MINKE WHALES

Minke whale /ˈmɪnki/, or lesser rorqual, is a name given to two species of marine mammal belonging to a clade^[1] within the suborder of baleen whales. The minke whale was given its official designation^[2] by Lacepède in 1804,^[3] who described a juvenile specimen of Balænoptera acuto-rostrata.^[4] The name is a partial translation of Norwegian minkehval, possibly after a Norwegian whaler named Meincke, who mistook a northern minke whale for a blue whale.^[5]

Taxonomy

Most modern classifications split the minke whale into two species;

• Common minke whale or northern minke whale (Balaenoptera acutorostrata), and
• Antarctic minke whale or southern minke whale (Balaenoptera bonaerensis).^[6]

 

Taxonomists further categorize the common minke whale into two or three subspecies; the North Atlantic minke whale, the North Pacific minke whale and dwarf minke whale. All minke whales are part of the rorquals, a family that includes the humpback whale, the fin whale, the Bryde's whale, the sei whale and the blue whale.
The junior synonyms for B. acutorostrata are B. davidsoni (Cope 1872), B. minimia (Rapp, 1837) and B. rostrata (Fabricius, 1780). There is one synonym for B. bonaerensis - B. huttoni (Gray 1874).
Writing in his 1998 classification, Rice recognized two of the subspecies of the common minke whale - B. a. scammoni (Scammon's minke whale) and a further (taxonomically) unnamed subspecies found in the Southern Hemisphere, the dwarf minke whale (first described by Best, 1985).^[7]
On at least one occasion, an Antarctic minke whale has been confirmed migrating to the Arctic.^[8][9] In addition, at least two wild hybrids between a common minke whale and an Antarctic minke whale have been confirmed.^[8][9][10]

 

Description

The minke whales are the second smallest baleen whale; only the pygmy right whale is smaller. Upon reaching sexual maturity (6–8 years of age), males measure an average of 6.9 m (23 ft) and females 7.4 m (24 ft) in length, respectively. Reported maximum lengths vary from 9.1 to 10.7 m (30 to 35 ft) for females and 8.8 to 9.8 m (29 to 32 ft) for males. Both sexes typically weigh 4–5 t (3.9–4.9 long tons; 4.4–5.5 short tons) at sexual maturity, and the maximum weight may be as much as 10 t (9.8 long tons; 11 short tons).
The minke whale is a black/gray/purple color. Common minke whales (Northern Hemisphere variety) are distinguished from other whales by a white band on each flipper. The body is usually black or dark-gray above and white underneath. Minke whales have between 240 and 360 baleen plates on each side of their mouths. Most of the length of the back, including dorsal fin and blowholes, appears at once when the whale surfaces to breathe.
Minke whales typically live for 30–50 years; in some cases they may live for up to 60 years.
The brains of minke whales have around 12.8 billion neocortical neurons and 98.2 billion neocortical glia.^[11]

Behavior

Multimedia relating to the minke whale Note that whale calls have been sped up to 10x their original speed.

An Atlantic minke whale Menu 0:00 Problems playing this file? See media help.

 

 

The whale breathes three to five times at short intervals before 'deep-diving' for two to 20 minutes. Deep dives are preceded by a pronounced arching of the back. The maximum swimming speed of minkes has been estimated at 38 km/h (24 mph).

Reproduction

See also: Whale reproduction

The gestation period for minke whales is 10 months, and calves measure 2.4 to 2.8 m (7.9 to 9.2 ft) at birth. The newborns nurse for five to 10 months. Breeding peaks during the summer months. Calving is thought to occur every two years.^[12]

Population and conservation status

The IUCN Red List labels the common minke whale as Least Concern.^[13] The Antarctic minke whale is listed as Data Deficient.^[14]
COSEWIC puts both species in the Not At Risk category [1]. NatureServe lists them as G5 which means the species is secure on global range [2].
In 2012, the Scientific Committee of the International Whaling Commission agreed upon a population estimate of 515,000 for the Antarctic minke stock.^[15] The Scientific Committee acknowledged that this estimate is subject to a negative bias because some minke whales would have been outside the surveyable ice edge boundaries.

