Delphinidae

Diversity

The family Delphinidae , collectively called oceanic dolphins or delphinids, contains 37 different species in 17 genera. Oceanic dolphins have vary in morphology, but generally have streamlined bodies with prominent dorsal fins and beaks with conical teeth. They also have fatty deposits in their foreheads, called melons, which aid in communication and echolocation. In some oceanic dolphin species, the melon protrudes roughly the same length as the snout, but most species have prominent snouts that extend beyond their melons. Species in the family Delphinidae range in size, with orcas ( Orcinus orca ) being the largest (almost 10 m long) and Hector's Dolphins ( Cephalorhynchus hectori ) being the shortest (up to 1.2 m long). Delphinids also vary in coloration, though they generally have patterns white, black, and grey.

Oceanic dolphin species live in oceans, seas, estuaries, and some rivers. They are fast and agile swimmers, using echolocation and often social coordination to hunt their prey. Many oceanic dolphins are social, living in groups called pods that range in size, depending on the species. Social delphinids exhibit complex social behaviors related to hunting, breeding, and raising young. They are considered to be highly intelligent, but are relatively poorly studied.

Geographic Range

There are species in the family Delphinidae that live in oceans and seas around the world, as well as a few species that live in estuaries or large rivers. Some oceanic dolphins live primarily in coastal waters while others live primarily in the open ocean. Oceanic dolphins are highly social, typically living in groups that range in size from small family groups to many thousands of individuals.

• Biogeographic Regions
• arctic ocean arctic ocean
  • native native
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

Habitat

Oceanic dolphins inhabit a variety of marine and freshwater environments. Some species live in coastal waters, estuaries, or rivers, while others spend much of their time in the open ocean. Some species live entirely in river systems while others live in coastal marine areas and travel up rivers to find prey. Most delphinids are smaller than members of other whale families, and do not exhibit the same deep diving behaviors or migratory behaviors that other whale groups do. They are capable of moving long distances, but typically only do so to find food or conduct reproductive activities, such as breeding and rearing young. Most oceanic dolphin species rest in calm waters with only half their brain active for around 8 hours a day. When fully awake, they hunt or socialize in shallow waters or in the open ocean close to the surface. Delphinids exhibit playful social behaviors such as riding waves, leaping out of water, and interacting with conspecifics near the surface.

• Habitat Regions
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• pelagic pelagic
• reef reef
• rivers and streams
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Systematic and Taxonomic History

Oceanic dolphins share a common ancestor with porpoises (family Phocoenidae ), but the two groups diverged at some point during the Miocene epoch, between 5.3 and 23 million years ago. Species in the family Delphinidae vary widely in morphology. Many taxonomic relationships within the family are still in question and are being updated as more genetic research is conducted. When the family Delphinidae was first established, there were around 32 recognized species; there are currently 37 species and 19 genera recognized as delphinids.

Physical Description

Oceanic dolphins have diverse morphologies have a wide range of possibilities within the family. In general, members have streamlined, torpedo-shaped bodies with notched tails and a fatty organ in their foreheads called a melon. The melon functions as a lens to focus sound, which aids in communication and echolocation. Most delphinids have long beaks that protrude beyond their melons, but some species, such as orcas ( Orcinus orca ) or Irrawaddy dolphins ( Orcaelle brevirostris ) have shorter beaks that end just below their melons. Oceanic dolphins all have blowholes immediately posterior to their melons and a dorsal fin between their blowholes and their tails. All oceanic dolphins also have two pectoral flippers. There is no consistent sexual dimorphism, although males are larger than females in some species. Delphinids vary in coloration and patterning, but are mostly grey, white, black, or sometimes pink in color. Countershading is common among members of the family Delphinidae . Unlike other groups of whales, which often have barnacles growing on their skin, oceanic dolphins regularly shed their skin to remove parasites.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• male larger

Reproduction

Oceanic dolphins are iteroparous and polygynandrous. When male delphinids reach sexual maturity, they leaving the maternity pods where they were raised and form pods with other reproductive males. Most delphinids reproduce throughout the year, with males performing courtship behaviors to attract mates. Courtship displays vary between species, but include behaviors such as physical rubbing, gift giving, acrobatic displays, harassment of females, or competition with other males.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Male delphinids typically reach sexual maturity after 8 to 14 years, whereas females reach sexual maturity after 5 to 10 years. Once males reach sexual maturity, they leave the pods in which they were raised and join pods of other reproductive males. Females gestate their young for 10 to 15 months before giving birth. Females that are pregnant or actively raising young form maternity pods and help each other during the birthing process. Calves are weaned by 18 months at the latest, but they stay in the same pod as their mothers for up to 6 years.

Even before they reach sexual maturity, delphinids within the same pod display social behaviors similar to those involved in courtship, such as physical rubbing or playing, although they perform these behaviors with group members regardless of their sex. Rubbing is an important precopulatory behavior, because delphinids maintain belly-to-belly physical contact while mating.

