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The Mammals of Texas - Online Edition

ORDER CETACEA:

WHALES, PORPOISES, AND DOLPHINS

Small to extremely large, hairless, fish-shaped mammals that are adapted strictly to an aquatic habitat; front limbs modified as flippers or fins, hind limbs absent, except for vestigial internal remnants; eyes and ears small, the latter valvular and lacking external parts; skull telescoped so that nostrils open on top of head through a single or double blowhole; no vocal apparatus, the so-called roar being produced by expelled air; soft palate and epiglottis so modified that nasal cavities connect directly with lungs and not with mouth; tail lengthened and dermal elements expanded into broad, flattened flukes; mammary glands situated on either side of vaginal opening, the single teat lodged in a slitlike recess; penis and testes contained within the body integument; skin glands, except for conjunctival and mammary, lacking; teeth present or absent.

This group contains the largest of all known mammals, living or extinct. The blue whale sometimes reaches a length of 33 m and may weigh up to 135 metric tons. As a group whales are slow breeders — one young every 2 years is generally the rule. The teat in a 15-m whale is no larger than a man’s thumb, and the mouth of the young calf is so constructed that it cannot suck. Perhaps the milk is forced into the mouth of the baby by contraction of muscles over the udder or by the "butting" of the young one. In a freshly killed, lactating female palpation of the udder may force out jets of cream-colored milk.

Cetaceans have no voice but many produce distinct sounds used in mating rituals, communication, and echolocation. Such sounds are specific in character and many are audible for distances of a kilometer or more. Bats and cetaceans are the only mammals known to echolocate; they use sound emissions and echoes to form mental images of their surroundings.

Many of the whales have retained teeth in both jaws. Some have retained them in the lower jaw only, whereas others have lost them completely and have developed instead peculiar structures termed baleen or whalebone. These are elongated, flattened, leaflike modifications of the ridges in the roof of the mouth. Two series of plates, one on each side, hang from the roof of the mouth and the long, fibrous, hairlike structures on the inner edge of one plate overlap with those of its neighbor in such a way that an efficient sieve is produced. All whales with such structures feed on small organisms strained from the water. Toothed whales feed on larger animal life: fish, seals, or even other whales.

The spout is characteristic of many species. It is produced by expelling moisture-laden air from the lungs into the air. As the air escapes it cools, condenses, and becomes visible if the temperature of the outside air permits and then quickly dissipates. When not in use, the blowholes are closed by external flaps that prevent water from entering the lungs. All whales must come to the surface to breathe; if they are forced to remain submerged, they drown.

Many whales and porpoises live near the coast, frequenting shallow water, but a large number of them are pelagic and roam the open seas. Many of the latter perform regular migrations. In winter they inhabit temperate or tropical waters where they mate and give birth to their young a year later; in summer they move to the Arctic or Antarctic seas among the ice floes. Most of the food in the ocean is produced where cold and warm streams meet and it is there that whales flock in great numbers.

Twenty-nine species of cetaceans have been documented within the Gulf of Mexico. This assemblage includes approximately 40% of the genera and 35% of the cetacean species in the world. Twenty-six of the 29 Gulf species have either stranded on Texas beaches or been observed at sea in the waters of the western Gulf.

The terms whale, dolphin, and porpoise need explanation. As here used, the term whale is all-inclusive and may be applied to any cetacean. The term dolphin applies to those small whales that have a distinct snout or beak and numerous conical teeth that are roughly circular in cross-section. The term porpoise applies to those small, blunt-nosed whales that have flat, spade-shaped teeth. Based on these definitions, all the small, beaked whales in Texas waters with numerous conical teeth are dolphins. No porpoises are known to occur in Texas waters.

One of the more interesting biological aspects about marine mammals, especially cetaceans, is their propensity to strand — to ground or beach themselves out of water and be unable to return under their own power. Generally, there are two types of strandings — those of a single individual, which are by far the most prevalent, and multiple or mass (two or more animals) strandings, excluding parent/offspring combinations. The study of marine mammal strandings is a subject of considerable interest to scientists and the general public, and stranding studies have proven to be an undeniably good source of information, perhaps the only information, about aquatic mammals that exists.

