Gabriel Barathieu,”Mother and Baby Sperm Whale”, CCBY-SA 2.0
The sperm whale is the largest odontocete, or toothed whale. It has been portrayed frequently in art and literature as a symbol of the great whales, and is best known as the leviathan Moby Dick in Herman Melville’s novel by that name. Sperm whales are among the deepest diving cetaceans, and are found in all oceans of the world. Females and their young travel in permanent units, whereas the much larger males rove between breeding and feeding grounds, as well as among groups of females when breeding.
The sperm whale is the deepest diver of the great whales and can descend to depths of over 5,000 feet (1500 m) and stay submerged for over an hour. Average dives are 30-50 minutes long to a depth of 980-1,970 feet (300-600 m). At such great depths there is little or no solar light. However, organisms at these depths may produce biochemical light (bioluminescence). Sperm whales use their highly developed echolocation ability to locate food and to navigate, making nearly constant clicking sounds that pulse through the water. Sperm whales communicate using “morse-code” like patterns of clicks called codas. There is also a theory that sperm whales may stun their prey with a burst of sound.
The sperm whale’s head houses a large reservoir containing spermaceti, a clear liquid oil that hardens to a wax like consistency when cold, and has long been prized by whalers. Ambergris, a strange substance found in large lumps in the lower intestine of sperm whales, is formed around squid beaks that remain in the stomach. It was used in the making of perfume, and continues to be valuable in spite of its widespread replacement by synthetics.
The head of the sperm whale is blunt and squared off, and has a small, under slung jaw. The head is also large, and makes up to 1/3 the total body length and more than 1/3 of its mass. A single blowhole is located forward on the left side of the head, and the blow, which is bushy, is projected forward rather than straight up as it is with other whales.
Its body has a wrinkled, shriveled appearance, particularly behind the head. The sperm whale is usually a dark, brownish gray with light streaks, spots and scratches. The skin around its mouth, particularly near the corners, is white. The ventral (underside) of the body is a lighter gray and may have white patches.
The sperm whale’s eye does not differ greatly from those of other toothed whales except in size. It is the largest among the toothed whales, weighing about 170 g. It is overall ellipsoid in shape, compressed along the visual axis, measuring about 7×7×3 cm. The cornea is elliptical and the lens is spherical.
Atop the whale’s skull is positioned a large complex of organs filled with a liquid mixture of fats and waxes called spermaceti. Through this complex sperm whales use their highly developed echolocation ability to locate food and to navigate, making nearly constant clicking sounds that pulse through the water. Sperm whales communicate using “morse-code” like patterns of clicks called codas. There is also a theory that sperm whales may stun their prey with a burst of sound.
The brain is the largest known of any modern or extinct animal, weighing on average about 7.8 kilograms (17 lb), more than five times heavier than a human’s, and has a volume of about 8,000 cm3.
The sperm whale’s lower jaw is very narrow and underslung. The sperm whale has 18 to 26 teeth on each side of its lower jaw which fit into sockets in the upper jaw. The teeth are cone-shaped and weigh up to 1 kilogram (2.2 lb) each. The teeth are functional, but do not appear to be necessary for capturing or eating squid, as well-fed animals have been found without teeth or even with deformed jaws. One hypothesis is that the teeth are used in aggression between males. Mature males often show scars which seem to be caused by the teeth. Rudimentary teeth are also present in the upper jaw, but these rarely emerge into the mouth. Analyzing the teeth is the preferred method for determining a whale’s age; analogous to rings in a tree, the teeth build distinct layers of cementum and dentine as they grow.
The sperm whale has a squat dorsal fin, followed by knuckles along the spine. Its flippers are small and slightly tapered, while its flukes are broad, measuring as much as 16 feet (5 m) from tip to tip.
Sperm whales are an acoustically active species, constantly producing echolocation signals to navigate and forage in their deep ocean habitat. In the high latitudes, male sperm whales predominantly use three acoustic signal types: usual clicks, creaks (buzzes), and clangs (slow clicks). Usual clicks and creaks are the most thoroughly studied and understood signals, and are used in echolocation. Little is known about clangs, which have a more resonant ringing quality to them, and have been documented only by males both in the warm tropical breeding grounds and high latitude feeding grounds.