Whaling

Main article: Whaling

Norwegian minke whale quotas (blue line, 1994-2006) and catches (red line, 1946-2005) in numbers (From Norwegian official statistics)

Whaling was mentioned in Norwegian written sources as early as the year 800, and hunting minke whales with harpoons was common in the 11th century^{[citation needed]}. In the 19th century, they were considered too small to chase, and received their name from a young Norwegian whale-spotter in the crew of Svend Foyn, who harpooned one, mistaking it for a blue whale and was derided for it.^[16]
By the end of the 1930s, they were the target of coastal whaling by Brazil, Canada, China, Greenland, Japan, Korea, Norway, and South Africa. Minke whales were not then regularly hunted by the large-scale whaling operations in the Southern Ocean because of their relatively small size. However, by the early 1970s, following the overhunting of larger whales such as the sei, fin, and blue whales, minkes became a more attractive target of whalers. By 1979, the minke was the only whale caught by Southern Ocean fleets. Hunting continued apace until the general moratorium on whaling began in 1986.
Following the moratorium, most hunting of minke whales ceased. Japan continued catching whales under the special research permit clause in the IWC convention, though in significantly smaller numbers. The stated purpose of the research is to establish data to support a case for the resumption of sustainable commercial whaling. Environmental organizations and several governments contend that research whaling is simply a cover for commercial whaling. The 2006 catch by Japanese whalers included 505 Antarctic minke whales.
Although Norway initially followed the moratorium, they had placed an objection to it with the IWC and resumed a commercial hunt of the Common minke whale in 1993. The quota for 2006 was set at 1,052 animals, but only 546 were taken.^[17] The quota for 2011 is set at 1286.^[18] In August 2003, Iceland announced it would start research catches to estimate whether the stocks around the island could sustain hunting. Three years later, in 2006, Iceland resumed commercial whaling.
A 2007 analysis of DNA fingerprinting of whale meat estimated South Korean fishermen caught 827 minke between 1999 and 2003,^[19] approximately twice the officially reported number. This raised concerns that some whales were being caught deliberately.

Whale watching

Play media

Common minke whale breaching in the St. Lawrence River near Tadoussac, Quebec

Minke whale in the Ross Sea

Due to their relative abundance, minke whales are often the focus of whale-watching cruises setting sail from, for instance, the Isle of Mull in Scotland, County Cork in Ireland and Húsavík in Iceland, and tours taken on the east coast of Canada. They are also one of the most commonly sighted whales seen on whale-watches from New England and eastern Canada. In contrast to humpback whales, minkes do not raise their flukes out of the water when diving and are less likely to breach (jump clear of the sea surface). This, combined with the fact that minkes can stay submerged for as long as 20 minutes, has led some whale-watchers to label them 'stinky minkes'.^[20]
In the northern Great Barrier Reef (Australia), a swim-with-whales tourism industry has developed based on the June/July migration of dwarf minke whales. A limited number of reef tourism operators (based in Port Douglas and Cairns) have been granted permits by the Great Barrier Reef Marine Park Authority to conduct these swims, given strict adherence to a code of practice, and that operators report details of all sightings as part of a monitoring program. Scientists from James Cook University and the Museum of Tropical Queensland have worked closely with participating operators and the Authority, researching tourism impacts and implementing management protocols to ensure these interactions are ecologically sustainable.
Minke whales are also occasionally sighted in Pacific waters, in and around the San Juan Islands of Washington State.

AMMAZON RIVER DOLPHINS

Inia geoffrensis, commonly known as the Amazon river dolphin, or Pink River Dolphin is a freshwater river dolphin endemic to the Orinoco, Amazon and Araguaia/Tocantins River systems of Brazil, Peru, Bolivia, Ecuador, Colombia and Venezuela. It was previously listed as a vulnerable species by the IUCN due to pollution, overfishing, excessive boat traffic and habitat loss but in 2011 it was changed to data deficient due to a lack of current information about threats, ecology, and population numbers and trends.^[1]
Other common names of the species include boto, boto cor-de-rosa, boto vermelho, bouto, bufeo, tonina and pink dolphin.^[1]

