Rice's whale (''Balaenoptera ricei''), also known as the Gulf of Mexico whale, is a
species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
of
baleen whale
Baleen whales ( systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea ( whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in th ...
endemic to the northern
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...
. Initially identified as a
subpopulation
In statistics, a population is a set of similar items or events which is of interest for some question or experiment. A statistical population can be a group of existing objects (e.g. the set of all stars within the Milky Way galaxy) or a hypot ...
of the
Bryde's whale,
genetic
Genetic may refer to:
*Genetics, in biology, the science of genes, heredity, and the variation of organisms
**Genetic, used as an adjective, refers to genes
***Genetic disorder, any disorder caused by a genetic mutation, whether inherited or de nov ...
and skeletal studies found it to be a distinct species by 2021. In outward appearance, it is virtually identical to the Bryde's whale. Its body is streamlined and sleek, with a uniformly
dark charcoal gray dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
* Dorsal co ...
and pale to pinkish underside. A diagnostic feature often used by
field scientists to distinguish Rice's whales from whales other than the Bryde's whale is the three prominent ridges that line the top of its head. The species can be distinguished from the Bryde's whale by the shape of the
nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose.
Ea ...
s, which have wider gaps due to a unique wrapping by the
frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, pa ...
s, its unique vocal repertoire, and genetic differences.
It is a medium-sized baleen whale that grows up to in length and weighs up to . The Rice's whale inhabits a restricted stretch along the
continental slope
A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...
in the northeastern part of the Gulf of Mexico between depths of off the coast of western
Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...
, although some whales have been sighted in the northwestern portions and the species may have inhabited a wider
distribution Distribution may refer to:
Mathematics
*Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations
*Probability distribution, the probability of a particular value or value range of a varia ...
throughout the Gulf in historical times. It does not migrate but remains within this area year-round. Little is known about the feeding behavior of Rice's whales, but data from a tagged individual revealed a
diel vertical diving pattern, in which the whale spends most of the day feeding at or near the seafloor at depths of up to and night at the surface. The whale's diet remains unknown, but
lanternfish
Lanternfishes (or myctophids, from the Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented ...
and
hatchetfish are suspected prey.
The Rice's whale is on the brink of
extinction
Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...
and is alongside the
vaquita
The vaquita ( ; ''Phocoena sinus'') is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Averaging (females) or (males) in length, it is the smallest of all living cetaceans. The species i ...
as one of the most
endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...
cetaceans in the world. It is listed as
critically endangered in the
IUCN Red List
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
and protected under the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...
Endangered Species Act
The Endangered Species Act of 1973 (ESA or "The Act"; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of e ...
. The best population estimate is 33, with as little as 16 mature individuals, and the population is continuing to decline. The reasons why the species' population declined to its current state remains poorly understood, but scientists believe that the
industrialization
Industrialisation ( alternatively spelled industrialization) is the period of social and economic change that transforms a human group from an agrarian society into an industrial society. This involves an extensive re-organisation of an econ ...
of the Gulf of Mexico and the increase of
anthropogenic activities within its habitat are primary contributors; unlike most baleen whales it is unlikely that
whaling
Whaling is the process of hunting of whales for their usable products such as meat and blubber, which can be turned into a type of oil that became increasingly important in the Industrial Revolution.
It was practiced as an organized industry ...
had an impact. Today, the Rice's whale's main threats are related to industrial and commercial activities within its habitat, including
oil pollution
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...
, ship collisions, and underwater noise from
seismic surveys
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning " earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through o ...
and vessel traffic. It has also shown to be especially vulnerable to local catastrophic events such as the 2010
''Deepwater Horizon'' oil spill, which single-handedly killed nearly twenty percent of the species' population.
Taxonomy
Discovery and naming

The Rice's whale was likely first documented by the
Yankee whaling ship ''Keziah'' in 1790, which reported the chasing of a "finback" in the
Bay of Campeche
The Bay of Campeche ( es, Bahía de Campeche), or Campeche Sound, is a bight in the southern area of the Gulf of Mexico, forming the north side of the Isthmus of Tehuantepec. It is surrounded on three sides by the Mexican states of Campeche, Tab ...
. At least 49 additional encounters of "finbacks" were reported throughout the
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...
during the 18th and 19th centuries.
Scientists generally agree that the "finbacks" were most likely Rice's whales, as the
species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
is the only baleen whale that resides in the Gulf year-round.
[ ] While
fin whale
The fin whale (''Balaenoptera physalus''), also known as finback whale or common rorqual and formerly known as herring whale or razorback whale, is a cetacean belonging to the parvorder of baleen whales. It is the second-longest species of c ...
s (of which the name "finback" applies to today),
blue whale
The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can b ...
s,
sei whale
The sei whale ( , ; ''Balaenoptera borealis'') is a baleen whale, the third-largest rorqual after the blue whale and the fin whale. It inhabits most oceans and adjoining seas, and prefers deep offshore waters. It avoids polar and tropical ...
s, and
common minke whale
The common minke whale or northern minke whale (''Balaenoptera acutorostrata'') is a species of minke whale within the suborder of baleen whales.
It is the smallest species of the rorquals and the second smallest species of baleen whale. Althoug ...
s have been sighted in the Gulf of Mexico, their presence is extralimital and they only appear in the area as occasional wanderers.
The Rice's whale was first scientifically recognized by late
cetologist Dale Rice in 1965, but as a local population of the closely related
Bryde's whale.
The extent of its modern geographic isolation was uncovered during the 1990s.