Sound is hypothesized to be generated in vibrations of fatty tissues below the blowhole called the museau de singe, or Monkey Lips. From here, Zimmer et al. theorize that part of the signal escapes through the forehead directly, while the remaining energy is transmitted back through the spermaceti organ, reflects off the frontal air sac, and transmits back through the junk and out the forehead. This occurs within 25-30 milliseconds, made up of 3 or more peaks of energy within a single click or pulse. The diagram below shows the Monkey Lips (Mo) below the Blowhole, with the initial pulse (P0) escaping directly out the forehead, while the remaining energy travels back through the spermaceti organ (So), bouncing off the frontal air sac (Fr), and escaping through the forehead as P1 and P2.
Usual clicks are the most commonly produced signal by sperm whales, and have an Inter-Click-Interval of approximately 1 second. That is, a sperm whale clicks about once every second. This signal is believed to serve a variety of functions including echolocation and communication. Clicks can be detected on an underwater hydrophone over 30 miles away, allowing SEASWAP researchers to track sperm whales at great distances.
Creaks, also referred to as buzzes, are clicks at a very fast repetition rate of about 0.2 seconds. These signals are thought to be associated with foraging, where animals increase their click rate as they hone in on a prey item, terminating in a creak, which also sounds like a buzz. This theory draws from similar echolocation studies done with bats, where echolocation clicks speed up into terminal buzzes when bats hone in on prey items such as moths. These foraging creaks are extremely important to SEASWAP, as they potentially serve as a metric for depredation. Researchers review acoustic data collected on underwater hydrophones to count individual creaks produced by whales during fishing hauls in an attempt to quantify depredation rates.
Clangs are the least understood signal made by male sperm whales in high latitudes, and are referred to in most literature as ‘slow clicks’. The are distinguished by their resonant quality and metallic timbre as well as their slower repetition rate than usual clicks, occurring once every 5-8 seconds. Clangs seem to be produced in clusters or trains, sometimes set apart from usual clicks before and after a train by a silence. They are most likely to be produced on the ascent of dives, or at the surface, rather than on the descent or bottom phase of dives. In the Gulf of Alaska they are thought by SEASWAP researchers to be used in communication, either over large distances, or as a sort of contact call between whales in the same area.
The spermaceti organ is a large, dorsally placed, conical tube filled with liquid spermaceti oil. It is terminated at the front end by one of two tough connective tissue lips, the so-called monkey lips or museau de singe, and at the back end by the frontal air sac that in turn is connected to the right nasal passage. The top and sides of the spermaceti organ are covered by a tough connective tissue sheath, the case, and a complex layer of tendons and muscles innervated by a rich supply of blood vessels and densely packed bundles of motor neurons.
The spermaceti oil in the junk complex is contained in a sponge-like tissue structure where so-called wafers of tissue with higher oil content are interspaced by a connective tissue matrix with lower oil content. Compared to the spermaceti organ, this structure made the oil extraction considerably more difficult for the whalers, hence the term “junk.”
Kurzon, “Sperm Whale Distribution (Pacific equirectangular), CC BY-SA 3.0
Sperm whales are found in all oceans of the world and are widely distributed across the entire North Pacific. They were subjected to two waves of commercial whaling and were heavily exploited in the North Pacific, until the late 1970s. Although sperm whale catches in the Gulf of Alaska overall were lower than other areas in the North Pacific, in one year, 1964, over 1,800 sperm whales were removed in the Gulf of Alaska alone, north of 50° N. No sperm whales were removed in this area by the Soviet catcher fleet after 1967. Although sperm whale numbers have likely increased and possibly recovered since the cessation of commercial whaling, they continue to be listed as an endangered species in U.S. waters.
Some data exists on sperm whale year round presence in the Gulf of Alaska from acoustic recordings from bottom-mounted recorders However, these data could not be used to determine whether the same sperm whales were present year round representing a stable population or if vocalizations were from multiple transitory whales passing through the area.
