Log Transcript

This is Genevieve Johnson speaking to you from the central Indian Ocean.

The Odyssey crew have been researching sperm whales in the Indian Ocean for over six months. Having already found whales off the western and southern coastlines of Western Australia and the deep ocean trenches south of the Cocos (Keeling) Islands, we have just arrived inside the territorial waters of the Chagos Archipelago-a British owned territory in the center of the Indian Ocean, midway between the African continent and the great mass of islands that is Indonesia.

The Chagos Archipelago is a vast array of coral reefs sheltering five small coral atolls and numerous submerged atolls-all having been formed during a period of millions of years. The atoll rims are but the tips of spectacular underwater mountains, and it is just such bathymetric features that attract the animals on which sperm whales feed, which in turn attracts the sperm whales, which has in turn attracted the Odyssey crew to this remote part of the Indian Ocean.

After a three-week passage sailing west from the Cocos (Keeling) Islands, we are currently undertaking our first research leg around the southeastern reaches of the Chagos Archipelago, just below the southern most tip of the Chagos Trench - a 400 mile long, underwater canyon that ranges in depth from less than 1,000 meters below the surface to walls that plung very steeply to depths over 5,000 meters.

One of the most exhilarating parts of our research is searching for and finding whales in areas where no recent research has been conducted. As with many of the places the Odyssey has visited on the Voyage to date, we have no idea what we will find here.

Townsend's charts - Global maps showing the locations of sperm whale kills that were recorded in the log books of Yankee whalers between 1761 - 1920, are sometimes our only guide to finding whales in areas such as this. These charts show that sometime in the 18th and 19th centuries, Yankee whalers did indeed pass through the Chagos archipelago, and took a few sperm whales between the months of January and May. The trouble with this information is that Townsend's charts do not give any idea of effort-i.e. whether a great many or only a few ships passed through the area and secured the modest take that is indicated on the charts. After all, a given location may have produced one, or more (or many more) sperm whales. All that is shown is the position of the ship on the day that a sperm whale, or sperm whales, was (or were) killed. So we can interpret this in two ways: either the whalers were only in the area during the months of the year when whale kills occurred, or they were here in other months-perhaps even year round-but only found whales during the months indicated on the Charts.

Captain Rodrigo Olson inspects the main sail as the Odyssey circumnavigates the Chagos Archipelago.

Photo: Chris Johnson

This morning we detected two strong 'click trains' (evenly spaced echolocation clicks from sperm whales) on our acoustic array - two underwater microphones housed in an oil filled tube and towed behind Odyssey at a distance of 300 feet. We concluded from the intensity of the clicks, the distance between the whales we saw, and their sheer size, that these are probably mature male sperm whales. The clicks of females are not as loud as those of males, and females generally travel in family groups. Also, they don't grow bigger than about two-thirds of the length of a mature bull. Audio recording. - male

By the way, we are careful in determining the sex of the animals we see. There are several ways to achieve it: by entering the water and looking, or by genetic analysis, either of sloughed skin or the tiny skin samples we take from these animals with our biopsy darts.

So far, this time, we have spent four days with sperm whales. We moved on from the first two animals we were with yesterday, and today have encountered another individual also most likely an adult male. It is interesting that it is often the larger mature bulls that are the most timid, when boats approach them a few individuals sink below the surface, sometimes falling silent for two hours or more when the Odyssey sails or motors close to them. Perhaps these animals have used this trick before to evade detection, which could be the reason they are still alive today. Large males have always been the preferred target of commercial whalers-they yield far more oil than do the much smaller females.

The Odyssey will be circumnavigating the Chagos archipelago over the following month while we search vigorously for sperm whales. We're all excited at the prospect of what we may find in these waters, so stay tuned.

Links-

• To learn more about the Townend's Charts , click here.
• Sperm Whales echolocate to navigate and find prey. Find out about how they produce sound.
• Sperm Whales are the deepest of divers. Learn more about their dive cycle and diving physiology.

Log by Genevieve Johnson

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