During the 20th and early 21st centuries, this group of supposed Bryde's whales was vernacularly referred to as the "Gulf of Mexico whale."
A 2014
mitochondrial
A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...
and
nuclear DNA
Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. ...
study by Rosel and Wilcox discovered that the Gulf of Mexico whales belong to a genetically distinct lineage that does not belong to either of the two members of the Bryde's whale complex (''B. edeni brydei'' and ''B. edeni edeni''), demonstrating that they may be a new
subspecies or species.
However, the study refrained from describing a new taxon, which requires a then-absent
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...
specimen to erect.
The taxonomic situation remained unchanged until 2019 when a dead individual washed up at
Everglades National Park
Everglades National Park is an American national park that protects the southern twenty percent of the original Everglades in Florida. The park is the largest tropical wilderness in the United States and the largest wilderness of any kind east ...
in
Florida
Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, a ...
, providing the needed holotype without having to kill or harm any living members of the critically endangered population.
This specimen was buried to decompose into a skeleton, exhumed, and transported to the
Smithsonian Institution
The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...
, where it is now cataloged as USNM 594665. In a 2021 taxonomic study, Rosel, Wilcox, and colleagues demonstrated through USNM 594665 that the Gulf of Mexico whale is also morphologically distinct from the Bryde's whale, thus confirming its identity as a new species. The subsequent scientific name ''Balaenoptera ricei'' and common name Rice's whale honor Rice for his role in discovering the whales' existence and to commemorate his 60-year contributions to marine mammal science. The study also commented that the naming was done to complement the trend of naming members of the Bryde's whale complex after people.
However, some scientists maintain the use of "Gulf of Mexico whale" as the preferred common name. A 2022 letter by Peter Corkeron of
New England Aquarium
The New England Aquarium is a public aquarium located in Boston, Massachusetts. The species exhibited include harbor and northern fur seals, California sea lions, African and southern rockhopper penguins, giant Pacific octopuses, weedy seadr ...
and colleagues argued that most baleen whales have common names based on their geographic origin (with exceptions typically for wide-ranging species), that specifying a geographic origin encourages greater awareness of the species' endangered status, that the trend of Bryde's whale complex members having names honoring people is inconsistent (i.e. the sei whale's common name references a fish and scientific name a geographic region), and that promoting such perceived trend risks glorifying problematic namesakes (i.e. Eden's whale honors
Ashley Eden
Sir Ashley Eden (13 November 1831 – 8 July 1887) was an official and diplomat in British India.
Background and education
Eden was born at Hertingfordbury, Hertfordshire, the third son of Robert Eden, 3rd Baron Auckland, Bishop of Bath ...
, a colonial officer of
British India
The provinces of India, earlier presidencies of British India and still earlier, presidency towns, were the administrative divisions of British governance on the Indian subcontinent. Collectively, they have been called British India. In one ...
).
Rosel and colleagues published a response letter in the same journal issue presenting counterarguments, namely that "Gulf of Mexico whale" is too ambiguous and may be confused with other local cetaceans, that a region-specific name alienates outsiders and risks reducing global interest, and that encouraging an alternate common name when "Rice's whale" is already widely used will increase confusion.
Phylogeny
The Rice's whale is a type of "Bryde's-like whale," a group of
rorqual
Rorquals () are the largest group of baleen whales, which comprise the family Balaenopteridae, containing ten extant species in three genera. They include the largest animal that has ever lived, the blue whale, which can reach , and the fin ...
s within the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...
''
Balaenoptera
''Balaenoptera'' () is a genus of rorquals containing eight extant species. ''Balaenoptera'' comprises all but two of the extant species in its family (the humpback whale and gray whale); the genus is currently polyphyletic, with the two aforemen ...
'' that are distinct genetically and in skeletal morphology but are near-indistinguishable in outward appearance. Other members of this group include the Bryde's whale (''B. brydei''), Eden's whale (''B. edeni''), and
Omura's whale
Omura's whale or the dwarf fin whale (''Balaenoptera omurai'') is a species of rorqual about which very little is known. Before its formal description, it was referred to as a small, dwarf or pygmy form of Bryde's whale by various sources. The ...
(''B. omurai''). However, Rosel et al. (2021) commented that the term may no longer be necessary.
The following cladogram is modified from a
phylogenetic tree constructed by Rosel et al. (2021) based on mitochondrial DNA. Based on the study, the Rice's whale's closest living relative is the Eden's whale. The two form a clade that forms a
polytomy
An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
with the sei whale and Bryde's whale.
Description

It is an intermediate-sized rorqual that is usually about the same size as the Eden's whale, although few adults have been reliably measured to date. The largest measured individual was a
lactating
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process naturally occurs with all sexually mature female mammals, although it may predate mammals. The proces ...
female in length; USNM 594665 is the largest known male of the species and is long. Adults may be as small as in length, and many verified and possible Rice's whales do not exceed . One beached calf was measured at in length. In the wild, another calf has been observed to be around half the length of its supposed parent. One whale that washed up in
Louisiana
Louisiana , group=pronunciation (French: ''La Louisiane'') is a U.S. state, state in the Deep South and South Central United States, South Central regions of the United States. It is the List of U.S. states and territories by area, 20th-smal ...
in 1982 was estimated at , but whether this is a Rice's whale remains unconfirmed as information on the diagnostic rostral ridges was never documented.
When using a length-weight function developed by Ohsumi (1980), a length would correspond to a mass of around .
However, the
NOAA
The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...
reports a maximum weight of .
