From video films, dolphins in the Moray Firth certainly appeared to be attacking porpoises which may reveal a previously unsuspected dark side to their nature.

However, to date, no incidents have been reported of dolphins deliberately attacking people. Indeed the opposite is the case. There have been innumerable reports of dolphins saving people.

Nonetheless all those who swim with dolphins should be aware of the possible dangers. Dolphins can become extremely boisterous when playing with one another, and if a human joins in their games he/she may get injured.

Dolphins have to be conscious to breath. This means that they cannot go into a full deep sleep, because then they would suffocate. Dolphins have "solved" that by letting one half of their brain sleep at a time. Dolphins sleep about 8 hours a day in this fashion. REM (Rapid Eye Movement) sleep, usually associated with dreaming has been recorded only very rarely. Some scientists claim dolphins do not have REM sleep at all.

A dolphin's behaviour when sleeping/resting depends on the circumstances and possibly on individual preferences.

They can either: - swim slowly and surface every now and then for a breath - rest at the surface with their blowhole exposed - rest on the bottom (in shallow water) and rise to the surface every now and then to breath.

The short answer to this is that we do not know. There is no reliable method to measure intelligence in humans across cultures, so it is not surprising that comparing humans, dolphins, apes, dogs, etc. is impossible. There are some indications of their potential: they are fast learners and can generalise (which is also true of pigs). Also they can learn to understand complicated language-like commands (which is also true of the great apes).

Dolphins have brains as large as humans and have had them for millions of years longer than us. Many scientists agree that if they were not using their brains during this long evolutionary period, dolphins’ brains would have atrophied. Humans have used their brains to change their lifestyle and in doing so have changed the planet. In contrast, dolphins are in total harmony with their environment and probably use their brains to appreciate and enjoy their surroundings. This, some animal behaviourists argue, could make them more intelligent than us - but in a completely different way.

Dolphins communicate mainly by means of sounds. These sounds include whistles, but also so-called pulsed sounds, which are often described as squawks, barks, rasps, etc. But they also use breaching (jumping and falling back into the water with a loud splash) and pectoral fin (or flipper) and tail (or fluke) slaps (hitting the flipper or fluke on the water surface). Body posturing and jaw popping also have a role in communication. As for language, we do not know if they have one. Several studies have demonstrated that dolphins can understand a structured language like ours. This same has been demonstrated for a number of other animal species as well (gorilla, bonobo, California sea lion, parrot). Some studies also indicate that dolphin vocalisations are complex enough to support some form of language. However, to date it has not been demonstrated yet that they can undoubtedly communicate among themselves.

On the basis that dolphins have large brains and their primary sense is acoustic, Dr. Horace Dobbs has speculated that dolphins send holographic sound images to one another. In his series of books about a fictional dolphin named Dilo, author Horace Dobbs refers to Dilo’s Magic Sound. Thus, when Dilo’s Mother investigates a lobster with her sonar, she mimics the echo when informing her offspring about the lobster. In this way she can pass real information instead of using words, which are an abstraction. Thus Dr. Dobbs argues that dolphins have gone beyond language and could be far more advanced than humans when it comes to sonic communication.

Dolphins (and other toothed whales) can produce high-pitched clicks. When these clicks hit an object, some of the sound will echo back to the "sender". By listening to the echo and interpreting the time it took before the echo came back, the dolphin estimate the distance of the object. (That's why sonar is also called echo-location: with information from the echoes, a dolphin can locate an object). Depending on the material the object is made of, part of the sound may penetrate into the object and reflect off internal structure. If the object is a fish, some sound will reflect off the skin, some off the bones and internal organs. So one click can result in a number of (weaker) echoes. This will give the dolphin some information about the structure and size of the fish.

