TAKE a strong, silent hero. Throw in a fast-moving chase, a bit of gratuitous
violence and a steamy sex scene and you have the makings of a box-office hit.
The plot might be a bit vague and the hero doesn’t say much—but the
audience hangs on every grunt. The star of this particular movie is no Clint
Eastwood or Sylvester Stallone. Our hero is bald, paunchy and popeyed. He’s a
Hawaiian monk seal, and not only is he the film’s star, he’s the cameraman and
the director too.
The Secret Life of a Monk Seal is the result of a simple idea, a bit
of off-the-shelf technology and years of tenacity. The idea is the brainchild of
Greg Marshall, a marine biologist who works in the Natural History Unit at
National Geographic Television in Washington DC. What better way, he thought, to
get the inside story on a marine creature’s life than to fit a movie camera to
its back and let the film roll?
A decade ago, Marshall created the prototype “Crittercam” from an ordinary
camcorder stripped down to its bare essentials and rehoused in a metal tube
designed to withstand both high pressure and the sort of battering a powerful
animal is likely to give it. That was the easy bit. Persuading someone to fund
the research, finding field biologists willing to try Crittercam on “their”
animals, and tailoring the device to suit different species were more
difficult.
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“It took a long time to convince people that it wouldn’t harm the animals,”
says Marshall. Now, though, marine researchers are queuing up at his door. Even
those who thought Crittercam was just some fancy film-maker’s toy now admit that
these fly-on-the-wall documentaries are providing remarkable insights into the
behaviour of animals that are impossible to study any other way. “Every species
we work on reveals something entirely new that we haven’t anticipated,” says
John Francis, who gave up his studies of fur seals to make films. “Using this
tool almost guarantees you will make a new discovery.”
From turtles to sharks, seals and sperm whales, Marshall and his team have
spied on all sorts of marine creatures. But it is the films of
pinnipeds—seals and sea lions—that have transformed Crittercam from
a provider of tantalising glimpses of an animal’s most intimate secrets into a
respectable scientific instrument. Pinnipeds have one big advantage when it
comes to attaching a camera. Unlike whales or sharks, seals and sea lions haul
out on the shore, and after a trip to sea they tend to return to the same
place—which increases the chances of retrieving the film.
Watching a film shot by a seal can be a disconcerting experience. One minute
you’re swimming along behind the seal’s head. The next, the world turns upside
down as the seal twists and turns through the water. Suddenly, the seafloor is
above you and the sunlight is shining up from below. A headless seal swims into
view, which is very peculiar until you realise the seal has simply stuck its
head above the surface into the world you cannot see. After a while, you begin
to get the hang of being a seal. And that’s the point. “I’d sat on the coast
watching seals for thousands of hours,” says Francis. “But every time they went
into the water it was like a black hole. Then within a few minutes you could
see—you could get inside the skin of a seal.”
This new-found ability to follow animals into the deep has revealed
intriguing aspects of the lives of three species of pinniped, including entirely
new types of feeding and mating behaviour. Perhaps more important, it highlights
the dangers of drawing conclusions based on what animals seem to be doing on
land or at the surface. In the case of the Hawaiian monk seal, its very survival
could depend on knowing what it does when it’s out of sight.
The number of Hawaiian monk seals has plummeted by 60 per cent over the past
40 years and now stands at around 1200. On the western Hawaiian islands of the
French Frigate Shoals, where a third of the population lives, the numbers are
still falling. Some animals are victims of unaccountably aggressive males who
spend hours harassing youngsters and females. Crittercam filmed one big male
pestering a youngster for three hours, and another that stalked a female for
three days. But many young animals seem to be suffering from malnutrition. It is
this that really concerns biologists at the National Marine Fisheries Service in
Honolulu, which is responsible for protecting the seals. “They seemed to be
starving, so we wanted some insight to their foraging strategy,” says Frank
Parrish, a fisheries biologist with the NMFS.
