Monday, February 14. 2011
With today being "Valentine's Day" it's an appropriate time to introduce you to a group of dolphins who are in dire need of some love and protection ... the River dolphins! Over the next few weeks we'll be looking at the different species in more detail and telling you about some of the research being undertaken to help us learn more about these animals that really need our help but to begin with, here's a quick overview of the species considered "riverine".
Protecting River dolphins
There is a small, unusual group of dolphins that live exclusively in fresh water rivers and lakes. Unfortunately, these special dolphins are among the most endangered mammals on earth. Tragically, it is a river dolphin that is the only cetacean to have gone extinct in modern times at the hands of man. In 2007, the Chinese river dolphin, or baiji, was declared extinct. The baiji’s only home was the Yangtze River. Their demise was entirely due to the human impacts of habitat destruction and bycatch in fishing equipment.
River dolphins are emblematic species for rivers. This is because saving river dolphins means saving rivers. If river dolphins and their river homes can be protected, hundreds of thousands of other species, not to mention the local people dependent on supplies of fresh water, will also benefit.
Losing the baiji
is a shocking early warning sign of the probable outcome for the surviving river dolphin species. Put very simply, if we do not do more to protect river dolphins and their river habitats, we will lose them forever. River resources, like all natural resources, are not inexhaustible and many impacts are not reversible. Once flagship species such as river dolphins start to disappear from stretches of river, it may already be too late to make amends.
Where are river dolphins found?
Today, river dolphins survive in two areas of the world; South America and Asia.
In South America, the Amazon river dolphin (also known as ‘boto’, ‘bouto’, ‘bufeo’ and ‘Inia’) and the tucuxi (sotalia) live in the Amazon and Orinoco river basins of South America.
In Asia, the Ganges river dolphin (susu) lives in the Ganges river basin of Nepal, India and Bangladesh, and the Indus river dolphin (bhulan) lives in the Indus river basin of Pakistan.
In addition, there are other dolphins who are not members of the river dolphin family living in freshwater habitats. These include small and isolated fresh water populations of Irrawaddy dolphins living in rivers and lakes of Cambodia, Laos, India, Vietnam, Thailand and Myanmar. The finless porpoise also inhabits freshwater regions of the Yangtze River in China.
Why are river dolphins in so much trouble??
River dolphins are particularly vulnerable because they are restricted to fresh water (rather than bigger areas of ocean) and are found in naturally low population numbers. They are extremely vulnerable to direct threats related to human activity and resource use. Many of the rivers they inhabit have become extremely important resources for large human populations. River dolphins therefore suffer majorly from human vs. wildlife conflicts.
Meet the River Dolphins
There are four families of river dolphin:
1. Lipotes family
or Chinese river dolphin (Lipotes vexillifer
) was the sole member of the Lipotes family and lived in the Yangzte River of China for some 20 million years. It is now extinct and tragically, this means an entire family of mammals is now gone forever. The baiji’s
extinction is entirely due to human impacts; such as the ongoing degradation of its habitat, heavy ship traffic, pollution, human land uses as well as unsustainable fisheries and bycatch. It is the first large mammal to be driven to extinction by people in recent times. The baiji’s
demise can only mean that the Yangzte River ecosystem and the people living there are in very serious trouble. The Yangtze River basin has a population of approximately 400 million people, equal to about one in 17 of all people on the planet! Sadly the baiji’s story is an early-warning sign of more extinction to come; unless action is taken to stop history repeating itself both in China, where the finless porpoise can still be found in the Yangzte River, and in other parts of the world.
