below us that we couldn't see on camera.

Ocean Magic at Night – Hiding in the Dark1:56

What's next?

I'm working with Chris Carter (creator of the X-Files) on a film about El Nino.  The ocean creatures have been telling us that one is coming. The ocean water near San Diego is getting so warm and we are seeing creatures here that we've never seen before.  El Nino is a complicated event, it means flooding for some people, drought for others. It's kind of a boom or bust event.  So we're going to tell this story in a very non-traditional way — like solving a mystery.

How did you get interested in the deep water filmmaking?

I grew up in San Diego where there were lots of marine biologists and places to dive. I became a marine biologist and started taking pictures to go with my papers. But I realized that nobody reads scientific papers, so I turned to filmmaking as a way to communicate with more people.

Series like Blue Ocean and Planet Earth were megahits.  Even if one per cent of the people who see the film get the message, that's huge.

Barrel-eye fish

Today's digital cameras let you see and record incredible things, such as this barrel-eye fish, with very little lighting says filmmaker Rick Rosenthal. (MBARI)

What's your biggest message for people?

There are still magical worlds on our planet — and new species are being discovered all the time. We don't have to go into space, it's happening here 24/7. We now have the tools to explore them and we need to observe and record these places before we lose them forever.