By moving its head (thereby aiming the clicks at other parts of the fish) the dolphin can get more information on other parts of the fish. It is like a medical ultrasound probe, but the results are far less clear. A medical probe moves back and forth very rapidly, much faster than a dolphin can move its head. Also the frequency of the sounds of the medical probe is much higher than a dolphin's sonar. Therefore the level of detail the echoes can provide is much higher in the medical probe.

The short answer is: yes, they can. Just like people can visualise an object by just touching it, dolphins can get an idea of what an object looks like by scanning it with their sonar. They can also identify objects with their sonar that they have only been able to see. If they form a visual picture from the sonar information (visualisation) or form an acoustical picture from visual information is still unresolved.

This capability is called cross-modal transfer and it has been demonstrated in only a few animal species so far: the bottlenose dolphin and the California sea lion.

Bottlenose dolphins eat several kinds of fish (including mullet, mackerel, herring, cod) and squid. The composition of their diet depends very much on what is available in the area they live in and also on the season.

The amount of fish they eat depends on the fish species they are feeding on: mackerel and herring have a very high fat content and consequently have a high caloric value, whereas squid has a very low caloric value, so to get the same energy intake (calories) they will need to eat much more if they feed on squid than if they feed on mackerel or herring.

On average an adult dolphin will eat 4-9% of its body weight in fish, so a 250 kg (550 lb) dolphin will eat 10-22.5 kg (22-50 lb) fish per day

The maximum age for bottlenose dolphins is between 40 and 50 years.

The average age a dolphin can get (the life expectancy) is about 25 years.

There is, however, anecdotal evidence, which indicates that dolphins can live longer than estimated if death by human interference is eliminated from calculations.

A study, comparing the survival of dolphins in captivity from 1940 - 1992, showed no significant difference between the captive population and the wild population. In captivity dolphins have reached ages over 40 years.

However, this conclusion could be misleading as many of the early dolphinariums did not record deaths and secretly replaced dolphins if one died, giving the replacement dolphin the same name as its predecessor.

IDW do not approve of keeping dolphins in captivity

The earliest recognisable cetaceans lived about 50 million years ago. These evolved from large land mammals, some of which were carnivorous, some herbivorous.

The earliest dolphins appeared in the late Miocene period, some 11 million years ago. The land animals that are closest to whales and dolphins are the Ungulates (hoofed animals).

When swimming, boating or snorkeling in certain areas you can encounter wild dolphins. In the US it is illegal to directly approach dolphins. If dolphins come towards you and choose to interact, that is allowed. In several areas there are boat operators that can take you to areas where there is a good chance to encounter dolphins (Florida, Bahamas).

A note of warning: there have been operators that have tried to lure dolphins by feeding them. This is illegal in the US and is highly undesirable, because it changes the dolphins' behaviour. There are also operators offering bird-feeding tours. These bird feedings take place in areas frequented by dolphins and are an attempt to circumvent the dolphin-feeding ban. Do not use these operators.

If a single whale or dolphin strands, it usually is a very sick (and exhausted) animal. Such an animal often has some infections (pneumonia is almost always one of them) and a lot of parasites (worms in the nasal passages are very common). Sometimes these animals can be rehabilitated, but often they are so sick they won't make it. Some species of whales and dolphins occasionally strand in groups. A stranding of two or more animals is usually called a mass stranding. There are a number of theories that try to explain the occurrence of mass strandings. No theory can adequately explain all of them. In some cases it will be a combination of causes. The most common explanations are: - deep-water animals (the species that most often are the victim of mass strandings) cannot "see" a sloping sandy beach properly with its sonar. They detect the beach only when they are almost stranded already and they will panic and run aground.

Whales and dolphins may be navigating by the earth's magnetic field, if the magnetic field is disturbed the animals get lost and may run into a beach. In some highly social species, the group leader may be sick and wash ashore. The other members try to stay close and may strand with the group leader.

The deepest dive ever recorded for a bottlenose dolphin was a 300 meters (990 feet). This was accomplished by Tuffy, a dolphin trained by the US Navy.