Description

The Amazon river dolphin is one of the river dolphins formerly included in the superfamily Platanistoidea, making it paraphyletic; it has since been moved to Inioidea. Although not a large cetacean in general terms, this dolphin is the largest freshwater cetacean; it can grow larger than a human. Body length can range from 1.53 to 2.4 m (5.0 to 7.9 ft), depending on subspecies. Females are typically larger than males.^{[citation needed]} The largest female Amazon river dolphins can range up to 2.5 m (8.2 ft) in length and weigh 98.5 kg (217 lb). The largest male dolphins can range up to 2.0 m (6.6 ft) in length and weigh 94 kg (207 lb).^[2][3]
They have unfused neck vertebrae, enabling them to turn their heads 90 degrees. Their flexibility is important in navigating through the flooded forests. Also, they possess long beaks which contain 24 to 34 conical and molar-type teeth on each side of the jaws.^[4]
In colour, these dolphins can be either light gray or carnation pink.

Taxonomy

The species was described by Henri Marie Ducrotay de Blainville in 1817. Rice's 1998 classification^[5] lists a single species, Inia geoffrensis in the genus Inia, with three recognised subspecies. Some older classifications, as well as some recent publications,^[6] listed the boliviensis population as a separate species. In 2012 the Society for Marine Mammalogy^[7] began considering the Bolivian (Inia geoffrensis boliviensis) and Amazonian (Inia geoffrensis geoffrensis) subspecies as full species Inia boliviensis and Inia geoffrensis, respectively; however, much of the scientific community consider the boliviensis population to be a subspecies of Inia geoffrensis. The genus Inia separated from its sister taxon during the Miocene epoch.^[8]
The two currently recognized species are:

• I. g. geoffrensis — distributed in the Amazon and Araguaia/Tocantins basins (excluding the Madeira River drainage, upstream of the Teotonio Rapids in Rondônia)
• I. g. humboldtiana — distributed in the Orinoco basin
• I. boliviensis — distributed in the Bolivian sub-basin of the Amazon basin upstream of the Teotonio Rapids in Rondônia

The Amazon river dolphin is closely related to the newly identified Araguaian river dolphin which is believed to have become physically separated and diverged into two separate species. Araguaian Boto have fewer rows of teeth than their closely related Amazon Boto.^[9]

Ecology

The Amazon river dolphin is found throughout the Amazon and Orinoco. It is particularly abundant in lowland rivers with extensive floodplains. During the annual rainy season, these rivers flood large areas of forests and marshes along their banks. The Amazon river dolphin specialises in hunting in these habitats, using its unusually flexible neck and spinal cord to maneuver among the underwater tree trunks, and using its long snout to extract prey fish from hiding places in hollow logs and thickets of submerged vegetation.
When the water levels drop, the dolphins move either into the main river channels or into large lakes in the forest, and take advantage of the concentrated prey in these reduced water bodies. They feed on crustaceans, crabs, small turtles, catfish, piranha, shrimp, and other fish.^[4]

Behavior

Adult males have been observed carrying objects in their mouths, objects such as branches or other floating vegetation, balls of hardened clay. The males appear to carry these objects as a socio-sexual display which is part of their mating system. The behaviour is "triggered by an unusually large number of adult males and/or adult females in a group, or perhaps it attracts such into the group. A plausible explanation of the results is that object carrying is aimed at females and is stimulated by the number of females in the group, while aggression is aimed at other adult males and is stimulated by object carrying in the group."^[10]
The male reaches sexual maturity at about 2 metres (6.6 ft) and the female at about 1.7 metres (5.6 ft). Most calves are born between July and September after a gestation period of 9 to 12 months; they are about 0.81 metres (2.7 ft) long at birth and weigh about 6.8 kilograms (15 lb).^[4] The young follow their parents closely for a few months, and often two adults are seen swimming with two or more small juveniles.

