ORDER CETACEA

WHALES, PORPOISES, AND DOLPHINS

These mammals are adapted strictly to an aquatic life and may be characterized as follows: small to extremely large, hairless, fish-shaped mammals; 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 slit-like recess; penis and testes contained within the body integument; skin glands, except for conjunctival and mammary, lacking; teeth present of absent. 

Living cetaceans are traditionally divided into two suborders: the Odontoceti, individuals that have teeth and an asymmetrical skull; and the Mysticeti, individuals that have plates of baleen instead of teeth and a symmetrical skull.  Representatives of both suborders have been recorded in the Gulf of Mexico. 

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 forced 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, leaf-like 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, hair-like 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, such as 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 the 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 pelagic species perform regular migrations.  In winter, they inhabit temperate or tropical waters where they mate and give birth to their young 1 year later; in summer they move to the Arctic or Anarctic seas among the ice flows.  Most of the food in the ocean is produced where cold and warm streams meet, and it is there that whales gather in great numbers. 

Twenty-eight species of cetaceans have been documented within the Gulf of Mexico, and all but one is known from Texas waters.  Three other species may occur in the Gulf of Mexico but have not yet been documented.  This assemblage includes approximately 40% of the genera and 35% of the cetacean species in the world. 

The terms "whale", "dolphin", and "porpoise" need explanation.  As used herein, whale is all-inclusive and may be applied to any cetacean.  Dolphin applies to those small whales that have a distinct snout or beak and numerous conical teeth that are roughly circular in cross section.  Porpoise applies to those small, blunt-nosed whales that have flat, spade-shaped teeth.  Based on those 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 of 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 strandings of more than two animals, excluding parent offspring combinations.  Cetacean strandings are a subject of considerable interest to scientists and the general public, and stranding studies have proven to be an undeniably good source of information about aquatic animals. 

The 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 1987 through 2001, 2,300 strandings were documented for the Texas Gulf Coast.  Of those, 93% were represented by bottlenose dolphins, the most common inshore species.  Thirty-three percent of strandings occurred in Galveston County.  Live strandings accounted for only 3% of all strandings.  Most live strandings occur near Port Aransas, where deeper waters are closer to shore.  Years of particularly high die-offs have been correlated with various causes, including freezing temperatures, pesticide runoff, and viruses. 

From 2002 through 2014, 1,805 strandings were documented along the Texas coast.  Of those, 94% were represented by bottlenose dolphins.  Thirty-eight percent of strandings occurred in Galveston County.  Live strandings accounted for 6% of all strandings, and most of them occurred in Galveston County.  In summary, the stranding tabulations for this period were remarkably similar to those from 1987-2001 time frame. 

Although there has been much speculation and theorizing, scientists do not completely understand why cetaceans beach themselves.  When live strandings are observed, attempts to return the animals to sea frequently fail.  Many, when released, 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 by 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 cohesive group behavior that causes an entire group to follow suit when a dominant individual suddenly beaches itself. 

Data on the distribution of offshore species in the deeper waters of the Gulf began to accumulate with the deployment of dedicated large-scale aerial and boat surveys that began in the later 1970s and continued through the end of the century.  The most extensive survey of cetaceans in the offshore waters (100-2,000 m [328-6,562 ft.] deep) of the northern Gulf was conducted jointly by the National Marine Fisheries Service (NMFS), the Southeast Fisheries Center (SEFSC) of the NMFS, and Texas A&M University during 1991-1998 and was called the GulfCet surverys.  The first part of the project (GulfCet I) was conducted from 1991 to 1995; its main objective was to determine the distribution and abundance of cetaceans along the continental slope in the north-central and western Gulf, that is, in areas that could be affected by future oil production.  A continuation of the project (GulfCet II) ran from 1996 to 1998, with the main goal being to identify possible associations between cetacean high-use habitats and mesoscale environmental variability.  Shipboard surveys were started by the SEFSC in 1991 and continued through 2004; results were published in a number of reports and papers. 