Before Crittercam, the researchers could tell where the seals went and how
deep they dived from satellite telemetry and depth-of-dive recorders. “But we
had no idea what they were doing underwater or which habitats were important for
foraging seals,” says Parrish. Dive records show that the seals spend most of
their time in the shallow waters of the atolls. “They rely on the shallows for
protection from the ocean,” says Parrish. “We assumed that the shallows provided
the staple of their diet.”
Film shot from the back of male monk seals showed how unreliable intuition
is. Far from feeding in the shallow waters in and around the reefs, the monk
seals headed out to sea, blithely ignoring schools of reef fish. Only when they
reached water between 60 and 100 metres deep did they start to hunt. At this
depth there is a boundary zone where the coral rubble at the bottom of the reef
slope meets open sand. On the rubbly side, the seals flip over rocks hunting for
octopus, crabs and sheltering reef fish. On the sandy side, they drill into the
sediment with their noses and dig with their flippers, flushing out fish such as
conger eels and flounder. These deeper waters may well be a “critical habitat”
for monk seals, but unlike the waters around the atolls, this zone has no
protected status.
In the cold Atlantic Ocean off Nova Scotia, Daryl Boness, head of research at
the Smithsonian Institution’s National Zoo in Washington DC, hopes Crittercam
will solve a rather different mystery. He has spent almost 20 years observing
the harbour seals of Sable Island. “A few years ago, it struck me that all our
ideas about mating are based on how the animals behave on land.” When seals mate
on dry land, a few dominant males tend to command a harem of females or a
territory, which they defend aggressively. There is little doubt about who is
mating with whom. Harbour seals, however, mate at sea, so males must have some
strategy for intercepting or attracting females when they enter the water.
To build up a detailed picture of the behaviour of individual seals, Boness
programmed Crittercam to film for short intervals throughout the day on
consecutive days (see “Lights, camera, action!). He also tracked each seal by
radiotelemetry. “You get a picture of the time spent foraging, resting or
displaying,” he says. And as the season progresses, you can see changes in their
activities.
After four breeding seasons, Boness had enough data for statistical analysis,
and a good idea of what the males were doing. During the crucial part of the
breeding season, males spend less time foraging offshore and move closer to the
beach, where they patrol small areas within a kilometre of the shore. During
this period the film showed them doing things no one had ever seen before. The
males swim close to the seabed, making a low, rumbling noise that sets their
necks quivering. “It’s an intense broad-frequency sound that builds up to a
crescendo and ends in a crashing sound,” says Boness.
Males carry on swimming and rumbling for long periods. But every fourth or
fifth quiver, they rise to the surface, blowing out a stream of bubbles as they
go, before dropping down to the bottom and starting the neck quiver again. When
it first showed up on film, the experts argued about what the animal was doing.
“By the second season there was no doubt,” says Boness. “It’s clearly a form of
reproductive display.”
All the evidence suggests that males must compete for the females’ attention,
although Boness doesn’t know yet whether these displays are aimed at attracting
a mate or warning off other males. The fact that when females venture into the
water they don’t seem to mate with the nearest male suggests that unlike seals
in a harem, they have some choice about their partner. Just what makes one male
more attractive than another remains to be answered. “We don’t have enough data
yet to analyse the success of different tactics,” says Boness.
Across the ocean in the cold southern Pacific, Crittercam has another mystery
to solve: why fishing nets are so attractive to New Zealand sea lions. These are
the world’s rarest sea lions, with around 12 000 animals, mainly living around
the remote Auckland Islands, 300 kilometres south of New Zealand. In the past
few years, New Zealand’s Department of Conservation has grown increasingly
worried about the number of sea lions drowning in the trawls of the squid boats
that fish around the islands.
In 1994, Nick Gales, a vet and marine mammal biologist, was sent to the
islands to investigate. That meant, among other things, finding out where the
sea lions feed and what they eat. To begin with, he collected data from time and
depth recorders, which measured the animals’ depth every few seconds. Satellite
transmitters attached to the sea lions told him where they were.