Human interaction

A trained Amazon river dolphin at the Acuario de Valencia

The Amazon river dolphin is listed on appendix II^[11] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II as it has an unfavourable conservation status or would benefit significantly from international co-operation organized by tailored agreements. In September 2012, Bolivian President Evo Morales enacted a law to protect the dolphin and declared it a national treasure.^[12]
 The region of the Amazon in Brazil has an extension of 5 million km² containing diverse fundamental ecosystems.^[13][14] One of these ecosystems is a floodplain, or a várzea forest, and is home to a large number of fish species which are an essential resource for human consumption.^[15] The várzea is also a major source of income through excessive local commercialized fishing.^[13][16][17] Várzea consist of muddy river waters containing a vast number and diversity of nutrient rich species.^[10] The abundance of distinct fish species is what lures in the Amazon River dolphin into the várzea areas of high water occurrences during the seasonal flooding.^[18]
In addition to attracting predators such as the Amazon River dolphin, these high water occurrences are an ideal location to draw in the local fisheries. Human fishing activities directly compete with the Amazon River dolphins for the same fish species, the tambaqui (Colossoma macropomum) and the Pirapatinga (Piaractus brachypomus), resulting in deliberate or unintentional catches of the Amazon River dolphin.^{[19][20][21][13][22][23][24][25]} The local fishermen overfish and when the Amazon River dolphins remove the commercialized fish from the nets and lines, it causes damages to the equipment and the capture, as well as a negative reaction from the local fishermen.^{[21] [23][24]} The negative reactions of the local fishermen is also attributed to the Brazilian Institute of Environment and Renewable Natural Resources prohibiting from killing the Amazon River dolphin, yet not compensating the fishermen for the damage done to their equipment and capture.^[25]
During the process of catching the commercialized fish, the Amazon River dolphins will get caught in the nets and exhaust themselves until they die, or the local fishermen will deliberately kill the Amazon River dolphins that become entangled in their nets.^[15] The carcasses of the Amazon River dolphins are disposed of, consumed, or used as bait to attract a scavenger catfish, the piracatinga (Calophysus macropterus).^[15][26] The usage of the Amazon River dolphin carcass as bait for the piracatinga dates back from 2000.^[26] The increasing consumption demand by the local inhabitants and Colombia for the piracatinga, has created a market for distribution of the Amazon River dolphin carcasses to be used as bait throughout these regions.^[25]
Of the 15 Amazon River dolphins that were found in the Japurá River, 73% of the carcasses were killed for bait, disposed of, or abandoned in entangled gillnets.^[15] It is important to note that the data does not fully represent the actual overall number of deaths of the Amazon River dolphins, whether accidental or intentional, because a variety of factors make it extremely complicated to record and medically examine all the carcasses.^[15][20][23] Scavenger species feed upon the carcasses and the complexity of the river currents make it nearly impossible to locate all the carcasses.^[15] More importantly, the local fishermen do not report these deaths out of fear that a legal course of action will be taken against them,^[15] as the Amazon River dolphin and other cetaceans are protected under the Brazilian Federal Law prohibiting any takes, harassments, and kills of the species.^[27]

In popular culture

 
 In traditional Amazon River folklore, at night, an Amazon river dolphin becomes a handsome young man who seduces girls, impregnates them, and then returns to the river in the morning to become a dolphin again. This dolphin shapeshifter is called an encantado. It has been suggested that the myth arose partly because dolphin genitalia bear a resemblance to those of humans. Others believe the myth served (and still serves) as a way of hiding the incestuous relations which are quite common in some small, isolated communities along the river.^[28] In the area, there are tales that it is bad luck to kill a dolphin. Legend also states that if a person makes eye contact with an Amazon river dolphin, he or she will have lifelong nightmares. Local legends also state that the dolphin is the guardian of the Amazonian manatee, and that, should one wish to find a manatee, one must first make peace with the dolphin.
Associated with these legends is the use of various fetishes, such as dried eyeballs and genitalia.^[28] These may or may not be accompanied by the intervention of a shaman. A recent study has shown, despite the claim of the seller and the belief of the buyers, none of these fetishes are derived from the boto. They are derived from Sotalia guianensis, are most likely harvested along the coast and the Amazon River delta, and then are traded up the Amazon River. In inland cities far from the coast, many, if not most, of the fetishes are derived from domestic animals such as sheep and pigs.^[29]

THE COMMON DOLPHINS

The common dolphin is the name given to two species (and possibly a third) of dolphin making up the genus Delphinus.
Prior to the mid-1990s, most taxonomists only recognised one species in this genus, the common dolphin Delphinus delphis. Modern cetologists usually recognise two species — the short-beaked common dolphin, which retains the systematic name Delphinus delphis, and the long-beaked common dolphin Delphinus capensis.
The common dolphin is not the dolphin of popular imagination despite its name; that distinction belongs to the bottlenose dolphin due to its widespread use in marine parks and its appearance in the television series Flipper.^[1] However, this dolphin was the most frequently represented in the art and literature of ancient Greece and Rome.^[2]