Most likely dolphins do not dive very deep though. Many bottlenose dolphins live in fairly shallow water. In the Sarasota Bay area, the dolphins spend a considerable time in waters that are less than 2 meters (7 feet) deep.

Other whale and dolphin species are able to dive to much greater depths even. The pilot whale can dive to at least 600 meters (2000 feet) and a sperm whale has been found entangled in a cable at more that 900 meters (500 fathoms) depth. Recent studies on the behaviour of belugas have revealed that they regularly dive to depths of 800 meters. The deepest dive recorded of a beluga was to 1250 meters.

The dolphin's fast cruising speed (a travelling speed they can maintain for quite a while) is about 6-7 knots. . They can reach speeds of up to 9.3 knots while travelling in this fashion. When they move faster, they will start jumping clear of the water (porpoising). They are actually saving energy by jumping. When chased by a speedboat, dolphins have been clocked at speeds of 14.6 knots, which they maintained for about 1500 meters, leaping constantly.

Studies have shown, that the most efficient travelling speed for dolphins is between 3.3 to 4.5 knots. There have been reports of dolphins travelling at much higher speeds, but these refer to dolphins being pushed along by the bow wave of a speeding boat. They were getting a free ride (their speed relative to the surrounding water was low). It is possible that dolphins can reach speeds over 15 knots during very short bursts (like in preparation for a high jump), but they can't maintain that speed.

Whales and dolphins can be found in almost every sea and ocean, from the Arctic Ocean, through the tropics all the way to the Antarctic. Each species however has its own preferred type of habitat.

Some live in cold water only, others in tropical oceans only.

There are also species that can be found in a large variety of environments, like the bottlenose dolphins, killer whales and sperm whales. The map shows documented sightings of bottle nosed dolphins in dark blue.

There are a number of dolphin species that live in fresh water.

They all belong to the river dolphin families (shown here is a pink Amazon river dolphin).

There is one species that can be found both in fresh water (the Amazon river) and in coastal sea waters.

In general, salt-water species don't do well in fresh water. They can survive for some time, but they will be come exhausted, since they have less buoyancy in fresh water, and after a while their skin will start to slough (like our own skin after spending a long time in the bathtub)

Most dolphins live in the ocean and the ocean water is too salty for them to drink. If they drank sea water, they would actually use more water trying to get rid of the salt than they drank in the first place.

Most of their water they get from their food (fish and squid). Also, when they metabolise (burn) their fat, water is released in the process.

Their kidneys are also adapted to retaining as much water as possible. Although they live in water, they have to live as desert animals, since they have no direct source of drinkable water.

Click here to see larger image

Horace Dobbs has written a series of books about a fictional dolphin, named Dilo, for children.

The books also appeal to adults because they are written from a dolphin’s viewpoint and give a wonderful insight into the undersea world as perceived by both humans and dolphins. They are available from the on-line Dolphin Shop.

There are 33 different types of marine dolphins and 4 types of river dolphins

Closely related families are the white whales with 2 species

Dolphins and porpoises belong to different whale families.

The most obvious differences are: - dolphins have a hook-shaped dorsal fin, whereas porpoises have a triangular dorsal fin. - dolphins have conical teeth; the teeth of porpoises are spatula shaped. - most dolphin species have a distinct beak, porpoises don't, giving their head a more rounded, blunt shape

For most species, the answer is probably "No", although it is very difficult to get a good estimate of the size of populations on these water living creatures.
A number of species ARE endangered: the Indus river dolphin, the baiji (there are only about 100 left), the vaquita, the northern right whale and the blue whale.

Because more people are looking out for dolphins and recording their sightings, it appears that there are more dolphins around.

However, the depletion of fish stocks and the accidental capture of dolphins is undoubtedly leading to an overall decline in dolphin populations. It is estimated that dolphins will be virtually eliminated from the North Sea if pair trawling, which is killing hundreds and possibly thousands of dolphins, is allowed to continue.