Anatomy of a shoot: Lemon sharks in feeding frenzy
BBC Two's Great Barrier Reef team set out to film the incredible action of lemon sharks leaping out of the water while catching fish. Series producer James Brickell reveals how they shot the sequence, what they actually witnessed and how the footage they captured may have revealed new shark hunting behaviour.Research
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Sharks are not renowned for their intelligence. Senses yes, intelligence no. The thought that they may use another animal to help them hunt seems somewhat unlikely.
There are examples of them hunting in numbers, or several sharks attacking the same prey at the same time, even hunting alongside other animals such as dolphin, tuna or sea birds; but is this co-operation or team work?
The animal world constantly surprises me and whenever I have spent any length of time watching some sort of behaviour it is not unusual to see something that I cannot find mention of in any book or scientific paper.
So it was the case with the lemon shark sequence for Great Barrier Reef.
My colleague, Bess Manley, had seen a story in the local Port Douglas newspaper showing lemon sharks hunting in very shallow water on an island cay called the Low Isle.
The picture in the article showed a lemon shark, thought of as a relatively sluggish shark, fully breaching the water to catch fish - it looked more like a great white than a lemon shark.
I wanted to capture these leaping lemon sharks as a nice, action-packed sequence in the part of the film talking about the influence of the tides.
The behaviour seemed to be happening fairly regularly so Bess and I headed over there with cameramen Mark MacEwen and Cameron McGrath.Planning the shoot
We required a ridiculous amount of equipment.
As well as the usual crippling load of cameras (both topside and underwater), valuable lenses, cumbersome tripods, heavy batteries and boxes of provisions to sustain us on the island; we packed a "Jimmy jib".
This is a device that looks a little like a crane.
The idea is that you attach a camera to one end of its ten metre arm and some weights to the other. Then, using a complex arrangement of motors, cables and controls you can point, zoom and focus the camera in all directions whilst swinging the arm around.
Theoretically, it is portable... But that is compared to say, an actual crane.
In fact, normally, the cumbersome device would be utterly impractical for filming wildlife behaviour. But I just had a hint that we might get an opportunity to film the sharks hunting with it.On location
The main island on the Low Isle is small. A narrow sandy beach surrounds it and you can walk around its forest centre in about ten minutes. When we arrived there was very little sign of the sharks.
The island's only residents, a couple who look after the permanent research station, told us the lemon sharks would be back, so we waited.
Waiting is part of the deal with filming animals.
By the end of our second day things started to improve; there were a few large schools of baitfish swirling in the shallow water just off the beach.
Then a few fins appeared; the sharks had returned.
At first, though, there were no signs of feeding. The sharks were just swimming lazily through the fish time and time again; they might as well have been best buddies.
However, by cruising in slow, predictable patterns along the shallows, it made it relatively simple for me to wade into the water as the sharks passed and place some of our small underwater cameras on the sand, so we could snoop on what was happening.
LEMON SHARK FACTS
- Lemon sharks get their name from their camouflaged yellow-brown skin that helps them blend into the sandy floor
- Lemon sharks usually grow to a length of around 2.5 to 3m
- Female lemon sharks give birth once a year to live young, known as pups, in litters ranging from four to 17 baby sharks
- Lemon sharks don't reach maturity until they are around 12 to 15 years of age
- They can tolerate a high range of water salinity and have even been documented swimming in freshwater rivers for short periods
Slowly, hour-by-hour, the behaviour of the sharks started changing: we started seeing them snapping at the baitfish occasionally. Not exactly the full-on hunting we were after but it was a promising start.
It was not until we viewed the footage from our underwater mini-cameras that we started seeing something unusual.
As well as the sharks, there were other predators showing an interest in the school that we could not see from the surface.
Small trevally, young barracuda and needlefish all appeared in the footage darting into the school, and with each hi-speed attack they made, the bait fish were scattering.
It was the behaviour of the other fish that appeared to be triggering the sharks to feed.
When each small, fast predator charged through the fish it was creating a tiny window of opportunity when the schooling behaviour was broken up.
It barely lasted a second but it was long enough to give the larger slower sharks an opportunity to bring their own weapons to bare.
These "sicklefin lemon-sharks" are not lightening quick swimmers, so by schooling tightly in a co-ordinated mass, the small bait fish have an effective defence against them.
The sharks can however snap their jaws very quickly in their immediate vicinity. So if the bait fish school is broken up, even for a second, and the sharks are in the right spot and they react fast enough, they have a chance to grab a fish.
As the days passed the sharks' hunting behaviour became more aggressive and more predictable. We decided to set up the jib arm and attempt to get our large camera above the action to give us a bird's-eye view of what was going on.
It was a risk. It was heavy, even for four people to carry, and we had no idea how any of the fish would react to a giant shadow above them.
After hours of carrying the kit up and down the beach and laboriously repositioning it we were able to swing the arms out over the action.
Now, from our make-shift hide on the beach, we could see straight down through the water's surface, using polarising filters to cut out any glare from the sun.
It was almost like the water was not there and we could see exactly what was going on. The more we filmed the more it confirmed our idea.Results from filming
The tactic was obvious and effective; the shark attacks occurred a split second after those of the smaller trevally, barracuda and needlefish.
But were these deliberate on the part of the sharks? Had they just been waiting for the other fish to make their move? Or was it all one big happy accident, brought about by lots of predators taking the same opportunity?
It is very difficult to prove one way or the other.
Science demands hard data to prove such things, and a few minutes of footage is really just the start of the story.
So until someone gets an opportunity to study it for any length of time we will not know for sure but it has certainly convinced me that the lemon sharks are more intelligent than we give them credit for.
Great Barrier Reef continues on BBC Two at 20:00 on Sunday 8 January