 

Physical characteristics

Both common dolphin species are medium-sized; adults range between 1.9 and 2.5 m (6.2 and 8.2 ft) long, and can weigh between 80 and 235 kg (176 and 518 lb), although the range between 80 and 150 kg (180 and 330 lb) is more common.^[3] Males are generally longer and heavier.^[3] The color pattern on the body is unusual. The back is dark and the belly is white, while on each side is an hourglass pattern colored light grey, yellow, or gold in front and dirty grey in back.^[4] They have long, thin rostra with up to 50–60 small, sharp, interlocking teeth on each side of each jaw.^[5]

Differentiating species

Common dolphin, Ireland

Despite the historic practice of lumping the entire Delphinus genus into a single species, these widely distributed dolphins exhibit a wide variety of sizes, shapes and colors. Indeed, over the past few decades, over 20 distinct species in the genus have been proposed. Scientists in California in the 1960s concluded there were two species — the long-beaked and short-beaked. This analysis was essentially confirmed by a more in-depth genetic study in the 1990s. This study also suggested a third species (D. tropicalis, common name usually Arabian common dolphin), characterized by an extremely long and thin beak and found in the Red Sea and Indian Ocean, might be distinguished from the long-beaked species. The current standard taxonomic works recognize this as just a regional variety. D. tropicalis is a subspecies of D. capensis.

Natural history

Common dolphin, Ireland

Common dolphins live in both warm-temperate and tropical waters ranging from 40–60°N to 50°S. Long-beaked common dolphins mostly inhabit shallow, warm costal water.^[6] Short-beaked common dolphins are common "along shelf edges and in areas with sharp bottom relief such as seamounts and escarpments".^[4] Common dolphin have a varied diet consisting of many species of fish and squid. This includes both mesopelagic species and epipelagic schooling species. They have been recorded to make dives up to 200 metres (660 ft) deep.
Common dolphins can live in aggregations of hundreds or even thousands of dolphins.^[6] They sometimes associate with other dolphin species, such as pilot whales.^[6] They have also been observed bow riding on baleen whales, and they also bow ride on boats.^[6] They are fast swimmers (up to 60 km/h), and breaching behavior and aerial acrobatics are common with this species.^[3] They are also known to display altruistic behaviors to support injured members.^[7][8]
The short-beaked common dolphin has a gestation period of 10 to 11 months.^[6] The newborn calf has a length of 70 to 100 centimetres (2.3 to 3.3 ft) and weighs about 10 kilograms (22 lb).^[3] For the Black Sea population, weaning occurs at between five and six months, but occurs later (up to about 19 months) in other areas.^[3][6] Typical interbirth interval ranges from one year for the Black Sea population to three years for eastern Pacific Ocean populations.^[6] Age of sexual maturity also varies by location, but can range between two and seven years for females and three and 12 years for males.^[3][6] No evidence exists of any major reproductive differences between the two species.^[4] In captivity, the long-beaked common dolphin has hybridized with the common bottlenose dolphin (Tursiops truncatus).^[6] One of the hybrids has been bred back to a bottlenose dolphin, demonstrating such hybrids are fertile.^[9]

 

Human interactions

Conservation

A Common Dolphin jumping off Morro Bay Nature Reserve

Common dolphins face a mixture of threats due to human influence. Moderate levels of metal pollutants, which are thought to negatively impact dolphin health,^[10] have been measured in some populations.^[11] Populations have been hunted off the coast of Peru for use as food and shark bait. In most other areas, the dolphins have not been hunted directly. Several thousand individuals have been caught in industrial trawler nets throughout their range. Common dolphins were abundant in the western Mediterranean Sea until the 1960s but occurrences there have tailed off rapidly. The reasons are not well understood, but are believed to be due to extensive human activity in the area. In the US, they are a protected species and sometimes are caught by accident in some trawler nets as bycatch, though despite this they are still quite common throughout their range. Despite these potential threats, the short-beaked common dolphin is considered to be Least Concern by the IUCN Red List, and the long-beaked common dolphin is listed as Data Deficient.^[12]
The short-beaked common dolphin Delphinus delphis is listed globally on Appendix II^[13] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).^[14] As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009 of the Convention on the Conservation of Migratory Species of Wild Animals (CMS) as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements. The Mediterranean population of the short-beaked common dolphin is also listed on Appendix I,^[13] as this population has been categorized as being in danger of extinction throughout all or a significant proportion of their range and CMS Parties strive towards strictly protecting these animals, conserving or restoring the places where they live, mitigating obstacles to migration and controlling other factors that might endanger them. In addition, the species is also covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS)^[15] and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS).^[16]