Appearance and coloring

In external appearance, the Rice's whale and Bryde's whale are virtually identical
and when compared can only be conclusively distinguished by their genetics, skeletal anatomy, and acoustic signatures. Like the Bryde's whale, the body shape is streamlined and sleek. The dorsal fin is shaped like a large hook that can range between ~ tall in adults and located around two-thirds of the length back from the snout. The smooth-edged tail flukes can be up to in width. The flat and somewhat pointed
rostrum
Rostrum may refer to:
* Any kind of a platform for a speaker:
**dais
**pulpit
* Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects
* Rostrum (ship), a form of bow on naval ships
* Ros ...
(top of the head) shows three prominent ridges: a large ridge along the center and two smaller ridges on the left and right sides. This unique trait only appears in Rice's whales and members of the Bryde's whale complex, making it a diagnostic feature when
whale watching
Whale watching is the practice of observing whales and dolphins (cetaceans) in their natural habitat. Whale watching is mostly a recreational activity (cf. birdwatching), but it can also serve scientific and/or educational purposes.Hoyt, E. 20 ...
.
The
dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
* Dorsal co ...
side of the body is uniformly
dark charcoal gray,
although this is sometimes reported as dark brown.
The belly and underside of the tail is pale to pinkish. This light coloring is especially prominent on the
ventral
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
side of the
peduncle Peduncle may refer to:
*Peduncle (botany), a stalk supporting an inflorescence, which is the part of the shoot of seed plants where flowers are formed
*Peduncle (anatomy), a stem, through which a mass of tissue is attached to a body
**Peduncle (art ...
. There is neither asymmetric pigmentation on the lower jaws nor blaze or chevron pattering on the body, which distinguishes the Rice's whale from fin whales and Omura's whales. The flippers are uniformly dark-colored. In some
phenotypic variations, a gradient of white also appears around the rim of the dorsal fin and/or along the side of the body, but there is no consistency of the trait between individual whales.
Forty-four to 54 ventral pleats run down the underside of the mouth, which are
creases that allows the whale to expand the inside of its mouth when feeding. The pleats usually reach up to the
navel
The navel (clinically known as the umbilicus, commonly known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All placental mammals have a navel, altho ...
, but some pleats extend beyond it. In the holotype specimen, one pleat extended beyond the navel and two additional elongated pleats were observed, although they could not be measured.
Skeleton
Knowledge of the skeletal anatomy is largely inferred from the holotype. However, it is not the only skeletal remains of Rice's whales accessible to science. Rosel et al. (2021) listed three additional specimens that were recovered in earlier years. The first is a skull (LSUMZ 17027) that was discovered in the
Chandeleur Islands
The Chandeleur Islands (french: Îles Chandeleur) are a chain of uninhabited barrier islands approximately long, located in the Gulf of Mexico, marking the outer boundary of the Chandeleur Sound. They form the easternmost point of the state of L ...
, Louisiana in 1954, which was initially identified as a fin whale but later genetically confirmed to be a Rice's whale. However, the skull is incomplete. The second is a complete skeleton (USNM 572922) recovered from a long subadult that washed up in
North Carolina
North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia a ...
in 2003. The third is the skeleton (UF33536) of the long lactating female, which washed up in
Tampa Bay
Tampa Bay is a large natural harbor and shallow estuary connected to the Gulf of Mexico on the west-central coast of Florida, comprising Hillsborough Bay, McKay Bay, Old Tampa Bay, Middle Tampa Bay, and Lower Tampa Bay. The largest freshwater ...
, Florida in 2009 and was subsequently disposed of via burial at a
nearby park.
Prior to the stranding of USNM 594665, this was considered a candidate specimen to serve as the Rice's whale holotype, but upon its excavation in 2018 it was found that the skull was crushed and much of the skeleton corroded as tides submerged it in water over the nine years it was buried.
Skull

The holotype skull is long, making up a little over one-fourth of the total body length, and wide. The upper jaw is in total length and wide at the antorbital notch (the point before the
maxillary bone
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
expands to connect with the rest of the skull).
The skull morphology between Rice's whales and Bryde's whale diverge in the nasals and adjacent bones, which are the primary diagnostic features defined by Rosel et al. (2021) that morphologically distinguishes between the two species. In the Rice's whale, the
frontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, pa ...
s uniquely wrap around the posterior tips of triangular
nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose.
Ea ...
s and extend down in between them, which opens a larger gap compared to Bryde's whale and Eden's whale and does not narrow posteriorly. The Rice's whale can also be distinguished from the Eden's whale by the narrow exposure of the frontals between the maxilla's ascending processes and
supraoccipital
The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cere ...
, and from the Omura's whale by how the premaxilla extends to the frontals.
Like all baleen whales, the jawlines of the skull are lined with bristles of
baleen
Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and ...
instead of teeth. In Rice's whales, the fringes of these plates throughout the jawline and all baleen in the anterior jaw positions are uniformly cream in color, which darken into black in the posterior positions above the fringe. The number of plates per jawline is variable and may between 230 to 290 plates. The length of the largest plate can range between .
Postcranial
There are fifty-three vertebrae in the spinal column.
This is slightly fewer than in relatives like the sei whale and Bryde's whale, which have 56-57 and 54-55 vertebrae respectively.