These instruments showed that there were several distinct types of dive with
characteristic profiles—sharp V-shaped dives in mid-water, for instance,
or flat-bottomed dives with a long spell on the seabed. “The results were
exciting,” says Gales. These sea lions dived deeper—down to 570
metres—and stayed down longer—up to 11 minutes—than any other
sea lion or fur seal. “Naturally we wondered why they need to dive so deep and
wanted to know just what they do when they are down there.”
Crittercam has begun to answer some of his questions. Early last year,
several cameras were fitted to female sea lions. “The New Zealand sea lion must
be one of the worst candidates for this work as it dives to enormous dark depths
and grubs around on the bottom,” says Gales. It also pokes about in submerged
caves, a habit that made for anxious viewing each time a wall of rock filled the
TV screen.
To try to throw a little more light on what the animals are doing at depth,
the instruments were equipped with headlights, a ring of red LEDs that
illuminate the area two or three metres in front of the seal’s nose. Red light
doesn’t seem to disturb either the seal or its prey. “At last we could visualise
the behaviour during those long, flat bottom parts of the dives,” says Gales. “I
was able to see the sea lions moving fast along the ocean bed, sweeping their
heads left and right looking for prey. I could see them wedged into deep-sea
caves trying to extricate prey from crevices.”
With the next generation of Crittercams Gales hopes to identify the sea
lions’ prey and study their hunting techniques—and discover how they end
up in squid nets. The opening of a squid trawl being dragged through the water
is about the size of a football pitch. “We don’t know if sea lions get caught by
chance as they go about their normal foraging or whether they actually pursue
squid into the net and become trapped,” says Gales. The film shows that they do
eat squid. Gales hopes the sequel will provide direct evidence of their
interaction with nets.
As far as seals and sea lions go, the on-board camera has been a huge
success. Other species are proving more reluctant movie stars. Trying to attach
a camera to a great whale poses a different type of challenge—and then
there is the problem of retrieving the film. But Marshall and his team are
working on it. “If a picture’s worth a thousand words,” says Francis, “then a
moving picture is worth a thousand pictures.”
CRITTERCAM is a stripped down camcorder repackaged to make it as small as
possible. A few adjustments to the optics increase its field of view. “It was
with great trepidation that I ripped apart the first camera,” says Marshall. The
main concern for him and the biologists he works with is that the camera
shouldn’t be a burden to the animal. “Any drag would have a cost for the
animal,” says Marshall. Nor should it disrupt the animal’s normal
behaviour—or scientists could get some wrong impressions about their
species.
So the camera has to be light and streamlined—and it has to withstand
high pressure when the animals plunge into deep water. The best shape is a
simple cylinder, with a domed nose to reduce drag. For most animals, an
aluminium casing is strong enough—as long as they don’t go deeper than 600
metres. But for deep-diving species, only titanium will withstand the immense
pressure. Most models are 10 centimetres across and between 20 and 30
centimetres long. “It surprises me that we don’t see any effects on the animals.
They just go out and do what they are supposed to do,” says Marshall.
Besides the camera and three hours of film, there is a microphone to record
any sounds the animal makes and instruments that continuously log the animal’s
depth and location, the light level and the water temperature. In the early
days, the biologists had little control over the filming once they let the
animal go: the camera just kept rolling until the film ran out. Today, they can
decide exactly when and for how long they want to film, programming their
shooting schedule remotely from a laptop.
Crittercam is improving all the time. In the National Geographic lab in
Washington DC, the team is building new packages with digital video cameras that
halve the volume of the gear. They are also experimenting with image
intensifiers—based on recently declassified military
“nightscopes”—for use on deep diving animals such as sperm whales. “When
they disappear into the dark they are still doing interesting things. We want to
see what they are,” says Marshall.