A major milestone in the knowledge about Gulf marine mammals came in 2000 with the publication of the book The Marine Mammals of the Gulf of Mexico, authored by Bernd Würsig, Thomas A. Jefferson, and DJS.  This single reference summarized the information from the stranding records together with that of the aerial and boat surveys (emphasizing the GulfCet surveys) about the distribution, abundance, and life histories of marine mammals in the region.  This book constitutes the primary reference for much of the information presented in this volume.  The interested reader is referred to this reference for additional information about cetaceans in the Gulf. 

In 2009, DJS and Würsig published an updated synopsis of marine mammals, emphasizing cetaceans, from the Gulf of Mexico as part of a larger volume, Gulf of Mexico Origins, Waters, and Biota, Volume 1, Biodiversity (Darryl L. Felder and David K. Camp, editors; Texas A&M University Press).  The chapter by DJS and Würsig included a checklist that summarized aspects of the status of the cetaceans in the Gulf of Mexico according to several categories -- habitat and biology, range of depth (m) of occurrence, overall geographic range, and Gulf of Mexico range.  Much of that information has been incorporated into the species accounts in this new edition of The Mammals of Texas.  

From a biogeographic perspective, representatives from four geographic assemblages of species occur in the Gulf, including cosmopolitan, eurythermic species; endemics to the Atlantic Ocean; pantropical warm-stenothermal species; and antitropical, cold-stenothermal species. 

Of the 27 cetacean species recognized for the Texas waters of the Gulf, 9 are cosmopolitan species that occur in most major oceans and for the most part are eurythermic with a broad range of temperature tolerances.  They are the common minke whale, Balaenoptera acutorostrata; sperm whale, Physeter macrocephalus; pygmy sperm whale, Kogia breviceps; dwarf sperm whale, Kogia sima; Cuvier's beaked whale, Ziphius cavirostris; Blainville's beaked whale, Mesoplodon densirostris; killer whale, Orcinus orca; Risso's dolphin, Grampus griseus; and common bottlenose dolphin, Tursiops truncatus.  

Three species (Gervais's beaked whale, Mesoplodon europaeus; Atlantic spotted dolphin, Stenella frontalis; and Clymene dolphin, Stenella clymene) have a distribution confined to the Atlantic Ocean.  All have stranded on Texas beaches or have been sighted near our beaches at one time or another. 

Ten cetaceans have distributions peculiar to tropical, warm waters of both hemispheres and may be considered warm-stenothermal forms.  They include Bryde's whale, Balaenoptera brydei; short-finned pilot whale, Globicephala macrorhynchus; false killer whale, Pseudorca crassidens; pygmy killer whale, Feresa attenuata; melon-headed whale, Peponocephala electra; rough-toothed dolphin, Steno bredanensis; pantropical spotted dolphin, Stenella attenuata; spinner dolphin, Stenella longirostris; striped dolphin, Stenella coeruleoalba; and Fraser's dolphin, Lagenodelphis hosei.  All but Bryde's whale have stranded on Texas beaches. 

Five species (North Atlantic right whale, Eubalaena glacialis; blue whale, Balaenoptera musculus; fin whale, Balaenoptera physalus; sei whale, Balaenoptera borealis; and humpback whale, Megaptera novaeangliae) have distinct bipolar (antitropical) distributions and are regarded as cold-stenothermal forms based on where they feed.  The humpback whale, however, enters tropical waters to breed.  All of these species, except for the sei whale, also have stranded on Texas beaches. 

At least seven of the Texas cetacean species are migratory, including several species of rorquals (the blue, fin, sei, and minke whales), the humpback, and the North Atlantic right whales.  These species generally travel between a breeding zone in which they do not eat and a feeding zone of high productivity in cooler waters.  With the exception of the common minke whale, all of these great whales are thought to be extralimital, or of accidental occurrence, in the Gulf.  The sperm whale is known to be migratory in other parts of the world, but female groups appear to be year-round residents in the Gulf of Mexico. 