The vertebral formula is: seven
cervical vertebrae
In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...
in the neck, thirteen
thoracic vertebrae
In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
in the upper back, thirteen
lumbar vertebrae
The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse ...
in the lower back, and twenty
caudal vertebrae
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
in the tail. Thirteen pairs of ribs connect each thoracic vertebrae, with the head of each first rib bifurcating into two ends. There are a few unique features in the postcranial skeleton. The
stylohyal bone, the largest component of the
hyoid apparatus
The hyoid apparatus is the collective term used in veterinary anatomy for the bones which suspend the tongue and larynx. It consists of pairs of stylohyoid, thyrohyoid, epihyoid and ceratohyoid bones, and a single basihyoid bone. The hyoid appar ...
that stabilizes the
larynx,
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its ...
, and
tongue
The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste bu ...
, is broad and exhibits little curvature. This contrasts with the stylohyal bones in Bryde's whales, which have a degree of curvature and are longer than wide. In the
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
hip, the
pelvic bones
The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, isc ...
are nearly straight, with only one side having a tiny projection.
Range and habitat
The Rice's whale is mainly restricted to the northeastern Gulf of Mexico. Specifically, scientists identified its core habitat range as a small stretch along the
continental slope
A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental marg ...
between depths of within and near the
De Soto Canyon off the coasts of western Florida,
Alabama
(We dare defend our rights)
, anthem = " Alabama"
, image_map = Alabama in United States.svg
, seat = Montgomery
, LargestCity = Huntsville
, LargestCounty = Baldwin County
, LargestMetro = Greater Birmingham
, area_total_km2 = 135,7 ...
, and eastern Louisiana. It is a non-
migratory
Migration, migratory, or migrate may refer to: Human migration
* Human migration, physical movement by humans from one region to another
** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
species and usually stays within this area year-round, making it the only known baleen whale resident to the Gulf of Mexico.
A female that was
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
-tagged for 33 days in 2010 revealed that the whale spent 87.5% of the month within a range just north of the De Soto Canyon, leaving only for a single 6-day round-trip to an area southeast. The reason as to why the Rice's whale restricts itself to such a small habitat range remains unknown.
There were a few live sightings in the western Gulf outside the core habitat, including one sighted off the coast of Texas that was genetically confirmed as a Rice's whale via
biopsy
A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a d ...
. Acoustic surveys off western Louisiana in 2019 also detected Rice's whale calls. These observations occurred on the continental slope at similar depth ranges to the core habitat. There is little evidence that these are attempts in regularly inhabiting western waters, though they may contain a marginal habitat zone.
Whaling logbooks during the 18th and 19th centuries document at least 50 occurrences of "finbacks" (likely Rice's whales) distributed throughout the Gulf of Mexico, suggesting that the species once had had a wider historical distribution. These encounters concentrated near the continental slopes south of the
Mississippi River Basin
The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
, in the Bay of Campeche, and north of the
Yucatán Peninsula
The Yucatán Peninsula (, also , ; es, Península de Yucatán ) is a large peninsula in southeastern Mexico and adjacent portions of Belize and Guatemala. The peninsula extends towards the northeast, separating the Gulf of Mexico to the north ...
and occurred at a wider depth range, including some at depths greater than .
It is still unknown why the Rice's whale's distribution has declined to its current state,
but the NOAA considers increased
industrialization
Industrialisation ( alternatively spelled industrialization) is the period of social and economic change that transforms a human group from an agrarian society into an industrial society. This involves an extensive re-organisation of an econ ...
throughout the Gulf of Mexico and the subsequent
underwater noise it brought a likely major factor. It is unlikely that whaling was another major factor, as the species did not recover from supposed whaling mortalities as seen in cetaceans that have been hunted in the past despite local whaling having been defunct for over a century ago, and there are no recorded kill counts.
While the distribution within the American
exclusive economic zone in the northern half of the Gulf has been extensively surveyed, the southern
Mexican
Mexican may refer to:
Mexico and its culture
*Being related to, from, or connected to the country of Mexico, in North America
** People
*** Mexicans, inhabitants of the country Mexico and their descendants
*** Mexica, ancient indigenous people ...
half remains poorly studied, and there remains a possibility that a previously undetected population of Rice's whale might exist there. Opportunistic visual surveys have been conducted between 1997 and 1999 during a series of six oceanographic surveys within the Bay of Campeche and
Yucatán Channel
The Yucatán Channel or Straits of Yucatán ( Spanish: ''Canal de Yucatán'') is a strait between Mexico and Cuba. It connects the Yucatán Basin of the Caribbean Sea with the Gulf of Mexico. It is just over wide and nearly deep at its deepest ...
. Only one unidentified rorqual was sighted. However, these efforts did not survey other potential habitat locations such as the continental slope north of the
Campeche Bank
Campeche Bank is part of the Gulf of Mexico and extends from the Yucatan Straits in the east to the Tabasco-Campeche Basin in the west. Campeche Bankin Geonames.org (cc-by)/ref> The Campeche ocean bank is from Mexico's geography of Campeche na ...
, where a number of historical Rice's whales were recorded. A compilation of recent isolated cetacean encounters in the Mexican Gulf collected by Ortega-Ortiz in 2002 found no records of potential Rice's whales.
Several standings from the Atlantic Ocean have been documented, including whales along eastern Florida,
Georgia
Georgia most commonly refers to:
* Georgia (country), a country in the Caucasus region of Eurasia
* Georgia (U.S. state), a state in the Southeast United States
Georgia may also refer to:
Places
Historical states and entities
* Related to t ...
, the
Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
in
Virginia
Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the East Coast of the United States, Atlantic Coast and the Appalachian Mountains. The geography an ...