Captivity

Common dolphins are not common in captivity. But on at least three occasions, a beached common dolphin in California was nursed back to health at SeaWorld San Diego, but deemed unfit to release back to the ocean. These common dolphins remained at SeaWorld with the bottlenose dolphin exhibit. On one occasion, a male common dolphin managed to impregnate one of the female bottlenose dolphins in the exhibit, leading to four hybrid births.^[9] One of the resulting common dolphin/bottlenose dolphin hybrids remained at SeaWorld, San Diego (alternately under the name Cindy or Bullet) while the other was kept at Discovery Cove. They also participate in shows with bottlenose dolphin and pilot whale at Sea World.
Other than at SeaWorld, at least 90 common dolphins are known to have been captured from the wild and kept in captivity. Captured common dolphins are said to be difficult to keep in captivity.^[5]

COMMERSON'S DOLPHINS

Commerson's dolphin (Cephalorhynchus commersonii) is one of four dolphins in the genus Cephalorhynchus. The species has also the common names skunk dolphin, piebald dolphin and panda dolphin. The dolphin is named for Philibert Commerson, who first described them in 1767 after he sighted them in the Strait of Magellan.^[3]

Physical description

A Commerson's dolphin in the Strait of Magellan

Commerson's dolphin has a very distinctive patterning. It has a black head, dorsal fin, and fluke, with a white throat and body. The demarcation between the two colours is very clear-cut. This stocky creature is one of the smallest of all cetaceans growing to around 1.5 m (5 ft). A mature female caught off of south Patagonia, at 23 kg (51 lb) and 1.36 m (4.5 ft), may be the smallest adult cetacean on record.^[4] Its appearance resembles that of a porpoise, but its conspicuous behaviour is typical of a dolphin. The dorsal fin has a long, straight leading edge which ends in a curved tip. The trailing is typically concave but not falcate. The fluke has a notch in the middle. This dolphin has no rostrum. It is not known why their distribution is limited to the southern coast of South America and the Kerguelen Islands.
Sexes are easily distinguished by the different shape of the black blotch on the belly — it is shaped like a teardrop in males but is more rounded in females. Females reach breeding age at six to 9 years. Males reach sexual maturity at about the same age. Mating occurs in the spring and summer and calving occurs after a gestation period of 11 months. The oldest known Commerson's dolphin died at age 18.

 

 

 

Population and distribution

 
 The species is distributed in two locations. The larger population is found inshore in various inlets in Argentina, in the Strait of Magellan and near the Falkland Islands. The second population (discovered in the 1950s) resides near the Kerguelen Islands, 8,000 km (5,000 mi) to the east of the main population. They prefer shallow waters. Global populations are unknown, but the species is accepted to be locally common. A survey in 1984 estimated there to be 3,400 individuals in the Strait of Magellan.
The dolphin is found in two geographically disparate areas:

• the southern coast of South America around Puerto Deseado, Tierra del Fuego and the Falkland Islands, and
• waters near the Kerguelen Islands in the southern part of the Indian Ocean.

Behavior

Commerson's dolphin is very active. It is often seen swimming rapidly on the surface and leaping from the water. It also spins and twists as it swims and may surf on breaking waves when very close to the shore. It will bow-ride and swim behind fast-moving boats. It is also known to swim upside-down, which is thought to improve the visibility of its prey.
This dolphin feeds on a mix of coastal and pelagic fish and squid. Those in the South American subpopulation supplement their diets with crustaceans.

Conservation

The IUCN lists Commerson's dolphin as Data Deficient in its Red List of Threatened Species. The proximity of the dolphin to the shore makes accidental killing in gillnets a common occurrence. The dolphin was killed for use as crab bait by some Argentinian and Chilean fishermen in the 1970s and 1980s, but this practice has since been curtailed.^[2]
The Commerson's dolphin population of South America is listed on Appendix II^[5] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II^[5] as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.^[6]

Captivity

About two dozen Commerson's dolphins live in aquariums in the world, including SeaWorld San Diego, Aquatica in Florida, Duisburg Zoo in Germany (until 2004), and several aquariums in Japan.