Population structure is poorly understood and has been the subject of debate for decades. Low genetic diversity worldwide provided little basis for differentiating groups of whales, however, in 2011, researchers revisited the population structure for sperm whales in the North Pacific using new methodologies. These results revealed whales present in the California Current are differentiated genetically where sperm whales from the Hawaiian Archipelago and the eastern tropical Pacific could not be fully differentiated. The results were clear that the high latitude male sperm whales in Alaska originated from not one but multiple populations. While application of genetic techniques is promising it will be challenging and perhaps impossible, to define populations of sperm whales geographically. This may be particularly true for males who, when sexually and physically mature, roam widely with reported movements over 5,000 km and may not return to breed in the ocean where they were born. Essentially, while some genetic distinctions exist among sperm whale populations, it is still an emerging story.
One of the largest gaps in our understanding of sperm whales is movements of the males. How mature males move throughout the oceans will define and influence mating strategies and gene flow. Male movement consists of gradual movement to higher latitudes with age for periodic, but not necessarily seasonal, transits occur between the lower latitude feeding/breeding grounds and higher latitude feeding grounds. These males have variable patterns of movement while at high latitudes and move almost continually at low latitudes, with repeat visitation to groups of females. Clearly, male movements are complex, with individual variability over large temporal and spatial scales.
Males reach sexual maturity at approximately 33-39 feet (10-12 m), and 10 years or more of age but do not seem to take an actual part in breeding until their late 20’s. Females reach sexual maturity at 27-29 feet (8-9 m), and 7-13 years of age. Gestation is 14-16 months. Newborn calves weigh approximately 1 ton (907 kg), and are 11-16 feet (3.4-4.9 m) long. Calves nurse up to two years or longer. Contrary to earlier belief, sperm whales do not seem to have harems. Instead, large males only attend female groups a few hours at a time. These female groups (family groups) consist typically of 10-20 animals. Within these groups there appears to be communal care for the young.
Sperm whales’ main source of food is medium-sized deep water squid, but they also feeds on species of fish, skate, octopus, and smaller squid. The diet of sperm whale populations in the open ocean includes more squid, while coastal populations mainly forage on fish. Stomach samples examined at whaling stations from whales caught in Alaska revealed that squid was an important food in the Western Aleutians and Bering Sea, but fish became progressively more important towards the eastern Aleutians and into the Gulf of Alaska. Fish eaten in northern latitudes commonly included sharks, sea devils, cod and hake. A sperm whale consumes about one ton (907 kg) of food each day.
A sperm whale’s lower jaw contains 18-25 large teeth on each side of the jaw, 3-8 inches in length. The upper jaw may have tiny teeth but they rarely erupt. The upper jaw contains a series of sockets into which the lower teeth fit.
Sperm whales are still fairly numerous, but selective killing of the larger breeding-age males over many years upset the male-to-female ratio, and the birth rate has seriously declined in some populations. The average size of sperm whales killed noticeably decreased during the last 40 years of hunting. Sperm whales are listed as an endangered species. The current population in the Gulf of Alaska is unknown.
Sperm whales were killed in two massive waves of commercial whaling, the Moby Dickwhalers who worked mainly between 1740-1880, and the modern whalers whose operations peaked in 1964, when 29,255 were killed. Whaling took a heavy toll on sperm whales in the eastern North Pacific, including Alaskan waters, until 1986. Most recent estimates suggest a global population of about 360,000 animals down from about 1,100,000 before whaling.
For management, the International Whaling Commission (IWC) recognizes two stocks in the North Pacific (eastern and western). However, the IWC has not reviewed this stock boundary in many years. For the Marine Mammal Protection Act stock assessment reports, sperm whales within the Pacific U.S. Exclusive Economic Zone (EEZ) are divided into three discrete, non-contiguous areas: (1) California, Oregon and Washington waters, (2) waters around Hawaii, and (3) Alaska waters. Genetic analyses are currently underway to examine these presumed stock boundaries. A few recently obtained Alaska samples are being added to the analyses. To date, the Southwest Fisheries Science Center (SWFSC) has examined boundaries for the CA/OR/WA stock, finding significant differences from animals sampled to the south but no clear picture to the west or north.
American Cetacean Society Fact Sheet
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