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

³ 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.