, and two genetically confirmed cases from North Carolina and
South Carolina
)'' Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no)
, anthem = "Carolina";" South Carolina On My Mind"
, Former = Province of South Carolina
, seat = Columbia
, LargestCity = Charleston
, LargestMetro = G ...
. The genetically unconfirmed cases are usually referred to as simply Bryde's-like whales due to the inability to visually differentiate between the Rice's whale and Bryde's whale, which is present in deeper Atlantic waters. There are no confirmed live sightings of Rice's whales in the Atlantic; five recorded observations of Bryde's-like whales during survey efforts in the 1990s in the area are most likely either Bryde's whales or sei whales as they were sighted in waters deeper than , far from the known range of the Rice's whale. In addition, acoustic studies off
Jacksonville, Florida
Jacksonville is a city located on the Atlantic coast of northeast Florida, the most populous city proper in the state and is the List of United States cities by area, largest city by area in the contiguous United States as of 2020. It is the co ...
and
Cherry Point, North Carolina
Marine Corps Air Station Cherry Point or MCAS Cherry Point (*) is a United States Marine Corps airfield located in Havelock, North Carolina, United States, in the eastern part of the state. It was built in 1941, and was commissioned in 1942 and ...
were unable to detect Rice's whale calls. It is therefore evident that Rice's whales are at best extremely rare in Atlantic waters. James G. Mead of the
International Whaling Commission
The International Whaling Commission (IWC) is a specialised regional fishery management organisation, established under the terms of the 1946 International Convention for the Regulation of Whaling (ICRW) to "provide for the proper conservation ...
suggested that the stranded records are most likely strays that wandered from the Gulf of Mexico.
Ecology and behavior
Feeding and diving behavior

Little is known about the feeding ecology of Rice's whales, but it differs from the feeding behavior of Bryde's whales. Bryde's whales typically feed on a variety of pelagic prey such as schooling fish like
anchovies
An anchovy is a small, common forage fish of the family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water.
More than 140 species are placed in 1 ...
,
sardine
"Sardine" and "pilchard" are common names for various species of small, oily forage fish in the herring family Clupeidae. The term "sardine" was first used in English during the early 15th century, a folk etymology says it comes from the ...
s,
menhaden
Menhaden, also known as mossbunker and bunker and "the most important fish in the sea", are forage fish of the genera ''Brevoortia'' and ''Ethmidium'', two genera of marine fish in the family Clupeidae. ''Menhaden'' is a blend of ''poghaden'' ...
, and
herring
Herring are forage fish, mostly belonging to the family of Clupeidae.
Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Ocea ...
,
copepod
Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...
s,
krill
Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian word ', meaning "small fry of fish", which is also often attributed to species of fish.
Krill are consid ...
, and
salps
A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...
near the surface, but surface feeding has never been observed in Rice's whales.
In 2015, scientists tagged a Rice's whale, which provided nearly 3 days (63.85 hours) worth of information about the diving behavior of the animal. It revealed that the Rice's whale had a
diel vertical diving pattern, spending its day in deep water and night near the surface. During daytime hours, the whale spent most of its time diving at depths of up to below the surface, likely at or nearby the seafloor. A total of 119 daytime deep dives were recorded, with only 43% of the daytime spent within of the surface.
Lunge feeding
Aquatic feeding mechanisms face a special difficulty as compared to feeding on land, because the density of water is about the same as that of the prey, so the prey tends to be pushed away when the mouth is closed. This problem was first identifi ...
was detected during the deepest parts of the dives, which indicates the Rice's whale was feeding at or just above the seafloor.
What exactly it was feeding on remains a mystery, but
lanternfish
Lanternfishes (or myctophids, from the Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented ...
and
hatchetfish are common in these areas, so it is possible that they are part of the Rice's whale diet.
During nighttime hours, the whale spent 88% of its time within of the surface, with occasional dives between below the surface. Three of the deepest dives, which were between below the surface, took place just before sunrise or just after sunset.
GPS data from the 2010 tagged individual found that the whale swam at an average sustained speed, the speed at which the animal travels without tiring, of when staying within a specific location, and when traveling over long distances. The fastest sustained speed recorded was .
Vocalization
The whale may exhibit a unique vocal repertoire that differs from the acoustic signatures of Bryde's whales or any other known baleen whale, making vocalization a potential diagnostic feature. Five call types are known for wild Rice's whale, although only three of them have been definitively linked to the species.
Two additional call types have also been documented from a captive juvenile.
Each individual makes around 22 calls per day, with each call producing on average 8.2 sounds per hour.
Long-moans are the most common call types. They usually last between 20–27 seconds at a frequency range between 43-208
Hz and exhibit a regular pattern of
amplitude modulation with a modulation frequency of 3.4 Hz. In occasional association with long-moans are tonal-sequences, which consists of a series of narrow-
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
tonals that each have an average duration of 3.6 seconds at a frequency range of 99.4-107.4 Hz. The tonal-sequences can contain up to 6 different tonals. The occurrence of tonal-sequences after long-moans are relatively rare; only 3.2% of documented long-moans are followed by tonal-sequences with a mean time gap of 3.87 seconds. A last set of call types are the downsweeps, brief sounds characterized by a sharp drop in frequency from beginning to end.
In the Rice's whale, there are multiple documented variations of downsweeps. The first variation is the downsweep-sequence that occurs in repetition; sequences range between 2 to 27 downsweeps with an average of 0.8 seconds between each downsweep. Each individual downsweep usually lasts 0.3 seconds with frequencies beginning at 113 Hz and ending at 51 Hz.
