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LatestPhoto
The large nose of the sperm whale obscures its ability to see. To solve this problem, it must roll on it's side or lift the nose vertically to achieve forward, binocular vision.
Photo: Chris Johnson

February 19, 2003
A Busy Day
  Real Audio Report
  28k


Log Transcript

Sailing south along the north-western coast of the Maldives archipelago, it's good to be with whales again.

Yesterday morning Risso's and Striped dolphins paid the Odyssey a visit. The afternoon saw us sailing parallel to a small group of beaked whales. Sightings of beaked whales at sea are extremely rare, when they are seen, the exact species is difficult, if not impossible to identify. These whales usually spend exceptionally short periods of time at the surface and are notoriously shy of boats. Fortunately we managed to take several photographs of the animals, which remained at the surface for around four to five minutes. We were also able to take shots of the heads as they broke the surface - head shots are the key to identification in beaked whales. Characteristics such as melon size and shape, beak length and the presence or absence and position of teeth, vary dramatically between species. We will develop the film when we reach port, hopefully these images will enable us to identify the exact species. So stay tuned.

In the early hours of this morning, we detected the slow rhythmic clicks of a single sperm whale through the acoustic array - the underwater microphone we tow behind the Odyssey. We turned north and followed the whale until dawn, the early sunlight affording the crew an opportunity to collect a small tissue sample.

It appeared as though this whale was a single male, perhaps in search of a group of females with whom he could mate. As we sailed in his direction in preparation to collect data, he also turned and headed directly toward us. The sight of a sperm whale facing you head on sends shivers of excitement up the spine. With the engine turned off, the only sound we could hear was the waves lapping gently against the hull. The tranquillity was suddenly shattered by an almighty 'WHOOSH', - the massive exhalation blow of a whale is strikingly loud.

LatestPhoto
Peter examines a dead Green turtle hauled aboard the Odyssey.
Photo: Chris Johnson

We watched in awe as the huge animal closed the distance between us. The nose of a male sperm whale can weigh up to ten tons, making up approximately one third of the entire body length and 1/5 of the weight. The relatively small eyes are situated on the most lateral part of the body, far back on the head, about one quarter of the body length back from the tip of the nose. Understandably, a nose of such epic proportions - the largest in the animal kingdom, can obscure the whales' ability to see what is directly ahead of it. Sperm whales have a blind spot from approximately zero to fifteen degrees both in front of the nose and behind the tail. When swimming parallel to the surface, the sperm whale only has binocular vision directly below its body. Binocular vision is when both eyes can see the object of interest at the same time. This in turn provides more detail and allows for vastly improved range estimation. Most animals that rely on vision for foraging and orientation have their eyes placed next to each other, pointing forward. This is also the case in humans where almost all objects are in the visual field of both eyes. In animals where vision plays a minor role, such as in the sperm whale, which uses echolocation as it's primary sensory cue for orientation and prey finding, the eyes are placed on the lateral side of the animal to increase the field of vision. The price to pay for this is that the visual field covered by both eyes is very small. In order to solve this problem, a sperm whale must roll on its side or lift its nose vertically, to achieve forward binocular vision. This whale appeared to do just that. The crew gasped as the massive scratched and scarred nose, rose majestically above the surface - the whale was looking at us! It appeared to hang in mid air momentarily, then without a sound, or even a splash, the animal gently submerged. It amazes me how much difficulty a human diver has entering the water without making a splash, yet here is an animal whose ten ton nose makes barely a ripple at the surface as it disappears.

After collecting data, we left this whale in search of the next. Early in the afternoon, Pernille - the Odyssey Science Intern, radioed to the helm from the observation platform that she could see what looked like a turtle floating at the surface. We motored toward it and quickly realized that the bloated, lifeless body belonged to a Green turtle.

We hauled it onboard to look for any signs of injury or entanglement that may have caused its death, but none was apparent. What was shockingly apparent was the putrid small of rotting flesh.

LatestPhoto
Cynde, John and Hussein - our observer from the Maldive Marine Research Center - work together to collect and compare data on whales.
Photo: Chris Johnson

With no obvious sign of injury, and the fact that the turtle was not particularly old - we could deduce this from the size of its carapace or shell, we were curious as to what may have been the cause of death. There is only one way to find out for sure, and that is to perform a necropsy - we could have cut it open to take a look. While debating whether or not to perform the procedure on the decomposing turtle, we detected another sperm whale. All hands were needed on deck to collect data, there was nowhere to store the rotting turtle, so we took some photographs and the decision was made to return the carcass to the sea. As sad as it is to see an animal in this condition, the turtles misfortune translates into a meal for a hungry predator - where there is death, there is also life.

This is Genevieve Johnson speaking to you from the Odyssey.

Links:

  • What did the crew of the Odyssey report on one year ago in Australia? Two years ago in Papua New Guinea?

    Written by Genevieve Johnson & Peter Teglberg Madsen

 
 
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