Rob-servations #8 Sperm whale identification
The sperm whale is the largest toothed whale (odontocete), reaching lengths comparable to some of the baleen whale species. Male sperm whales can reach up to 66 feet (20 meters) in length while females normally do not exceed 40 ft (12 m). This disparity in size is an example of “sexual dimorphism” and is most likely related to the sperm whale’s reproductive behavior. Male sperm whales compete for access to groups of females in a harem-like mating system, thus establishing an evolutionary selection pressure for large body size in males.
Of the cetaceans, sperm whales have long been considered the champion divers, diving longer and deeper than other species (recent research has indicated that Cuvier’s beaked whales may out-perform sperm whales in depth and duration). Some sperm whales have achieved dives of over an hour and to depths of over a mile (1.6km)! Whereas all marine mammals are capable of diving underwater for periods of time, it’s important to remember that diving capabilities vary widely by species. Also, dive depths and durations are dependent on specific activities (e.g., traveling vs. feeding).
Much more could be discussed about sperm whale diving physiology or social behavior. However, the remainder of our discussion will focus on identifying sperm whales while whale watching.
Size and shape of spout / blow: As a large whale, the sperm whale consistently produces a noticeable blow, even when seen from a distance. The interesting feature of the sperm whale’s blow is that it comes out at about a 45-degree angle, rather than straight up as in other whales. As a toothed whale, the sperm whale has a single blowhole. Unlike other cetaceans where the blowhole is located on top of the head along the midline, the blowhole of sperm whales is located asymmetrically at the left front part of the head. This location results in the angled blow. If a whale watcher is located off to the side of the whale, the angled blow is quite evident, aiding in the ability to identify this whale even without seeing the body. As always, be wary of weather conditions. On windy days, the blows of other whales may get “knocked down” and may appear superficially like that of a sperm whale.
Size of animal: As mentioned, the sperm whale is the largest toothed whale. Of the other species of whales in Baja, the humpback, gray, and Bryde’s whales are roughly similar in size. However, there are many field characteristics that distinguish these whales from each other, and certainly distinguish the sperm whale from all other species.
Color: Sperm whales are mostly a uniform gray-brown to almost-black color. Some individuals have white around the lower jaw and along the ventral part of the body. However, we rarely see the jaw and lower body, so these white markings go unseen by most whale watchers.
Dorsal fin: Instead of the classic curved “falcate” dorsal-fin shape that we usually associate with whales and dolphins, the dorsal fin of sperm whales is smooth and rounded, perhaps more of a hump than a fin. Whether we call it a hump or a fin, there is certainly something there, in contrast to the lack of a dorsal fin in the gray whale. Other large cetacean species can be distinguished from sperm whales by the shapes of their dorsal fins.
Tail flukes: Sperm whales quite often show their tail flukes when commencing a dive. Both surfaces of the flukes are typically the same gray-brown color as the body. The flukes have a broad, rounded appearance, as opposed to the more-tapered appearance of a blue whale’s flukes. The trailing edge of the sperm whale’s flukes is smooth, in contrast to the serrated trailing edge of humpback flukes.
Species-specific traits: Sperm whales have several anatomical traits that distinguish them from all other large whales. The shape of the head is quite different from other large whales, comprising about one-third the body length and appearing box-like or squared-off when viewed from the side. We’ve already mentioned the unusual location of the blowhole. The mouth is subterminal, located on the bottom of the head, rather than at the front of the head as in other whales. We rarely see the mouth of sperm whales (although on a 2016 Searcher Natural History Tour a sperm whale swam upside down just below the bow and several people were able to see the narrow lower jaw). The skin of sperm whales has a wrinkly appearance, in contrast to the smooth skin of other whales.
Behavior: We’ve already discussed the fluking behavior of sperm whales, as well as the unique orientation of the blow. We’ve also mentioned the deep diving abilities of these whales. One offshoot of this diving behavior is that sperm whales must spend some time at the surface to physiologically recover from a deep dive. While doing this, they typically are relatively immobile at the surface in a behavior called “logging.” Whaling captains were certainly aware of this behavior and were able to maneuver close to the whales before the whales were fully recovered during their surface interval. While whale watching in Baja, we’ve noticed that some of the whales will start “rocking” their bodies for the last two or three breaths of their surface interval, in preparation for fluking and beginning their next dive.
By understanding the typical dive times of various species, we can tailor our whale-watching strategy to each species. For example, when watching humpback whales on the Gorda Banks, we know that the typical dive is only 8-12 minutes and it’s worthwhile to wait for the whale to re-surface. In contrast, while watching sperm whales, we know that it’s probably not worth waiting around for almost an hour. This is especially true if a group of sperm whales is diving synchronously. If the group is diving asynchronously, then it’s worth standing by, as some whales are diving while others are surfacing and logging.