Another variation consists of "pulse pairs" of downswept pulses that start with a start-end frequency range of 143–78 Hz with individual pulses and interpulse intervals ranging between 0.4-0.7 seconds and 0.6-1.3 seconds respectively. A third possible variation consists of a three-segment sequence of downsweeps that occur at higher frequencies of 170–110 Hz. Each segment may include single downsweep, doublets, or triplets.
Of these five documented call types, only the long-moans, downsweep-sequences, and pulse pairs have been definitively linked with individual whales.
The other two documented types have yet to be verified in the same manner, but scientists generally agree that they belong to the Rice's whale through
parsimony
Parsimony refers to the quality of economy or frugality in the use of resources.
Parsimony may also refer to
* The Law of Parsimony, or Occam's razor, a problem-solving principle
** Maximum parsimony (phylogenetics), an optimality criterion in p ...
.
In November 1988, a stranded female was rescued and treated in captivity at
SeaWorld Orlando
SeaWorld Orlando is a theme park and marine zoological park, in Orlando, Florida. It is owned and operated by SeaWorld Parks & Entertainment. When combined with its neighbor Discovery Cove and Aquatica, it forms SeaWorld Parks and Resorts Orla ...
until her release in January 1989. This whale was juvenile estimated to be around 1–2 years old. While in captivity, her acoustic signatures were monitored, and two types of calls were documented. The first was a growl-like pulsed moan that lasted between 0.5–51 seconds at a rate of 20-70 pulses per second with a frequency range of 200–900 Hz. They were first detected during late December and occurred periodically in the absence of humans in the tank, stopping only when the tank's surface sprinkler system was turned off in preparation for feeding or repair. The second was a sequence of discrete pulses lasting 10 milliseconds each at a frequency range of 400–600 Hz with intervals of 50-130 milliseconds between each pulse. They were rare, but sometimes occurred immediately before, after, or in-between a moan. These call types are unique among Rice's whales, but they may be due to the special circumstances of the captive juvenile. It is possible that the growl-like moans may be related to distress, as similar types of sounds have been documented in other baleen whales when disturbed or in agony. Based on vocal patterns of terrestrial mammals, the moans may also be related to isolation. It is also possible that the two documented call types may be related to age, and that the captive juvenile was intermediate between those of adults and calves. When vocalizing, the whale lowered her head slightly and blew bubbles from her right
blowhole
Blowhole may refer to:
* Blowhole (anatomy), the hole at the top of a whale's or other cetacean's head
*Blowhole (geology), a hole at the inland end of a sea cave
**Kiama Blowhole in Kiama, Australia
**The Blow Hole, a marine passage between Minst ...
. Because this was the only other time it opened, the other when breathing in which both blowholes opened, it is possible that the right blowhole may have had a function with vocalization, specifically the growl-like moans. However, alternative explanations such as illness or behavioral display could not be discounted.
Predation

There are no known observations of predation on Rice's whales, but it is likely that its main predator is the
killer whale
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus '' Orcinus'' and is recognizable by its black-and-white ...
, which is known in the Gulf of Mexico, as they have been seen attacking local
sperm whales
The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus '' Physeter'' and one of three extant species in the sperm whale famil ...
and
dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (t ...
s and are the only known natural predator of the Bryde's whale. There is debated speculation that some baleen whales migrate as an anti-predator adaptation, but the Rice's whale is a non-migratory species that clearly lacks this trait. A known common defensive behavior of rorquals is to flee upon encounter by killer whales, although this would be less effective when a calf is needed to be protected. Killer whales have also been observed to efficiently kill calves within minutes to hours in such a scenario. Given the likely low reproductive rate of Rice's whales due to their small numbers, the species would be especially vulnerable to such predation if it exists, although its rarity makes the chance of observing predation extremely low. The hunting of only a few calves or mothers can be sufficient enough to drive the population into a predator pit, a situation where the population is trapped in indefinitely low numbers due to predation.
Another potential predator may be the
great white shark
The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocean ...
, which is known to hunt
North Atlantic right whale
The North Atlantic right whale (''Eubalaena glacialis'') is a baleen whale, one of three right whale species belonging to the genus '' Eubalaena'', all of which were formerly classified as a single species. Because of their docile nature, their ...
calves in nursery waters off the coast of Florida and Georgia. In addition, it is a common scavenger of Bryde's whale carcasses elsewhere in the world. Like killer whales, however, there is no direct proof that great whites hunt Rice's whales.
Conservation status
The Rice's whale is on the brink of
extinction
Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...
and is one of the most
endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...
cetaceans in the world alongside the
vaquita
The vaquita ( ; ''Phocoena sinus'') is a species of porpoise endemic to the northern end of the Gulf of California in Baja California, Mexico. Averaging (females) or (males) in length, it is the smallest of all living cetaceans. The species i ...
.
Prior to its 2021 description as a distinct species, it was assessed as a
subpopulation
In statistics, a population is a set of similar items or events which is of interest for some question or experiment. A statistical population can be a group of existing objects (e.g. the set of all stars within the Milky Way galaxy) or a hypot ...
of the Bryde's whale. The Rice's whale is listed as
critically endangered in the
IUCN Red List
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
.
It is not individually listed in the
, but the Bryde's whale is listed in Appendix I.
The U.S. government also lists the Rice's whale as endangered under the
Endangered Species Act
The Endangered Species Act of 1973 (ESA or "The Act"; 16 U.S.C. § 1531 et seq.) is the primary law in the United States for protecting imperiled species. Designed to protect critically imperiled species from extinction as a "consequence of e ...