• Key Reproductive Features
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Female delphinids exhibit extended parental care, whereas males exhibit no parental investment beyond the act of mating. Females that are pregnant or raising calves form groups called maternity pods. Depending on the species, calves may not be fully weaned until they are as much as 18 months old. Some delphinids continue to nurse even after they begin to eat solid food. Newborn and juvenile delphinids spend much of their time immediately beside their mothers, where they are protected. Juveniles also exert less energy when swimming by taking advantage of the slipstream created by their mothers. Oceanic dolphins exhibit an extended period of association with their mothers, spending as much as 6 years in the same pod before becoming independent. During this time, juvenile delphinids learn to forage and avoid predation effectively.

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• post-independence association with parents
• extended period of juvenile learning

Lifespan/Longevity

The lifespans of delphinids vary greatly depending on the species. Most species live at least 10 to 20 years in the wild, unless they are killed by predators or poachers. Some species, such as bottlenose dolphins (genus Tursiops ), live up to 60 years. Most oceanic dolphins have shorter lifespans when kept in captivity, especially when they are isolated from conspecifics.

Behavior

Members of the family Delphinidae are highly social. They travel and forage in groups, called pods, and take turns with other pod members when resting. Females and their offspring form groups called maternity pods, while reproductive males often form bachelor pods. Juveniles spend their time nursing, playing, learning to hunt, or practicing sexual behaviors. When young males reach sexual maturity they are forced out of maternity pods and band together with other males. Males will associate with pods of females to reproduce, but after doing so they will leave to search for other females. Delphinids often exhibit playful behaviors that serve no apparent purpose besides enrichment. Such behaviors include riding the wakes of boats, surfing waves, and playing with objects in the water.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• motile motile
• nomadic nomadic
• social social
• dominance hierarchies dominance hierarchies

Communication and Perception

Species in the family Delphinidae have relatively poor vision, and instead rely primarily on acoustic stimuli to communicate and perceive their environment. Oceanic dolphins produce high pitch social calls and use echolocation while foraging for prey. They have a fatty organ in their foreheads, called a melon. The melon acts as a lens to focus sound waves towards their ear bones, which helps them detect and determine the direction of acoustic stimuli. Their teeth also direct vibrations through their jaws to their ear bones. Delphinids communicate with other members of their pod to coordinate foraging efforts. They communicate using social calls, body movements, and by blowing air through their blowholes. Delphinid communication is poorly studied. Their social calls are numerous and complex, and there are a wide range of behaviors that are not thoroughly understood. Oceanic dolphins also use physical communication with potential mates or with their offspring.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• echolocation echolocation
• chemical chemical

Food Habits

Oceanic dolphins are carnivores, eating mostly fish and squid. Larger species such as orcas ( Orcinus orca ) also hunt larger prey such as penguins (family Spheniscidae ), earless seals ( Phocidae ), eared seals (family Otariidae ), walruses (family Otobenidae ), and smaller delphinids. Specific prey species vary between species in the family Delphinidae depending on geographic location.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • molluscivore molluscivore

Predation

Delphinids are apex predators, but smaller species are prone to predation by large sharks and other, larger delphinids. Oceanic dolphins avoid predation by living in social groups, called pods. When threatened by predators, members of a pod will group together and protect young or sick individuals. They have also been reported to attack potential predators by ramming into them. Delphinids also exhibit countershading (darker dorsal coloration and lighter ventral coloration), which makes them more difficult to detect visually.

Ecosystem Roles

Oceanic dolphins are apex predators in the ecosystems they inhabit. They also serve as prey for other apex predators, such as sharks and larger delphinids. Beyond their roles as predator and prey, relatively little is understood about their relationships with other organisms in their communities.

Economic Importance for Humans: Positive

Oceanic dolphins are economically important for many coastal communities. Delphinids and other groups of whales are an important source of ecotourism. For example, whale watching tours and aquarium shows attract millions of customers every year. There are also a few countries, such as Iceland, where native communities rely on whaling for meat. Oceanic dolphins and other whales play important roles in marine ecosystems and their presence benefits fishery yields.

• Positive Impacts
• food food
• ecotourism ecotourism
• research and education

Economic Importance for Humans: Negative

There are no known negative economic impacts associated with delphinids.

Conservation Status

Many species in the family Delphinidae are poorly studied and more research is needed to determine their conservation status. Hector's dolphins ( Cephalorhynchus hectori ) are considered endangered and Atlantic humpback dolphins ( Sousa teuszii ) are considered critically endangered on the IUCN Red List. Species such as orcas ( Orcinus orca ) and common bottlenose dolphins ( Tursiops truncatus ) are currently considered to have healthy population levels.

Additional Links

Encyclopedia of Life

Contributors

Caroline Smith (author), Colorado State University, Galen Burrell (editor), Special Projects.

References

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