Log Transcript

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

The other day we came across an enormous group of dolphins. As they approached the Odyssey, their distinctive markings made it easy for us to identify them as striped dolphins. This was no small pod, these dolphins numbered close to 150 animals, although they have been known to run in groups numbering in the thousands. This is only our second sighting in two years, the first being in the waters surrounding the Galapagos Islands.

These are an exquisite species, one of the most strikingly beautiful dolphins you are ever likely to encounter. Striped dolphins are instantly recognizable by their stunning color pattern. Their delicate black beak sends back a distinctive stripe that encircles the eye, then widens and runs almost the entire length of the body. A second thin stripe tapering off behind the eye to the flipper gives this dolphin a delicate hand painted appearance.

Striped Dolphins are extremely acrobatic, capable of leaping more than 20 feet out of the water.

Photo: Genevieve Johnson

The dolphins remained with the Odyssey for over half an hour. Many animals 'rode the bow' then appeared to move off as though allowing other individuals to take their turn, this included at least two mother/calf pairs. Interestingly this species is renowned for being shy of boats, but we were yet to make any such observations. The dolphins were spread out on either side of Odyssey demonstrating plenty of surface activity, their amazing acrobatics included backward somersaults and leaps as high as 20 feet.

Without warning something appeared to startle the school, perhaps a shark, and they immediately departed at high speed, porpoising through the water. Striped dolphins are fast swimmers and tend to be easily alarmed. This behavior together with their striped appearance has prompted fisherman to call them 'streakers.' When swimming at top speed, most small cetaceans jump clear out of the water to breath. There are sound hydrodynamic reasons for this. If a whale only partially reveals its body when exposing the blowhole at the surface, it meets maximum resistance, therefore drag is increased, slowing the animal. By jumping clear out of the water it is able to maintain maximum speed, reduce drag and save energy.

The striped dolphin is a relatively common species in the tropical and sub-tropical oceans of the world, however its populations have declined noticeably in recent years. Many populations do not enjoy the same protection as those in Australian territorial waters and are facing several threats throughout their range. This species along with spotted, spinner and common dolphins are still taken in the fishing nets of tuna purse seiners in the eastern tropical Pacific. Striped dolphins are also the primary target of a large drive fishery in Japan and Sri Lanka, where declining numbers suggest hunting is not sustainable. Dolphin 'drive' fisheries take their name from the procedure whereby fisherman round up and trap cetaceans in enclosures before slaughtering them, usually for food and sometimes for bait.

Striped Dolphin surfaces next to the R/V Odyssey.

Photo: Genevieve Johnson

Toxicants or man-made pollutants that are being released into the environment are perhaps the hardest to control and therefore the most insidious threat. A recent massive die-off of striped dolphins in the western Mediterranean was due largely to a fatal viral infection classed as morbillivirus, these animals showed high levels of toxicants in their bodies which probably reduced their body's immune response and could explain this catastrophic die off.

The Odyssey crew have waited almost two years for a second sighting of these beautiful dolphins and we are all hoping we do not have to wait as long to observe and study their behavior again in the wild.

Log by Genevieve Johnson

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