2. Inia family
The Inia family includes the boto
, or Amazon river dolphin (Inia geoffrensis
), and the Bolivian river dolphin (Inia boliviensis
), which both call South America home. The boto
lives in the Amazon, Orinoco and Araguaia/Tocantins river systems of Peru, Colombia, Venezuela, Brazil, Ecuador and Guayana; whereas the Bolivian river dolphin is only found in Bolivia! Botos
are the largest of all river dolphins (1.8 – 2.5m long). They have a hump on their back, rather than a well-defined dorsal fin, and a long narrow beak lined with teeth. Botos
have 25-30 peg-like front teeth for catching prey and molars for crushing their food at the back of their mouths. They use echolocation to hunt and catch their prey and mainly eat fish (particularly catfish) and crustaceans. Their flexible neck vertebrae, unique to river dolphins, means they can move their necks up and down and from side to side. This gives them much greater maneuverability in the flooded forest. This maneuverability enables them to swim amongst trees and bushes that are underwater during the rainy season. They navigate over and under roots and branches, hunting and catching the fish that feed from seeds and berries. They are often seen swimming upside down, which may seem peculiar, however it is thought to be down to their overly chubby cheeks obstructing their downward vision! Botos
are well-known for their unusual pink colouration. It is a beautiful and striking contrast to the often brownish coloured river water and green forest. The calves are usually born with greyish skin and most then become pinker with age. Adults can, however, vary in colour from grey to pink. The pinkness is thought to be due the presence of lots of blood vessels close to the surface of the skin but the reasons for adult colour variation are unknown.
The Bolivian river dolphin (Inia. g. boliviensis
) lives only in Bolivia. An extensive drought in the Madeira region of Brazil between 100 and 500 thousand years ago resulted in Bolivian botos becoming separated from other botos by newly created and impassable rapids. The botos in Bolivia have therefore been isolated from other botos for such an extended period that they are now considered genetically distinct and are in the process of being classified as a different species of river dolphin. This clearly has huge consequences for river dolphin conservation. Protecting botos in Bolivia becomes that much more important as it means protecting an entire species.
3. Platanista family
The Platanista family includes the Ganges river dolphin
of Nepal, India and Bangladesh, and the Indus river dolphin
of Pakistan. There is an ongoing debate amongst scientists about whether these dolphins are separate species, or subspecies of the same species. One thing is certain, the Ganges and Indus River Dolphins are completely separated geographically. They are, however, identical in appearance. The body is a grey -brownish colour and stocky. They have a small triangular lump as opposed to a dorsal fin. Their flippers and tail are large in relation to the body size, which is about 2 to 2.2 meters in males and larger (2.4 to 2.6 m) in females. Their long, slender beaks characteristic of all river dolphins, are used to catch fast moving prey. These river dolphins do not have a lens in their eyes and so they are blind, although they can probably detect the intensity and direction of light. Instead of relying on sight, they use echolocation to hunt and navigate in the murky waters they inhabit. They feed on a variety of fish, including carp and catfish and shrimps. Both Ganges and Indus river dolphins
are usually encountered in ones and twos or in loose aggregations; they do not form tight, obviously interacting groups.
The Ganges River dolphin
or susu, was formerly distributed throughout the Ganges-Brahmaputra river system of Bangladesh, India and Nepal, and possibly Bhutan. Although it still has a fairly extensive range, its distribution has contracted, and its abundance has declined dramatically in some areas. Currently it is found in the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Bangladesh and India. A few individuals survive in Nepal in the Karnali River and possibly the Sapta Kosi River. Its habitat is severely fragmented, and additional barrages continue to be built. Sadly, it is almost certainly declining in numbers.
The Indus river dolphin
or bhulan is found only in the Indus river of Pakistan. It is classed as endangered by IUCN. It is one of the world’s rarest animals and is the rarest river dolphin (now that the baiji is extinct). Estimated overall numbers of animals surviving maybe as few as 1100 individuals and numbers are thought to be still declining. Historically it ranged from the Indus delta upstream to the Himalayan foothills. Currently the distribution of the Indus River dolphin is severely fragmented and dramatically reduced in extent. An estimated 99% of the Indus River dolphin population occurs in only 690 linear km (430 mile) segment of the river. Currently the Indus River dolphin is limited to three subpopulations in the Indus mainstream located between the Chashma and Taunsa, Taunsa and Guddu, and Guddu and Sukkur Barrages. The main reason for the decline of the Indus River dolphin was the construction of numerous dams and barrages, starting in the 1930s, that have fragmented the population and reduced the amount of available habitat. Another severe threat to the survival of the Indus River Dolphin is probably the increasing withdrawal of water used for the irrigation of farmlands around the river. Dolphins no longer occur in the lower reaches of the Indus because upstream water extraction leaves downstream channels virtually dry for several months each year.