The most common species in the bays and near shore along the Texas coast is the common bottlenose dolphin, Tursiops truncatus, and they are regularly seen in bays, ship channels, and even estuaries.  As one moves onto the continental shelf, bottlenose dolphins and Atlantic spotted dolphins (Stenella frontalis) are the dominant species, and the oceanic community of the northern Gulf nearest to the Texas coast comprises 19 additional species: Bryde's whale (Balaenoptera brydei); sperm whale (Physeter macrocephalus); dwarf sperm whale (Kogia sima); pygmy sperm whale (K. breviceps); Cuvier's beaked whale (Ziphius cavirostris); Blainville's beaked whale (Mesoplodon densirostris); Gervais' beaked whale (M. europaeus); melon-headed whale (Peponocephala electra); pygmy killer whale (Feresa attenuata); false killer whale (Pseudorca crassidens); killer whale (Orcinus orca); short-finned pilot whale (Globicephala macrorhynchus); rough-toothed whale (Steno bredanensis); Risso's dolphin (Grampus griseus); Fraser's dolphin (Lagenodelphis hosei); pantropical spotted dolphin (Stenella attenuata); striped dolphin (S. coeruleoalba); spinner dolphin (S. longirostris); and Clymene dolphin (S. clymene). 

Several cetaceans are rare in the Gulf; including, with one possible exception, all of the baleen whales and all of the beaked whales.  Only Bryde's whale (Balaenoptera brydei), a baleen whale that is a year-round inhabitant of tropical and subtropical waters, occurs with any regularity.  Records are scattered throughout the year, suggesting it is likely that the Gulf represents at least a portion of the range of a dispersed, resident population of Bryde's whales.  Most of the sightings have been from the northeastern Gulf along the shelf edge near De Soto Canyon. 

There are a substantial number of sightings of sperm whales (Physeter macrocephalus) in the Gulf.  Sperm whales have stranded or been sighted in all months and seasons of the year.  Most sightings are from deep water beyond the edge of the continental shelf, although there are a few records from over the shelf, such as the Mississippi River Delta.  The Gulf was known to be a significant sperm whaling ground for nineteenth-century Yankee whalers. 

All of the world's species of Stenella occur in the Gulf and many of them in fairly large numbers.  The pantropical spotted dolphin (S. attenuata) is the most common and abundant delphinid in oceanic waters deeper than 200 m (656 ft.).  The Atlantic spotted dolphin (S. frontalis) is a common offshore dolphin in waters from 20 to 200 m deep, with scattered records out to 1,000 m (3,281 ft.).  There are more Gulf records of these dolphins than for any other species of offshore cetacean, and it is the only species, other than the bottlenose dolphin, that commonly occurs over the continental shelf.  There are fewer records of the spinner dolphin (S. longirostris), which has a pantropical distribution, than for any other species of Stenella in the Gulf.  The Clymene dolphin (S. clymene) is an endemic of Atlantic tropical and subtropical waters that ranges primarily between the 100 m (328 ft.) and 2,000 m (6,562 ft.) depth contours.  The striped dolphin (S. coeruleoalba) is a deepwater species and occurs worldwide in tropical and warm temperate waters. 

Other delphinids thought to be rare based on stranding records actually appear to be common in deeper oceanic waters.  Rough-toothed dolphins (Steno bredanensis) rarely strand, but they have been sighted on many occasions throughout all seasons in the Gulf.  Melon-headed whales (Peponocephala electra) were first recorded on the basis of strandings in the past decade, but now they have been sighted numerous times in waters 200 to 2,000 m deep.  The Gulf has produced more sightings of Fraser's dolphin (Lagenodelphis hosei) than anywhere else in the Atlantic Ocean.  Sightings have been made in the northern Gulf in waters around 1,000 m deep.  There are numerous sightings of Risso's dolphin (Grampus griseus), which previously was thought to be rare in the Gulf, along the upper continental slope off Alabama, Mississippi, and eastern Louisiana.  

Editions of The Mammals of Texas published prior to 2004 included an account for the common dolphin, Delphinus delphis.  Common dolphins were recently split into two species, a short-beaked form (D. delphis) and a long-beaked form (D. capensis).  This edition, however, does not include an account for either species.  Although both stranding and sighting records exist for the Gulf, it now appears that earlier workers consistently misidentified other species, mainly Clymene dolphins (Stenella clymene), as common dolphins.  All museum skulls that were previously noted as Delphinus have been reidentified as either S. clymene or the pantropical spotted dolphin, S. attenuata.  This, there is no evidence that common dolphins occur in the Gulf of Mexico.  Because of their known distribution in similar latitudes in other places in the world, both common dolphin species may eventually be found in the Gulf, most likely in the southern waters that have not been surveyed adequately. 