A Texas Marine Mammal Stranding Network was organized in 1980, as a means of discovering, gathering, and reporting information of marine mammals stranded along the Texas coast. It also assists live stranded animals, administering first aid and transporting them to facilities where they can be treated. The network consists of scientists, students, federal and state agencies, marine veterinarians, and other interested individuals.

From October, 1980, through May, 1987, the Texas Marine Mammal Stranding Network documented a total of 501 cetacean strandings. Of these, 87% were represented by bottlenose dolphins, the most common inshore species. Live strandings accounted for only 7% of all strandings, and a majority of these occurred near Port Aransas where deeper waters are closer to shore. There was only one known instance of a mass stranding, that of a group of pygmy killer whales.

Although there has been much speculation and theorizing, scientists do not completely understand why cetaceans beach themselves. Oftentimes when live strandings are observed, attempts to return the animals to sea fail. Many, upon release, simply turn and head for shore once more. Undoubtedly, many factors may account for this "suicidal" form of behavior. Among the possible causes suggested for strandings are: parasites, disease, and illness; choking on ingested objects; wounds from gunshots and boat and ship encounters; difficulties in the birth process; starvation; bad or rough weather; seaquakes, tremors, and underwater explosions; pollution; net entanglements associated with commercial fishing; fouled sonar systems; and panic caused by the pursuit of other animals (predators). Social facilitation or as it is more commonly known, the "follow the leader" theory, is widely given as a reason for mass strandings. Social facilitation involves a cohesive group behavior whereby a dominant individual suddenly beaches itself causing the whole group to follow suite and do likewise.

Family Balaenidae (right whales)

Northern Right Whale, Eubalaena glacialis

Family Balaenopteridae (rorquals or baleen whales)

Minke Whale, Balaenoptera acutorostrata
Bryde’s Whale, Balaenoptera edeni
Blue Whale, Balaenoptera musculus
Fin Whale, Balaenoptera physalus
Humpback Whale, Megaptera novaeangliae

Family Physeteridae (sperm whales)

Sperm Whale, Physeter macrocephalus
Pygmy Sperm Whale, Kogia breviceps
Dwarf Sperm Whale, Kogia simus

Family Ziphiidae (beaked whales)

Blainville’s Beaked Whale, Mesoplodon densirostris
Gervais’ Beaked Whale, Mesoplodon europaeus
Cuvier’s Beaked Whale, Ziphius cavirostris

Family Delphinidae (toothed whales and dolphins)

Killer Whale, Orcinus orca
False Killer Whale, Pseudorca crassidens
Pygmy Killer Whale, Feresa attenuata
Short-finned Pilot Whale, Globicephala macrorhynchus
Melon-headed Whale, Peponocephala electra
Rough-toothed Dolphin, Steno bredanensis
Common Dolphin, Delphinus delphis
Risso’s Dolphin, Grampus griseus
Bottlenose Dolphin, Tursiops truncatus
Pantropical Spotted Dolphin, Stenella attenuata
Clymene Dolphin, Stenella clymene
Striped Dolphin, Stenella coeruleoalba
Atlantic Spotted Dolphin, Stenella frontalis
Spinner Dolphin, Stenella longirostris