, thus banning all activities that may directly harm the species within American waters. However, the designation of a
critical habitat
Critical habitat is a habitat area essential to the conservation of a listed species, though the area need not actually be occupied by the species at the time it is designated. This is a specific term and designation within the U.S. Endangered Sp ...
as mandated under the Act has yet to occur, as information on the habitat ecology remains insufficient.
Population
Both male and female Rice's whales remain and breed within the Gulf of Mexico, contrasting with coexisting local sperm whales that see males wander outside and breed with females from other locations.
The Rice's whale sex ratio is somewhat close to 50:50; examinations of 32 whales identified 18 females and 14 males.
Individuals are usually seen alone or in pairs but have occasionally been sighted forming larger loose groups that are believed to be associated with feeding.
Population estimates are below 100 individuals and 50 mature individuals.
Multiple population studies of the species have been conducted since 1991, but due to the difficulty in surveying Rice's whales they are largely based on models and reliable exact figures are difficult to determine. Most models are statistically imprecise, having high
coefficients of variation (>CV 0.4). They are also restricted to within the northern Gulf and do not take into account the possible existence of Rice's whales in the southern half.
The best estimate to date is 33 individuals (CV 1.07) per a 2009 survey.
Studies in prior years have approximated abundances throughout the entire northern Gulf of Mexico ranging from 15 to 44 individuals (CV 0.61-1.1). Separate estimates exclusive to the northwestern Gulf have produced figures ranging between 0 to 3 individuals (CV 0.81-1.08).
These estimates are not comparable to each other through time differences as different variables were applied to each study such as the inclusion or exclusion of habitat
stratification.
A 2015 study by Roberts and colleagues
produced a larger estimate of 44 whales based on a habitat modeling technique that integrates survey data between 1994-2009.
This study had the lowest coefficient of variation (CV 0.27),
but its estimate aggregated over time.
In the same year, a research team commissioned by the
U.S. Fish and Wildlife Service
The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...
produced an estimate of 26 individuals (CV 0.4) when specifically accounting for damage caused by the
''Deepwater Horizon'' oil spill using 2003-2009 survey data and different geographic borders than the 2009 estimate.
More recently, a 2016 status report for the Endangered Species Act estimated the number of remaining mature individuals at 16, while the 2017 edition of the IUCN Red List puts this at 17 with the general population trend continuing to decrease.
Due to its extremely low population, the Rice's whale also faces the threat of
inbreeding depression
Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding (the breeding of related individuals). Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. ...
, which consequentially severely weakens the remaining population's ability to recover and survive due to the reduction of genetic diversity and accumulation of harmful
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...
s. To assess how well a population can survive on its own in the wild, geneticists employ the
50/500 rule, where the threshold for a population to successfully combat inbreeding depression is 50 individuals and to reduce mutation-creating
genetic drift
Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Genetic drift may cause gene variants to disappear completely and there ...
is 500 individuals. Because the Rice's whale's mature population is far below these thresholds, additional ecological traits such as a
k-seletected reproduction strategy slows the chance of recovery even further and puts the species at a high chance of entering a phenomenon known as an
extinction vortex
Extinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. This model shows the events that ultimately ...
. It has been projected that an assumed population of 35 Rice's whales would take 68 years to recover to 500 individuals. During this period, the species is more vulnerable to catastrophic events that can further damage the population's recovery chances. Such catastrophes have already happened, the most devastating being the 2010 ''Deepwater Horizon'' oil spill.
Threats
Pollution
Oil spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into ...
s are one of the greatest threats to the species. Multiple
offshore drilling
Offshore drilling is a mechanical process where a wellbore is drilled below the seabed. It is typically carried out in order to explore for and subsequently extract petroleum that lies in rock formations beneath the seabed. Most commonly, the te ...
operations take place in the Gulf of Mexico, many nearby the Rice's whale core habitat range. Accidents from these operations can release huge quantities of
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
into the ocean, which can inflict a range of harmful to lethal effects to marine life including
respiratory
The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gre ...
,
digestive, and
endocrine
The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the ...
disruption, impaired vision, reproductive failure, increased susceptibility to diseases, and direct poisoning. In Rice's whales, contact with oil can also directly damage their baleen and thereby impair the ability to feed. Large oil spills require tremendous human effort to clean up, and some of the most efficient methods in doing so such as the use of
dispersant
A dispersant or a dispersing agent is a substance, typically a surfactant, that is added to a suspension of solid or liquid particles in a liquid (such as a colloid or emulsion) to improve the separation of the particles and to prevent their set ...
s can themselves be toxic to the whale. In addition, oil residue can persist in the environment and inflict long-term damage. Oil spills in the Gulf of Mexico are frequent; between 2011 and 2013 alone there were 46 oil spills that released the equivalent of nearly one thousand barrels of oil into the Gulf. The 2010 ''Deepwater Horizon'' oil spill, the largest oil spill in world history and the worst environmental disaster in U.S. history, released nearly of oil and took place within close proximity of the Rice's whale habitat.
A 2015 study to assess the damage inflicted to the species' population found that the oil covered 48% of the core habitat range and reduced the population by 22%: 17% of Rice's whales were killed, 22% of females suffered reproductive failure, and 18% of whales suffered adverse health effects.