THE ATLANTICA SPOTTED DOLPHINS

The Atlantic spotted dolphin (Stenella frontalis) is a dolphin found in the Gulf Stream of the North Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their bodies.

 

 

 Taxonomy

The Atlantic spotted dolphin was first described by Cuvier in 1828. Considerable variation in the physical form of individuals occurs in the species, and specialists have long been uncertain as to the correct taxonomic classification. Currently, just one species is recognised, but a large, particularly spotty variant commonly found near Florida quite possibly may be classified as a formal subspecies or indeed a species in its own right.
Atlantic spotted dolphins in the Bahamas have been observed mating with bottlenose dolphins.^[3] Rich LeDuc has published data that suggest the Atlantic spotted dolphin may be more closely related to bottlenose dolphin (genus Tursiops) than to other members of the genus Stenella.^[3]

Description

Stenella frontalis, La Gomera

Near South Caicos, Turks and Caicos Islands

A juvenile swimming in the blue water

The coloring of the Atlantic spotted dolphin varies enormously as they grow. Calves are a fairly uniform grey colour. When the calves are weaned, they then begin to get their spots. Juveniles have some dark spots on their bellies, and white spots on their flanks. Their back and dorsal fins are a darker grey than the rest of the body. As the animal matures, the spots become denser and spread until the body appears black with white spots at full maturation.
The Atlantic spotted dolphin has a three-part coloration: dark gray back, lighter sides, and a white belly.
Measurements at birth:

Length: about 35–43 in (89–109 cm)

Weight:

Maximum measurements:

Length:

Male 2.26 m (7 ft 5 in)

Female 2.29 m (7 ft 6 in)

Weight: 310

Male 140 kg (310 lb)

Female 130 kg (290 lb)

This is a medium-sized dolphin in both length and weight. At full size, South American spotted dolphins are about 2.2-2.5 m in length. Compared to the much smaller pantropical spotted dolphin, the Atlantic spotted dolphin is more robust. It lives in common waters with the pantropical spotted dolphin and the bottlenose dolphin.
In common with other species in its genus, the Atlantic spotted dolphin is a gregarious creature. It is a fast swimmer and keen bow-rider, and prone to acrobatic aerial displays.

Population and distribution

 

The species is endemic to the temperate and tropical areas of the Atlantic Ocean. It has been widely observed in the western end of the Gulf Stream, between Florida and Bermuda. Off the Bahamas, tourism industries to swim with dolphins are available.^[4] It is also present in the Gulf of Mexico. More infrequent sightings have been made further east, off the Azores and Canary Islands. Northerly sightings have been made as far north as Cape Cod across to the southwestern tip of Spain. They are certainly present further south, too, as far as Rio Grande do Sul in Brazil and across to west Africa, but their distribution is poorly understood in these areas.
About 20 years ago, only about 80 dolphins were in the Bahamas. Now, almost 200 dolphins are found there. On account of their similar appearance to other dolphins in their range, it is difficult to be sure of the Atlantic spotted dolphin's population. A conservative estimate is around 100,000 individuals.

Human interaction

Some Atlantic spotted dolphins, particularly some of those are around the Bahamas, have become habituated to human contact. In these areas, cruises to watch and even swim with the dolphins are common.
Atlantic spotted dolphins are an occasional target of harpoon fishermen, and every year some creatures are trapped and killed in gill nets, but these activities are not currently believed to be threatening the survival of the species. This species lives in the mesopelagic layer of the ocean. These dolphins are not threatened by extinction, however, commercial trade may affect their evolution and sustainability. Sometimes they are killed by harpoons off St. Vincent.

Conservation

The Atlantic spotted dolphin is included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia^[5]

THE PANTROPICAL SPOTTED DOLPHINS

The pantropical spotted dolphin (Stenella attenuata) is a species of dolphin found in all the world's temperate and tropical oceans. The species was beginning to come under threat due to the killing of millions of individuals in tuna purse seines. In the 1980s, the rise of "dolphin-friendly" tuna capture methods saved millions of the species in the eastern Pacific Ocean and it is now one of the most abundant dolphin species in the world.