KEY TO THE WHALES AND DOLPHINS OF THE TEXAS COAST

1.
  • No teeth present; baleen plates in upper jaw; twin blowholes; skull symmetrical; no mandibular symphysis (baleen whales): 2
  • Teeth present (although sometimes not erupted); no baleen plates; single blowhole; skull slightly to moderately asymmetrical; mandibular symphysis present (toothed whales): 8
2.
  • Dorsal fin and ventral throat grooves present; no growths on top of head; upper jaw relatively flat when viewed from the side and broad from the top: 3
  • No dorsal fin or ventral throat grooves; crusty growths (callosites) present on head; upper jaw arched when viewed from the side and relatively narrow from the top: Eubalaena glacialis (northern right whale).
3.
  • Throat grooves end well before navel: 4
  • Throat grooves extend to or beyond navel: 5
4.
  • 50-70 ventral grooves, longest ending between flippers; 231-285 white or yellowish-white baleen plates per side, less than 21 cm long; conspicuous white bands on flippers; maximum body length 9 m: Balaenoptera acutorostrata (Minke whale).
  • 32-60 ventral grooves, longest ending well short of navel; 219-402 pairs of black baleen plates, less than 80 cm long; flippers totally dark; maximum body length 16 m: Balaenoptera borealis (Sei whale).
5.
  • Flippers more than 25% of body length, heavily scalloped on the leading edge, and marked on the underside with a variable pattern of white: Megaptera novaeangliae (humpback whale).
  • Flippers less than 25% of body length, smooth on the leading edge, and without a distinct pattern of white on the underside: 6
6.
  • Head with only one prominent ridge from blowhole to snout; 55-100 ventral grooves; maximum body length more than 20 m: 7
  • Head with series of three parallel ridges from blowhole to snout; 40-50 ventral grooves; maximum body length less than 15 m: Balaenoptera edeni (Bryde’s whale).
7.
  • Head broad and almost U-shaped from above; dorsal fin very small (< 33 cm) and set in the last one-third of back; 270-295 black baleen plates per side; coloration of head symmetrical; body mottled gray; maximum body length 26 m: Balaenoptera musculus (blue whale).
  • Head V-shaped and pointed at tip as viewed from above; dorsal fin up to 61 cm tall and set more than one-third forward from fluke notch; 260-480 white to gray baleen plates per side; head coloration asymmetrical (left side gray, much of right side white); back dark, with light streaks; maximum body length 24 m: Balaenoptera physalus (fin whale).
8.
  • Upper jaw extending well past lower jaw; lower jaw very narrow: 9
  • Upper jaw not extending much or at all past lower jaw; lower and upper jawabout the same width: 11
9.
  • Body length 4-18 m; head squarish and large, up to one-third of body length; blowhole at left side of front of head; low roundish dorsal hump present, followed by a series of bumps; 18-25 teeth in each side of lower jaw, fitting into sockets in upper jaw: Physeter macrocephalus (sperm whale).
  • Body length less than 4 m; head much less than one-third of body length; blowhole set back from front of head; prominent dorsal fin present; 8-16 teeth in each side of lower jaw: 10
10.
  • Throat creases generally absent; dorsal fin small and located in last one-third of body; distance from tip of snout to blowhole greater than 10.3% of total length; 12-16 (rarely 10-11) teeth in each half of lower jaw: Kogia breviceps (pygmy sperm whale).
  • Two small creases present on throat; dorsal fin generally tall and located near midpoint of back; distance from tip of snout to blowhole less than 10.2% of total length; 8-11 (rarely up to 13) teeth in each side of lower jaw: Kogia simus (dwarf sperm whale).
11.
  • Two conspicuous grooves on throat; notch between flukes absent or indistinct; enlarged teeth numbering no more than two pairs in lower jaw (beaked whales): 12
  • No conspicuous grooves present on throat; prominent median notch in flukes; teeth present in both upper and lower jaws (dolphins and toothed whales): 14
12.
  • One or two pairs of teeth at or near tip of lower jaw, erupted only in some adults; beak indistinct; head small relative to body size; body to at least 7 m long: Ziphius cavirostris (Cuvier’s beaked whale).
  • One pair of teeth well behind tip of lower jaw, erupted only in adult males; moderate beak, not sharply demarcated from forehead; body to 4-5 m long: 13
13.
  • Tooth positioned approximately 7.5-10 cm from tip of mandible (one-third the length of mandible): Mesoplodon europaeus (Gervais’ beaked whale).
  • Tooth positioned at midpoint of mandible on bony prominences near corners of mouth: Mesoplodon densirostris (Blainville’s beaked whale).
14.
  • Beak not sharply delineated from head by a distinct crease: 15
  • Beak sharply delineated from head by a distinct crease: 21
15.
  • Head blunt, with no prominent beak: 16
