At Sea, on Course to the Cape Verde Islands
Today was a lovely day at sea, and welcome after several days of activity on the islands of Madeira and the Canaries. We used the time well, with several presentations on the geological history of the islands, the seabirds of the tropical and sub-tropical Atlantic and an introduction to the Aspen Institute discussion seminars planned for the coming days.
We had a number of sightings from the bow of marine mammals and seabirds, including several beaked whales. These enigmatic mammals are usually only seen once and typically at a considerable distance. Once they dive, they are not seen again, so very little is known about them and much of that information has come from strandings of dead animals on shore. However, shortly after lunch today, we had a very nice sighting of a sperm whale. Our expert observer Richard White spotted the animal logging at the surface and Captain Kruess maneuvered National Geographic Explorer slowly toward the whale so that all of us on the bow and on the bridge could get close looks and excellent photographs.
Sperm whales are the largest of the toothed whales and this one appeared to be a large male, about 50-55 feet in length. When sperm whales rest at the surface to replenish their oxygen supply, the behavior is called “logging” because at a distance they look like a log floating on the water. Sperm whales have a single blowhole like all the toothed whales, but in their case it is located at the front of their huge head and on the port side, so that their blow is at an angle of about 45 degrees forward and to port. As they are the only whale which blows this way, once we spot the signature blow the identification is positive. As we approached the animal it continued to log, taking several breaths. Unlike humans, who replace only about 15% of our air supply with each resting breath, sperm whales can exchange perhaps 85-90% of theirs, which makes their breathing much more efficient. They then store the oxygen in the myoglobin in their muscles rather than carrying it in their lungs as they dive. After logging at the surface for several minutes, this whale fluked out and dove, probably for a deep feeding dive which might take it several thousand feet down in search of giant squid, the sperm whales’ favorite prey. So we said goodbye to this magnificent marine mammal and came back to our course for the Cape Verde Islands. All in all, this was a wonderful day at sea, both relaxing and exciting, as well as intellectually stimulating and thoroughly enjoyable.
