Private Lives of Sperm Whales
For the first time, biologists are disovering the hidden world of sperm whales in the Caribbean
- Photographs by Brandon Cole
- Sep 19, 2012
FEW BIOLOGISTS KNOW as much about sperm whale social behavior as Shane Gero, a doctoral candidate in biology at Dalhousie University in Nova Scotia. He and Dalhousie research professor Hal Whitehead, who has studied whales for more than 30 years, initiated an ongoing study of sperm whales off the Caribbean island of Dominica in 2005. Since then, using photographs of tails, the Dominica Sperm Whale Project has identified more than 400 whales, creating an unprecedented opportunity to study the animals at the individual level.
Sperm whales range throughout the world’s oceans, seas and gulfs. They may dive in excess of 6,600 feet—more than a mile—to hunt squid, their primary food, and can stay under for more than an hour. Male sperm whales grow to about 60 feet long, females to about 40. Much of the blunt head, which can account for a third of body length, is filled with a waxy, oily substance called spermaceti, once used for machine lubrication and for fueling lamps. The species was hunted for centuries for this oil and was especially beleaguered from the end of World War II until 1986, when an International Whaling Commission treaty virtually stopped commercial sperm whale hunting.
National Wildlife asked Gero to discuss recent discoveries about the animals. Following are his responses, accompanied by images of the whales made by Brandon Cole, a Washington-based underwater photographer who spent four weeks in the Caribbean with the massive animals. Patience was a key virtue in getting these images, he says: “You spend hours and hours and hours on a boat looking for whales.” Time observing them, he adds, is a “fly by. You might not see a whale for a few days or a few weeks and then, when you do, it lasts for only a few seconds.” Regardless of the brevity, “It’s pretty amazing to be in the presence of such a large animal.” Some whales have come so close to him, apparently out of curiosity, that he has been able to look into their eyes. “You know there’s something deep and meaningful behind that eye,” he says
Seeking that meaning lies behind both Cole and Gero’s work with whales, as the images show and as Gero reveals in this interview.
National Wildlife: Can you provide a timeline of milestones in a whale’s life?
Gero: Sperm whales are born after a 15- to 18-month gestation. Most nurse for at least 2 years, some for as long as eight. It seems that most don’t start making fluke-up dives [lifting their tails out of the water, the sign of a long foraging dive] until at least 3, but some calves we have followed still rarely lift their tails when they are 7 years old. An adult female sperm whale will spend over 60 percent of her life feeding in the deep ocean. On average, she will spend only about 10 to 15 minutes of every hour in the part of the ocean that sunlight touches.
Both genders are sexually mature in their early teens, which is when many males leave their natal social unit. Males spend the next 15 years wandering, generally moving to colder and colder waters; they range from pole to pole. They do form loose bachelor groups, but little is known about why these form or what role they serve. Sometime around his 30th birthday a male will start making trips to warmer waters, where he’ll rove between units of females to breed.
In contrast, females remain in their natal waters with their families for life. It’s likely that they reproduce soon after maturity. Females can give birth until their forties and maybe beyond. They may live to 70 years or more—no one knows for sure.
NW: What can you tell us about sperm whale social relationships?
Gero: To date, we have identified more than 400 individuals off Dominica. These animals range from Grenada to Guadeloupe and likely much farther, so the population covers much of the eastern Caribbean.
Grandmothers, mothers and their daughters live together for life in groups we call “social units.” Social units in the Pacific can be made up of multiple female lineages, but in Dominica it appears that each is a single female line, so I tend to refer to them casually as families. We have identified more than 20 sperm whale families off Dominica, with an average size of seven individuals—half the size of social units in the Pacific.
NW: How do sperm whales use sound?
Gero: They use it to navigate, find food and communicate with each other. When communicating with each other, they use codas—short patterns of clicks that sound roughly like Morse code. Sperm whale social units have different repertoires or dialects, showing different usage patterns of specific codas. In the Caribbean, we commonly hear the 1+1+3 coda [click-pause-click-pause-click-click-click], but it has never been recorded outside the Caribbean. Calves seem to “babble,” similar to humans, by making a diversity of codas, while adult females in the same unit seem to converge on a common set of a few codas.
Sperm whales use echolocation to find their way around the dark depths of the ocean, just as bats do in the darkness of night. Their echolocation clicks, which are as loud as a jet engine, are used for navigation and for finding prey. The sound bounces off obstacles, and the whales interpret the echoes. We think the first few clicks whales make after diving are used to pick up the bottom. Using hydrophones [underwater microphones], we can hear whales from the surface more than 3 miles away. Given that the average bottom of the ocean is around 2.5 to 3 miles down, it’s likely that sperm whales can “see” the bottom acoustically most of the time.
NW: What threats do sperm whales face?
Gero: Whaling, which continued until the 1980s, reduced the worldwide population of sperm whales to about a third or a quarter of what it once was. Currently, there are about 360,000 sperm whales worldwide. Estimates put the pre-whaling number at around 1.1 million. While harpooning sperm whales has largely stopped, humans still pose major threats to all whales. Chemicals and heavy metals are found in whale tissues from around the world, including those as far away as Antarctica, and whales can become entangled in fishing gear, including longlines and gill nets. Ocean noise, produced by our use of the oceans, is increasingly being seen as a major threat to cetaceans around the world.
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