THE BOTTLE-NOSED DOLPHIN Tursiops truncatus

Recognition

Short but distinct beak, tall dorsal fin, centrally placed.
Colour: darker, grey to brown, dorsally, with lighter flanks and even paler belly.
Maximum length: in the region of 4.0 m (males are larger than females).
Maximum weight: some 275 kg.

General Ecology

Bottle-nosed dolphins occur worldwide, except for polar regions. Two forms (or "ecotypes") are recognised: a generally larger offshore form and a smaller coastal form. Indeed, whether the widespread Bottle-nosed dolphin is really just one species is presently being debated. They are the most studied and familiar of all the dolphins but relatively little is known about them in the UK (most information is available from studies in the US). Bottle-nosed dolphins can occur anywhere on the British coastline. Historically they have been closely associated with estuaries, but present populations are believed to be reduced. "Resident" populations exist in the Moray Firth in Scotland and Cardigan Bay in Wales. Bottle-nosed dolphins returned to the Cornish coastline in 1991 after an absence of some years and this may prove to be another resident group. The species is capable of a wide range of behaviour making it difficult to generalise about them. They are highly social animals, usually seen inshore in groups smaller than ten individuals, but far larger congregations are sometimes reported. Occasionally solitary bottle-nosed dolphins are reported, which seem to shun their own kind and, instead, favour contact with humankind.

The family groups are usually based around adult females. Mother-calf bonding can last many years and form the focus of family groups. Gestation lasts for twelve months and, once mature, females may have a single calf every second or third year. Females, other than the mother, may assist in caring for the calf. Adult males may occasionally join such families but, more frequently, may be seen in bachelor gatherings. Behaviour may also change seasonally but, as with all other matters relating to UK dolphins, research into this is only at a very early stage.

This species feeds on a wide variety of fish and invertebrates, including squid, and they sometimes feed cooperatively herding their prey until it is concentrated near the water surface.

Conservation

Bottle-nosed dolphins and other inshore cetaceans are protected by law in UK waters and may not be intentionally killed, injured, captured or harassed. However, they face a number of modern threats. The most important of these are pollution, accidental capture in fishing nets, disturbance and very occasionally intentional killing. In the Faroes, small whales and dolphins are driven ashore and killed in a "drive fishery". The ranges of UK dolphins are not yet clear and it is possible that dolphins from the UK are caught in this activity. Like some other dolphin species, bottle-noses regularly "bowride" in front of boats. This makes them especially vulnerable to being shot or harpooned and, as such bodies are unlikely to be recovered, the frequency of such activities cannot be estimated. Similarly, animals caught accidentally in fishing nets are not presently monitored, but this may be more significant for offshore dolphins.

Dolphins in the UK have also been found to contain high concentrations of certain pollutants in their tissues. Heavy metals, including mercury, and organochlorines, including PCBs and DDT, are of particular concern. Such compounds are associated with a range of adverse effects in mammalian and other species. Toothed cetaceans are at the top of the food chain and therefore tend to accumulate very high concentrations of these pollutants. It has been found that many chemicals of concern are passed from mother to calf through the placenta and in mothers' milk. This is likely to cause problems with development, reproduction and immunity. Pollution, overfishing and other human activities which degrade marine habitats may also affect dolphins indirectly by reducing the availability of their prey. Bottle-nosed dolphin habitats are poorly understood but it is likely that the survival and success of these animals are favoured by certain conditions. Important breeding, feeding and calving grounds may become less suitable for dolphins if they are subject to noise and other disturbance. Whilst bottle-nosed dolphins are regarded as a species that is highly tolerant of many of man's marine activities, there is some evidence that they may move away from disturbed areas.

Frequent Questions

Are dolphins intelligent?
Bottle-nosed dolphin intelligence has evolved for an entirely marine-based way of life. They have a complex communication system and use a range of well developed senses, including sonar, to find their way in their environment. Their social systems are also well developed and, like other aspects of their behaviour, are very flexible. These facets and their ability to learn, indicate high intelligence, but it remains difficult to compare this with our own.

Should dolphins be kept in captivity?
Public concern at the behavioural and physiological disorders that develop in captive dolphins, has led to the closure of all dolphinaria in the UK and in many other parts of the world. A more satisfactory way to encounter dolphins (for both themselves and observers who wish to appreciate their normal behaviour) is to see them in the wild. A dolphin and whale watching industry is developing world-wide and, with proper care and consideration, they can be seen in their natural environment.

Do dolphins have healing powers?
Many claims have been made about the "magical" healing power of dolphins. These cannot be scientifically validated. However, encounters with these large, intelligent and, usually, surprisingly friendly wild animals, are frequently described as exhilarating and inspiring; perhaps this is at least part of their "magic".

Further information

 

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