Some of the larger whales that occur in the Gulf have been placed on the endangered species list by the US Fish and Wildlife Service (USFWS) in the Federal Register.  These include the North Atlantic right whale, sei whale, blue whale, fin whale, and humpback whale (see table 2).  The sperm whale also is listed as endangered, but recent information suggests that it is the most common large whale in the Gulf of Mexico. 

No dolphins or other odontocetes in the Gulf are considered endangered at the species level, but TPWD lists as threatened the pygmy sperm whale, dwarf sperm whale, Gervais's beaked whale, Cuvier's beaked whale, killer whale, false killer whale, pygmy killer whale, short-finned pilot whale, rough-toothed dolphin, and Atlantic spotted dolphin (see table 2).  There is really no basis for these listings other than rarity in the stranding record. 

 

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 (North Atlantic right whale).

3. Throat grooves end well before navel .................................... 4

Throat grooves extend to or beyond navel ................................. 5

4. Ventral grooves number 50-70, longest ending between flippers; 231-285 white or yellowish-white baleen plates per side, <21 cm long; conspicuous white bands on flippers; maximum body length 9 m.  Balaenoptera acutorostrata (common minke whale).

Ventral grooves number 32-60, longest ending well short of navel; 219-402 pairs of black baleen plates, <80 cm long; flippers totally dark; maximum body length 16 m.  Balaenoptera borealis (sei whale).

5. Flippers >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 <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 >20 m .................................... 7

Head with series of three parallel ridges from blowhole to snout; 40-50 ventral grooves; maximum body length <15 m.  Balaenoptera brydei (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 30 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 jaw about 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 <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 >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 <10.2% of total length; 8-11 (rarely up to 13) teeth in each side of lower jaw.  Kogia sima (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's 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 (one or two 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 <0.5 m in height; flippers long and pointed to slightly rounded at tips; body never >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 about 6-7 m long.  Globicephala macrorhynchus (short-finned pilot whale).

Dorsal fin located near midpoint of back; body typically <6 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 up to 6 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 <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 that 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. Flippers, flukes, and dorsal fin relatively small; broad dark stripe from eye to anus area; dorsal fin only slightly recurved; body stocky; extremely short but well-defined beak.  Lagenodelphis hosei (Fraser's dolphin).

Beak moderate to long (>3% of body length); appendages of normal dolphin proportions ........................................................................... 22

22. Body coloration dark gray on back, lighter gray on sides, with white to pink belly; no stripes or spots; beak relatively short and thick; 20-26 teeth present in each side of upper jaw and 18-24 teeth present in each side of lower jaw.  Tursiops truncatus (common bottlenose dolphin).

Body coloration includes numerous spots, mottling, or stripes; beak relatively long and slender; up to 200 total teeth present in mouth ............ 23

23. Body coloration heavily mottled with light or dark spots ........ 24

Body coloration without spots but traversed by one or more longitudinal stripes ........................................................................................... 25

24. 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).

25. Black stripes extending from eye to anus, from eye to flipper, and from above flipper toward belly; 43-50 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 mustache area; chin white to cream colored; tip of upper jaw to apex of melon <12 cm; seldom more than 46 teeth in each side of jaw.  Stenella clymene (Clymene dolphin).

Dark rostrum without mustache; tip of upper jaw to apex of melon >12 cm; chin gray to black; usually more than 46 teeth in each side of the jaw.  Stenella longirostris (spinner dolphin). 

 

SUBORDER MYSTICETI

BALEEN WHALES

Within the Gulf of Mexico, this suborder is represented by seven species arranged into two familes, the Balaenidae and the Balaenopteridae.

Family Balaenidae

RIGHT WHALES

This family, which includes three species, has the most extravagant baleen apparatus of all baleen whales.  The head is correspondingly enormous, in some species up to almost 40% of the body length; there are no throat and chest grooves, as in Balaenopteridae, and no dorsal fin.  The baleen plates are the longest in the Cetacea.  A single species of this family is known from the Gulf of Mexico, and it is of extralimital distribution in the region.