Plastic ingestion as a product of increased
plastic pollution
Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are cate ...
is another documented source of mortality. The holotype USNM 594665 is currently the only recorded case of death via plastic ingestion. A sharp piece of plastic in size was discovered inside its
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
that
lacerated
A wound is a rapid onset of injury that involves lacerated or punctured skin (an ''open'' wound), or a contusion (a ''closed'' wound) from blunt force trauma or compression. In pathology, a ''wound'' is an acute injury that damages the epider ...
the gastric organ, causing internal bleeding and acute gastric
necrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dig ...
that led to the whale's stranding and death.
However, the NOAA deemed plastic ingestion as a likely low threat to Rice's whales given that such incidents are generally rare in the Gulf of Mexico; less than one percent of stranded marine mammals in the Gulf between 2000 and 2014 showed evidence of ingesting debris. However, it was acknowledged that marine mammal stranding data may not be comprehensive enough.
Vessel collision and entanglement

Collision with ships has been documented in Rice's whales. The lactating female from Tampa Bay (USNM 593536) showed signs of severed vertebrae, lung damage, and internal bruises consistent with a death by a ship strike. In 2019, a live Rice's whale was sighted with a severely deformed spine behind the dorsal fin, damage that is also consistent with vessel collision. The diel vertical diving pattern of the Rice's whale makes it especially susceptible to such collision accidents, given that they may spend the majority of their nighttime hours within of the surface, which is also the range that puts cetaceans at the greatest risk of colliding with ships.
In addition, the whales are known to at times to be curious around ships and periodically approach them to investigate.
Rice's whale's most important habitats in the De Soto Canyon and the adjacent continental slope off western Florida are within zones that saw on average 1-25 ships in vessel traffic between 2009 and 2010, but a few shipping lanes that can see up nearly a hundred ships per year also pass through the habitat zone. Some areas in the Gulf of Mexico's northwestern side that have seen nearby occasional Rice's whales are some of the busiest sectors of the Gulf, with hundreds to up to over a thousand ships transiting the area in one year. The lack of quantity in documented ship strikes in the species does not discount its factor as a major anthropomorphic threat. Vessel collisions with cetaceans are generally underreported, and the rarity of Rice's whales would make this issue even greater.
The Rice's whale's usual habitat also overlaps with deep-water reef fish fisheries, which operate by dropping bottom longline nets at the seafloor between depths of during daytime hours to catch
yellowedge groupers,
tilefish
250px, Blue blanquillo, ''Malacanthus latovittatus''
Tilefishes are mostly small perciform marine fish comprising the family Malacanthidae. They are usually found in sandy areas, especially near coral reefs.
Commercial fisheries exist for t ...
, and sharks. As this is around the time when Rice's whales feed in the same depths, there is a risk of entanglement with the seafloor nets.
One genetically unconfirmed Rice's whale that washed up in 1974 was determined to have been killed by gear entanglement.
Underwater noise
A multitude of anthropogenic noises are produced in great quantities from industrial activities throughout the Gulf of Mexico that can harm baleen whales. The loudest and most frequent are
seismic surveys
Seismology (; from Ancient Greek σεισμός (''seismós'') meaning " earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through o ...
associated with offshore oil and gas activities, which occur on a 24 hours per day and 365 days per year basis. Surveys operate by blasting sound waves into the ocean using airguns at frequencies between 5–300 Hz, intensities as high as 260
dB, and pulse rates of one blast every 10–20 seconds. Cetaceans can obtain permanent hearing loss when exposed to sound intensities of 230 dB or higher. As sound levels diminish rapidly as it travels through the water, this type of damage will only occur to whales that are within to of a 260 dB airgun. As mitigation, seismic surveys are often mandated to be accompanied by protected species observers and to immediately cease operations whenever within of a whale.
Another major source of underwater noise is vessel traffic, which contributes significantly to low-frequency noise pollution in the Gulf of Mexico. Scientists expect that this will increase in the future as the Gulf becomes a more commercially important area thanks to developments such as the expansion of the
Panama Canal
The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a Channel ( ...
. Shipping noise frequencies often overlap with the acoustics of baleen whales. This can cause
auditory masking
In audio signal processing, auditory masking occurs when the perception of one sound is affected by the presence of another sound.Gelfand, S.A. (2004) ''Hearing – An Introduction to Psychological and Physiological Acoustics'' 4th Ed. New York, ...
, which can diminish or block a whale's ability to communicate or detect environmental cues. To work around this problem, the whale may alter its vocalization behavior, but this can further disrupt its communication abilities. In addition, frequent exposure to underwater noise generates a high level of stress for receiving whales, which can alter stress hormone levels, feeding behavior, or cause habitat displacement in avoidance of the noise. Impacts specific to the Rice's whale have yet to be studied, but research on other baleen whales indicates that adverse effects to vessel noise are universal. Studies of Atlantic right whales, whose vocal frequencies are similar to that of Rice's whales and thus may be of similar impact, predicted that vessel noise reduces their communication space by 77%.
See also
*
Environmental impact of the ''Deepwater Horizon'' oil spill
*
List of cetaceans
Cetacea is an infraorder that comprises the 94 species of whales, dolphins, and porpoises. It is divided into toothed whales (Odontoceti) and baleen whales (Mysticeti), which diverged from each other in the Eocene some 50 mya (unit), million years ...
*
Baleen whale
Baleen whales ( systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea ( whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in th ...
Footnotes
References
External links
Gulf of Mexico Bryde's WhaleNOAA Lists Gulf of Mexico Bryde’s Whales as Endangered
{{Taxonbar, from=Q105014096
Baleen whales
Mammals described in 2021
Biota of the Gulf of Mexico
Critically endangered fauna of the United States
ESA endangered species
Taxobox binomials not recognized by IUCN