Physeter macrocephalus Linnaeus 1758
Order Cetacea : Family Physeteridae
DESCRIPTION. A large, blackish-brown whale with huge head and truncate snout; lower jaw small, long, and slender, the symphysis extending half the length of the ramus; the single blowhole on anterior left edge of snout; no dorsal fin but conspicuous hump; eye very small, low, and near angle of mouth; pectoral fin short and relatively broad; upper jaw lacking functional teeth; lower jaw with 22–24 large, sharp teeth on each side. Total length of males up to 20 m; females much smaller. Weight of a male 13 m long was 39 metric tons.
DISTRIBUTION. Sperm whales are worldwide in distribution and occur in all oceans, including Arctic and Antarctic waters, but they are primarily found in temperate and tropical waters of the Atlantic and Pacific Oceans. Sperm whales are the most numerous of the great whales in the Gulf of Mexico, and from the mid-1700s to the early 1990s they were hunted in the region. Most aerial and shipboard sightings are from the continental edge and upper continental slope. Estimates suggest there are between 300–400 sperm whales in the northwestern Gulf. Stranded animals have been found along the Texas coast. Four strandings, from Cameron, Nueces, and Kleberg counties, were recorded during the most recent stranding period (2002–2014).
SUBSPECIES. Monotypic species.
HABITS. Sperm whales are highly migratory, especially the males. Adult males move into high-latitude temperate waters during summer, leading a solitary lifestyle, while females remain grouped in tropical or subtropical waters. In winter, the bulls return to lower latitudes for mating.
These whales regularly dive to depths of 1,000 m (3,281 ft.) but are known to reach depths of >2,100 m (>6,890 ft.) and may be capable of dives to 3,000 m (9,843 ft.). At such depths these remarkable animals hunt their primary prey, squid. Much speculation has arisen concerning the feeding method of sperm whales, as no light penetrates to those depths and squid are highly elusive swimmers. The whales may feed by ambushing prey as they lie relatively motionless near the ocean floor, attracting squid with a bioluminescent glow emanating from the whale's mouth, or perhaps by stunning prey with ultrasonic sounds. Because of the great depths at which these animals feed, the exact method of the sperm whale's feeding habits has yet to be determined. These whales are known to produce a variety of click sounds occurring in sequence and termed codas. Such sounds are probably used in echolocation and may play an important role in locating prey while feeding.
Up to 1 metric ton of squid per day is required to sustain a single sperm whale. Besides squid, these whales occasionally consume other deepwater prey, including octopuses, lobsters, crabs, jellyfish, sponges, and several varieties of fish.
Breeding behavior in sperm whales is similar to harem formation; a single, dominant male accompanies a group of females and defends the group against competing males. During this time, smaller males are driven off to form their own bachelor groups, and battles between rival males for control of the harem may occur. A harem may comprise 20–30 females, but many of them may already be pregnant or tending young. The gestation period is approximately 15 months, the period of lactation is 1–2 years, and there is a resting period of up to 10 months following weaning before the females will mate again. The breeding cycle, therefore, may take as long as 5–7 years. Newborn sperm whales are about 4 m in length and weigh approximately 1 metric ton. Although twin calves are known, a single calf per female is believed the rule. Sexual maturity is reached at about 10 years of age.
Sperm whales were once the mainstay of the pelagic whaling industry. Before the advent of cannon harpoons, diesel-powered catcher boats, and massive factory ships, the hunting of sperm whales was a dangerous occupation. Sperm whales are known to have effectively fought back on occasion; one even sank an American whaler, the Essex, in 1820. In spite of the danger, sperm whales were hunted the world over for the array of valuable products they contained: whale oil for lamps and lubricants; spermaceti (oil from the forehead) for high-quality, smokeless candles; and ambergris, a waxy by-product of digestion, which was used in the manufacture of fragrances. By the early twentieth century, whaling had become an efficient, wide-open business that threatened not only the sperm whale but all of the other great whales with extinction. Finally, in the 1970s, whaling was banned worldwide.
POPULATION STATUS. Common; strandings and observations. Sperm whales are by far the most numerous large whale in the Gulf of Mexico, and they have been stranded or sighted in every month of the year. These factors suggest that a stock of sperm whales is unique to the Gulf of Mexico, which now has been confirmed through photo-identification studies. Estimates from the GulfCet project indicates that there are between 300 and 400 sperm whales in the northwestern Gulf of Mexico. They have been sighted (and their clicks heard via hydrophones) in all parts of the northwestern Gulf between the 100 and 2,000 m (328–6,562 ft.) depth contours. However, the greatest concentrations were around the 1,000 m (3,281 ft.) depth contour south of the Mississippi River Delta and at similar depths roughly 300 km (186 mi.) east of the Texas–Mexico border.
CONSERVATION STATUS. The USFWS lists the sperm whale as endangered, but it is not on the TPWD list. The IUCN lists it as vulnerable because commercial whaling at a large scale over the last three generations has resulted in a global population decline. Now that whaling has virtually stopped, the population is thought to be recovering. The stranding of an infant sperm whale, nicknamed Odie, near Sabine Pass, Texas, on 2 September 1989 made national headlines. The young whale was estimated to be >2 weeks old and was transported by truck to Sea-Arama in Galveston, where it died 1 week later from a lung infection.
From The Mammals of Texas, Seventh Edition by David J. Schmidly and Robert D. Bradley, copyright © 1994, 2004, 2016. Courtesy of the University of Texas Press.