Dolphins are among the smallest of cetaceans - whales, dolphins and porpoises. The greatest number of dolphin species belongs to the largest cetacean family, the Delphinidae that comprise those species referred to widely as ocean dolphins. Many species of dolphins are streamlined in shape and have a prominent dorsal fin, are capable of great speed in the water and exhibit spectacular acrobatics. There are some species that lack a dorsal fin but the majority have a dorsal fin and it is situated midway down the back. Most species of dolphin have a head that tapers into a distinct beak with varying numbers of conical, sharp teeth in both the upper and lower jaw with some exceptions. Many species of dolphins are social and may congregate in large numbers feeding on a large variety of fish, squid and other marine animals. Systematists have long disagreed on the classification of the ocean dolphin family, Delphinidae, but current thinking is that there are six subfamilies with a worldwide coverage from tropical waters to the sub polar regions and from shallow coastal regions to the deepest part of the oceans. They vary from bold colouration to more muted tones.
This single genus group of small coastal dolphins is found in temperate seas of the Southern Hemisphere. They have a very short beak and their dorsal fins tend to be more rounded or triangular rather than falcate. The genus Cephalorhynchus includes Commerson's Dolphin, the Chilean Dolphin, Heaviside's Dolphin and the diminutive and rare Hector's Dolphin. Distinctly limited in the respective ranges and in numbers these small dolphins are the subjects of much needed conservation effort.
This group usually includes the three genera, which contain the Rough-toothed Dolphin, the Tucuxi and the Hump-backed Dolphins. The first two species reside in their own genera, Steno and Sotalia respectively. The Hump-backed Dolphins are under scrutiny with regard their unresolved taxonomy - it is unclear how many species comprise the genus Sousa, one or three.
This is the largest subfamily, which contains the genera that are all marine species. These are Tursiops, the Bottlenose Dolphin, Stenella, the Spotted, Striped and Spinner Dolphins, Lagenorhynchus "lags", Delphinus, the Common Dolphins and Grampus, Risso's Dolphin.
This includes the two Right Whale Dolphins in the genus Lissodelphis. Differentiated from the other delphinids through the lack of any dorsal fin and with their very streamlined bodies they are frequently referred to as eel-like.
This includes the two Pilot Whales in the genus Globicephala and other genera Orcinus, (Killer Whale) Pseudorca, (False Killer Whale) Feresa (Pygmy Killer Whale) and Peponocephala (Melon Headed Whale). These genera include the so-called "blackfish" and although referred to as whales include the largest members of the dolphin family, Delphinidae.
This contains only one member, the endangered Irrawaddy Dolphin found in the river systems and coastal waters of Southeast Asia and Northern Australia. It's distinctive appearance with no beak and pale grey colouration distinguishes it from other dolphins within the family Delphinidae.
There have been significant increases over recent years in the numbers of sightings of different species of dolphins around Ireland with at least seven of the more than 30 known species having been recorded in the waters of the Eastern Atlantic, adjacent to Ireland.
Difference Between Dolphins and Porpoises
The word porpoise has often been used colloquially to describe porpoises, dolphins and in some cases larger whales. However, the family Phocoenidae are very different from dolphins in addition to being the smallest family of the order Cetacea. The difference between dolphins and porpoises is clear in that members of this family have small flippers, lack the prominent beak associated with many dolphins and have a more triangular dorsal fin rather than falcate. The teeth of porpoises are chisel shaped rather than conical as they are in most dolphins, and many species of porpoise frequent inshore, comparatively shallow water. Much of the difference between dolphins and porpoises is clearly identifiable in the field along with certain behavioural differences.
Dolphins Porpoises Differences
Of the six members of this family the shy rather cryptic Harbour Porpoise is the species that frequents the waters off West Cork. Porpoises are regularly seen during our whale and dolphin watching tours but they are shy and retiring in comparison to Common Dolphins. Porpoises in Ireland largely avoid contact with people and boats. Easily identifiable at sea, the main dolphins porpoises differences being that porpoises do not exhibit the clearly defined beak so characteristic of many dolphin species and they have a low triangular dorsal fin situated midway down the back. Throughout their range in Ireland by far the greatest threat to the Harbour Porpoise is bycatch - the accidental killing associated with marine trawl fisheries and bottom set gill nets. This has led many nations to classify this species "endangered" and render it special status. The carnage still continues however, leading to a significant reduction in population numbers around the Irish coast where they are seen in small family groups of up to five or six animals or more.
© Whale Watch West Cork Ireland 2005-2009
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Click on images for larger view:
Common Dolphin Reflections
Classic Bottlenose Dolphin
Risso's Dolphin with Scarring
Did you know...?
Proposals tabled by the United Nations and the North East Atlantic Fisheries Commission to put in place lasting protection for deep sea habitats and sea mounts has recently been scuppered by the pirate whaling nation Iceland. Talks to introduce a moratorium on unregulated deep water bottom trawling, a practice which is incredibly damaging to the deep sea marine environment, have recently been taking place. Even nations such as Japan, Canada and Spain, not known for their enlightened conservation policies, were prepared to accept a compromise which would have lead to a degree of protection for deep sea environments, especially cold water corals and sea mounts. Iceland however, was the only country to block the consensus that could have been reached and push for a continued destruction of deepwater marine habitats through bottom trawling. Habitats that harbour fish like the Orange Roughy which are believed to live as long as 200 years. The deep sea marine environment is very easily damaged by activities such as bottom trawling and some habitats may never recover. The call for a moratorium on deep water trawling has been supported by a recent study published in the acclaimed journal Science, that if we do not substantially change the way in which we manage our oceans then we may see a collapse of many commercial fisheries around the globe as early as 2048.