4. Pontoporia family
or La Plata River Dolphin (Pontoporia blainvillei) is scientifically grouped in the river dolphin family (its neck vertebrae are not fused and the beak is very long). However, the franciscana is not restricted to fresh water rivers and lakes; it is found in coastal Atlantic waters and estuaries of southeastern South America (Uraguay, Argentina and Brazil). Whilst some members of the species do spend portions of their lives outside of river systems, there are many individuals who live their entire lives within rivers, never venturing into the ocean proper. It is one of the smallest cetaceans and has the longest beak relative to its body size of all cetaceans. In fact the beak can account for almost 15% of its entire body length! Due to similar appearances it can be confused with the tucuxi (see below) but it is mainly their longer beak that sets them apart.
In common with other members of the river dolphin group, the franciscana
has a restricted distribution. Gillnet fishing also has a two-fold impact on franciscanas
. Bycatch rates through entanglement in gillnets are high but the damaging effects of trawling for franciscana
prey species has also had a major impact on their habitat. The combination of these factors poses a very serious threat to the future of the franciscana
5. Other Fresh Water Dolphins
There are a number of dolphin species that live permanently in freshwater rivers but are not scientifically related to the river dolphin family. These are oceanic dolphin species that have populations which solely live in fresh water – the tucuxi or sotalia, Irrawaddy dolphin and finless porpoise:
Tucuxi or Sotalia (Sotalia fluviatalis)
can inhabit both marine and freshwater systems. They are classed as members of the oceanic dolphin family (Delphinidae) and look very much like mini bottlenose dolphins. The fresh water sotalia
live in South American rivers and lakes of the Amazon and Orinoco basins. They exist along much the length of the Amazon River and many of its tributaries, and are found in Brazil, Peru, Colombia, and Ecuador. Amazon river dolphins
can often be found alongside each other in South American rivers and lakes. However, unlike the boto
do not enter the flooded forest during high water. They prefer to remain in the deeper water channels and lakes. The two species are not closely related genetically. Although the ranges of the marine and freshwater dolphins overlap, they are thought to be distinct species and may soon become classified separately. Whilst appearing almost identical, size can be a key distinguishing feature between the two with individuals in the marine population being up to 30% larger than their freshwater counterparts.
Irrawaddy Dolphins (Orcaella brevirostris)
are largely oceanic dolphins that live in brackish water in river mouths, estuaries and coastal areas. However, there are a few established sub-populations of Irrawaddy dolphins entirely restricted to freshwater. They live in Asian rivers, including the Mekong in Laos and Cambodia, the Ayeyarwady River in Myanmar, the Mahakam River in Indonesia, Songkla Lake in Thailand and Chilka Lake in India. All of these populations, without exception, are very small and threatened with extinction.
are grey, they have a large melon and a blunt, rounded head, and the beak is indistinct. They have a small, blunt, triangular-shaped dorsal fin. The flippers are long and broad. Adults grow up to 2.3m (8ft) long and weigh 130kg (287lb) kg. Threats include bycatch in monofilament gillnets used extensively in all rivers. Capture for captive display in aquariums in Asia is also a major threat.
Finless Porpoise (Neophocaena phocaenoides)
The finless porpoise
lives in the coastal waters of Asia. They are most commonly found in the waters around India, China, Indonesia, Bangladesh and Japan. There is also a unique fresh water population (Neophocaena phocaenoides asiaeorientalis
) surviving in the Yangtze River, China. The current population is just a fraction of its historical levels. A 2006 expedition estimated that fewer than 400 porpoises survived in the Yangtze River and it is heading for extinction. The same factors that recently drove the baiji
to extinction are leading to the demise of the finless porpoise
; habitat degradation and bycatch.