 

Family Balaenopteridae

RORQUALS OR BALEEN WHALES

This family comprises two genera and six species that occur in all oceans and adjoining seas of the world, with all six species having been recorded from the Gulf of Mexico.  The term "rorqual" is derived from the Norwegian words ror, for tube or groove, and qual, for whale.  These whales vary enormously in size, with head and body length of sexually mature adults 6.7-31 m and weights up to 160 metric tons.  In each species, the females are larger than the males of the same age.  All of these whales are characterized by longitudinal folds or pleats on the throat, chest, and in some species, the belly.  The furrows allow the throat to expand enormously and thus greatly increase the amount of material that the whale can take in when feeding.  The Balaenopteridae are distinguished from the Balaenidae by the presence of throat and chest furrows, a more elongated and streamlined body form with a relatively smaller head and more tapering pectoral fin, a softer and less massive tongue, and shorter and less flexible baleen.  They also have a small dorsal fin. 

 

SUBORDER ODONTOCETI

TOOTHED WHALES

The vast majority of marine mammals in the Gulf of Mexico are representatives of this suborder.  There are nine families and 68 species worldwide, of which four families and 24 species have been recorded from (or probably occur in) the Gulf of Mexico.  The Gulf representatives include a wide variety of toothed whales and dolphins, ranging in size from the large sperm whales (body length 15 m) to the small oceanic dolphins (body length 1.5-2.5 m).

Family Delphinidae

TOOTHED WHALES AND DOLPHINS

This is the most diverse family of cetaceans in the world, with a total of 17 genera and 33 species.  It includes all of the classic dolphins, those smaller cetaceans with beaklike snouts and slender, streamlined bodies.  Head and body length of delphinids in the Gulf of Mexico range from as little as 1.8 m in species of Stenella to as much as 9.8 m in Orcinus; weight in fully grown individuals ranges from about 50 to 10,000 kg.  The blowhole is located well back from the tip of the beak or the front of the head.  The pectoral and dorsal fins are falcate, triangular, or broadly rounded, and the dorsal fin is near the middle of the back.  The Delphinidae include the most agile and some of the speediest cetaceans.  They commonly surface several times a minute and frequently leap clear of the water. 

 

Family Kogiidae

PYGMY AND DWARF SPERM WHALES

This family includes two species of the genus Kogia, both of which are uncommon in the Gulf of Mexico.  The facial part of the skull in these whales is among the shortest in cetaceans.  These whales resemble the sperm whale (Physeter macrocephalus) by having a spermaceti organ in the head and functional teeth confined to the lower jaw.  That is why the pygmy and dwarf sperm whales were typically combined into a single family with Physeter.  Both species of Kogia, however, have blowholes situated on top of the head instead of at the end of the snout and a distinct, curved dorsal fin; Physeter has no true dorsal fin.  Thus, the pygmy and dwarf sperm whales are now regarded as members of the family Kogiidae.  

 

Family Physeteridae

SPERM WHALE

This family includes a single species, the sperm whale, which occurs in all oceans and adjoining seas of the world, except in polar ice fields.  This is the largest toothed mammal in the world and the most sexually dimorphic of all cetaceans.  The most striking morphological feature is the huge spermaceti organ in the head, filled with up to 1,900 liters of waxy oil.  The sperm whale is by far the most common large whale in the Gulf of Mexico. 

 

Family Ziphiidae

BEAKED WHALES

This family comprises five genera and 19 species, which occur in all the oceans and adjoining seas of the world.  The vernacular name is derived from the long, narrow beak that forms a continuous smooth profile with the head in all forms known from the Gulf of Mexico.  In most ziphiids, the teeth show strong sexual dimorphism, with males having one pair of unusually large teeth in the lower jaw; in females, the teeth are absent or vestigial.  The cetacean fauna of the Gulf includes two genera and four species of beaked whales that are among the least known of cetaceans in these waters.  They usually remain well out to sea, avoid ships, and dive to great depths to secure cephalopods and fish.  The taxonomy of beaked whales is presently being revised; with analysis of newly discovered skull fragments and recently acquired genetic samples, it is likely that several new species will be described in the next several years. 

 

 

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.