  • Head long and conical but beak runs smoothly into forehead, with no crease; body dark gray to black above and white below with narrow cape on back: Steno bredanensis (rough-toothed dolphin).
16.
  • Head divided medially by a heavy vertical crease; coloration gray with heavy scarring in the form of numerous scratches; no teeth in upper jaw (1-2 rarely present), 0-7 teeth present in each side of lower jaw: Grampus griseus (Risso’s dolphin).
  • Head not divided by a vertical, median crease; body coloration predominantly black with some white markings; teeth (7 or more pairs) in both upper and lower jaws: 17
17.
  • Striking black and white coloration, with white postocular patches, white lower jaw, and light gray saddle behind dorsal fin; dorsal fin tall and erect (up to 0.9 m in females and 1.8 m in males); flippers large and paddle-shaped; 10-12 large oval teeth (2.5 cm in diameter) in each tooth row; body to at least 9 m long: Orcinus orca (killer whale).
  • Coloration predominantly black with little, if any, gray or white markings; dorsal fin less than 0.5 m in height; flippers long and pointed to slightly rounded at tips; body never more than 7 m long and often considerably less: 18
18.
  • Low, broad-based dorsal fin located on forward third of back; head bulbous; body black, with light anchor-shaped patch on belly and often light gray saddle-shaped flippers, one-fifth to one-sixth of body length; 7-9 pairs of teeth in front half of each tooth row; body to about 7 m long: Globicephala macrorhynchus (short-finned pilot whale).
  • Dorsal fin located near midpoint of back; body never more than 5.5 m long: 19
19.
  • Flippers with distinct hump on leading edge giving S-shaped appearance; body predominantly black; 7-12 large teeth in each half of both jaws; body to at least 5.5 m long: Pseudorca crassidens (false killer whale).
  • Flippers lack hump on leading edge and not S-shaped; body predominantly black but with some white markings on belly and chin or lips; 8-25 teeth in each half of the jaws; body considerably less than 5 m long: 20
20.
  • Fewer than 15 teeth in each half of both jaws; flippers rounded at tip; body mostly black with white belly patch which may extend onto sides in area of anus; head rounded from above; body to almost 3 m long: Feresa attenuata (pygmy killer whale).
  • More than 15 teeth per side of each jaw; flippers sharply pointed at tip; body black to brownish black on back, light gray on sides, light gray to white on belly, lips often white; head triangular from above; body to at least 2.7 m long: Peponocephala electra (melon-headed whale).
21.
  • Body coloration dark gray on back, lighter gray on sides, with white to pink belly; no stripes or spots; beak relatively short and thick; 20 to 26 teeth present in each side of upper jaw and 18 to 24 teeth present in each side of lower jaw: Tursiops truncatus (bottlenose dolphin).
  • Body coloration includes numerous spots, mottling, or stripes; beak relatively long and slender; up to 200 total teeth present in mouth: 22
22.
  • Body coloration heavily mottled with light or dark spots: 23
  • Body coloration without spots but traversed by one or more longitudinal stripes: 24
23.
  • Coloration characterized by "spinal blaze" sweeping up and back below the dorsal fin; peduncle not divided into upper dark and lower light halves; no black stripes connecting eyes and flipper with jaws; background of dark ventral spots is white; total number of vertebrae, 67-72: Stenella frontalis (Atlantic spotted dolphin).
  • Coloration not characterized by a "spinal blaze"; peduncle divided into upper dark and lower light halves; dark stripe from flipper to lower jaw; background of dark ventral spots is gray; total number of vertebrae, 74-84: Stenella attenuata (pantropical spotted dolphin).
24.
  • Light gray, tan, or yellow stripes crisscross on sides; palate with deep grooves bordering upper teeth: Delphinus delphis (common dolphin).
  • Stripes do not crisscross; palatal groove shallow or absent: 25
25.
  • Black stripes extending from eye to anus, eye to flipper, and from above flipper toward belly; 43 to 50 teeth present in each side of both jaws: Stenella coeruleoalba (striped dolphin).
  • Black side stripes absent: 26
26.
  • Dark-colored rostrum with gray or white "moustache" area; chin white to cream-colored; tip of upper jaw to apex of melon less than 12 cm; seldom more than 46 teeth in each side of the jaw: Stenella clymene (Clymene dolphin).
  • Dark rostrum without "moustache"; tip of upper jaw to apex of melon more than 12 cm; chin gray to black; usually more than 46 teeth in each side of the jaw: Stenella longirostris (spinner dolphin).

The Sei whale is not included in the species accounts because there are no confirmed records of this species from the Texas coast. However, it is possible that this species could occur in the region and has therefore been included in this key.