Taxonomy

The species was first described by John Gray in 1846. Gray's initial analysis included the Atlantic spotted dolphin in this species. They are now regarded as separate. Both the genus and specific names come from Latin words meaning thin or thinning.
Three subspecies are recognised in Rice's 1998 survey of cetacean taxonomy. Two of these have not been formally named.

S. a. subspecies A, the off-shore form found in the eastern Pacific

S. a. subspecies B, a form found around the Hawaiian Islands

S. a. graffmani, a coastal form found from Mexico to Peru

S. a. attenuata.

Physical description

Pantropical spotted dolphins porpoising

The pantropical spotted dolphin varies significantly in size and colouration throughout its range. The most significant division is between coastal and pelagic varieties. The coastal form is larger and more spotted. (These two forms have been divided into subspecies only in eastern Pacific populations).
Spots are key defining characteristics in adults, though immature individuals are generally uniformly coloured and susceptible to confusion with the bottlenose dolphin. Populations around the Gulf of Mexico may be relatively spot-free even in adulthood. In the Atlantic, confusion is possible with the Atlantic spotted dolphin.
Broadly speaking, the dolphin has a long, thin beak. The upper and lower jaws are darkly coloured, but are separated by thin, white "lips". The chin, throat, and belly are white to pale grey with a limited number of spots. The flanks are separated into three distinct bands of colour — the lightest at the bottom, followed by a thin, grey strip in the middle of the flank, and a dark-grey back. The tall concave dorsal fin is similarly coloured. The thick tail stock matches the colour of the middle band.
The pantropical spotted dolphin is very active and is prone to making large, splashy leaps from the sea. It is a common breacher and will often clear the water for a second or more. Bow-riding and other play with boats is common.
In the eastern Pacific, the dolphin is often found swimming with yellowfin tuna (hence the problem with dolphin deaths caused by tuna fishing). However, they do not feed on that fish. In fact, the two species have similar diets of small epipelagic fish. In other areas, the species may also feed on squid and crustaceans.
Birth length is 80-90 cm. Adults are about 2.5 m long and weigh 120 kg. Sexual maturity is reached at 10 years in females and 12 years in males. The average lifespan is around 40 years.

Population and distribution

 
The pantropical spotted dolphin, as its name implies, is found across all tropical and subtropical waters around the world — roughly speaking all oceans and seas between 40°N and 40°S. The total world population is in excess of three million — the second-most abundant cetacean after the bottlenose dolphin — of which two million are found in the eastern Pacific. However, this represents a decrease from at least 7 million since the 1950s.
Centres of highest population density are the shallow warmest waters (water temperature in excess of 25°C). They also tend to concentrate where a high temperature gradient is found.

Human interaction

Dolphin swimming ahead of the NOAA Ship Rude

The pantropical spotted dolphin's propensity for associating with tuna, particularly in the eastern Pacific, has in recent history been a very real danger. In the 1960s and 1970s, fishermen would capture thousands of dolphin and tuna at once using purse seine nets. The dolphins all died. Over a period of about 25 years, 75% of this region's population, and over half the world's total were wiped out. The issue has received wide public attention. Many major supermarkets have found it economically expedient to use tuna suppliers whose fisherman catch tuna by more discriminatory means, and thus advertise their tuna product as dolphin-friendly. Some such products are approved by the Whale and Dolphin Conservation Trust.^[3]
Negative impacts from fishing activities remain, despite broad “dolphin safe” practices. Instead of reducing numbers through direct mortalities, fishing activities have disrupted the reproductive output of the northeastern pantropical spotted dolphin. The fishing had a negative impact on calf survival rates and/or birth rates. This could be caused when fishing operations separate mothers from their suckling calves, interfere with the conception or gestation of calves, or a combination of the two.^[4]

Conservation

 

The eastern tropical Pacific and Southeast Asian populations of the pantropical spotted dolphin are listed in Appendix II^[5] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As the pantropical spotted dolphin can be divided into three subspecies, studies of these distinct populations would be needed to assess conservation efforts.^[6]
In addition, the pantropical spotted dolphin is covered by the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU) and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).^[7]