Last modified: Sunday May 20th, 2001

Working with dolphins: a challenge!

Nederlandse versie

Interest in dolphins goes back a long way, all the way to the ancient Greeks. These mysterious aquatic creatures filled people with awe and often they were treated as gods. Aristotle classified them as fish, since they lived in water and had no fur. Only fairly recently, people realized that dolphins are mammals, instead of fish. They have lungs to breathe with, are warm-blooded and give birth to live young that are nursed.

Before getting into the care of dolphins in captivity, I'd like to give some information about the biology of dolphins, especially about the best-known species, the bottlenose dolphin, Tursiops truncatus. The bottlenose dolphin can be found in waters all over the world. There are some differences between populations, but in general the bottlenose dolphin is considered to be a single species. Most of the bottlenose dolphins that you will encounter in European oceanaria originate from the Gulf of Mexico. Those dolphins usually are no larger than about 3 meters. In the North Sea for instance, bottlenose dolphins can grow up to 4 meters. Usually bottlenose dolphins live in small groups of 4 to 6 animals. These pods can aggregate into larger herds, but usually such aggregarions are only temporary. They hunt for fish, their main food, in groups. The composition of their diet varies with location and season.

How old a dolphin can become is not known exactly, but the maximum age is probably around 35 to 40 years. Females become sexually mature at 6 to 12 years of age. Males mature at 10 to 12 years. The gestation period is long: about 12 months. Twins are very rare. The calf is born underwater, usually tail first. But head first births do occur and can be successful. Once the umbilical cord breaks, the calf swims to the surface for its first breath. Occasionally the mother or another dolphin helps the calf, but usually this is not necessary. After birth, the calf swims in its mother's slip stream by positioning itself near the dorsal fin. This way, the calf can keep up with its mother without having to use a lot of energy. Shortly after birth, the calf starts nursing. The female's mammary glands are located next to her genital slit. The milk, which is very rich in fat, is more or less squirted into the calf's mouth. The calf continues to nurse until it is about 9 to 12 months old. Then it slowly starts eating fish.

What does this mean for the husbandry of dolphins in captivity? As mentioned, a dolphin's diet consists mainly of fish. They eat a wide variety of fish. They often do need some time to get used to new species. The first thing a dolphin, collected from the wild, needs to get used to is eating dead fish. Maintaining live fish as a food supply is not really practical. Sometimes, they get used to it almost immediately, but it can take up to several weeks before they reliably eat dead fish. The most common food fish in captivity is herring, but other species are used as well, including mackerel, sprat, whiting, capelin and squid. It is essential that the fish is of a high quality with a minimum of pollutants. Depending on the diet composition and the caloric value of the fish, a dolphin eats 6 to 9 kilos a day. Nursing females can eat double that amount. When good quality fish is used, vitamin supplements are not necessary, except vitamin B1 supplements. Some fish species, like herring and sprat, contain the enzyme thiaminase, which breaks down vitamin B1. When the diet contains a lot of those species, vitamin B1 supplements are essential. Using expensive multi-vitamin supplements is not necessary when good quality food is used, but often these vitamins are given anyway, as a precaution.

A dolphin spends its whole life in water, so it is obvious that good water quality is of the utmost importance. Since dolphins are marine mammals, they need salt water. Seawater contains about 3.5% salt, so the salinity of the water for dolphin pools should be close to that. The water needs to be kept clean, so a water purification plant is an essential part of an oceanarium. Most dolphinaria use water purification techniques derived from swimming pool techniques. The water is filtered in large sand filters and is then disinfected with chlorine. When used properly, chlorination yields acceptable water quality. However, chlorination can lead to skin and breathing problems, since chlorination of salt water is difficult. Recent research in England has shown that toxic, irritating or even carcinogenic byproducts can be formed. For that reason, several parks have started looking into other water purification techniques. Often ozone is used, usually in combination with marginal chlorination. At the Delfinaario of Särkänniemi in Tampere, Finland, which was built in 1985, a totally different approach was taken. There the water is treated biologically, using techniques borrowed from wastewater and drinking water purification. Because this system retains most of its water, as opposed to chlorinated systems in which large amounts of water need to be replaced on a regular basis, it has been possible to maintain a water composition which is close to natural seawater. Seawater contains, apart from sodium chloride (kitchen salt), substantial amounts of calcium and magnesium salts and trace elements like zinc and copper. There are some indications that dolphins can absorb trace elements from the water. So it is important to add these elements to the water in order to create an optimal environment. Unfortunately it is not possible to convert existing water treatment plants to biological plants, but it is an option that should be considered for new facilities.

Note added after publication: the Zoo in Duisburg, Germany, has implemented a biological system for its new dolphin facility and the Dolfinarium in Harderwijk, the Netherlands has a biological purification system for its Dolphin Lagoon

Veera en Joona In the wild, dolphins spend a lot of time foraging. In captivity, they get their food without having to exert themselves. At first glance this looks like an ideal situation for the animals, but it isn't. Dolphins that are just being fed get bored. This can lead to stress, with obvious adverse effects. They can develop stomach ulcers and show aberant behavior, such as apathy, stereotyped behavior and aggression. This can be easily prevented by giving the animals something to do. Therefore people started training dolphins years ago. First, very basic operant conditioning techniques were used, with food reinforcement: when the dolphin performed a desired behavior, it was rewarded with fish. Already in the sixties, people noted that food was not a really strong motivator for dolphins. But it took several years before trainers started experimenting with other rewards and other reinforcement strategies. Especially within IMATA, the International Marine Animal Trainers Association, a lot of attention has been devoted to this aspect. The personality of individual dolphins plays a key role. This requires some more work from the trainers, since a trainer needs to know the likes and dislikes of each individual. But when you know the animals, you can easily reward them with a friendly voice, a favorite game or scratching or petting the dolphin. Training does not automatically mean that a dolphin has to do all kinds of circus-like tricks, although dolphins usually like to perform such behaviors for a change of pace during other tasks. Dolphins can be trained to co-operate in scientific research and this has helped expand our knowledge of these animals. Also, dolphins can be trained to co-operate in standard medical procedures. Usually, blood samples are taken from veins in the tail flukes. If you train a dolphin to present its tail and keep it still for a while, you can take blood samples regularly without having to restrain them. In a similar fashion dolphins can be trained for the collection of stomach, fecal and urine samples as well as for ultrasound examinations. This is important, since these techniques make it possible to detect and treat health problems early on, without any stress for the dolphin.

When a dolphin does not feel well, often it will stop eating. This requires immediate attention, since food is also the dolphin's only source of water. Seawater contains too much salt, so they cannot drink it. If they don't eat for a long period, there is a risk of dehydration, so a sick dolphin must be treated quickly and effectively. If the dolphin has been trained for husbandry procedures, and is used to rewards other than food, there is a fair chance that the animal can be examined and even treated without having to restrain it.

Dolphins are fascinating animals, which in captivity need a high quality environment, both physically and mentally. High quality food, clean water and behavioral challenges are essential. A dedicated training program which focuses on play and practical applications, such as husbandry behaviors, and which presents the animals with mental stimulation is paramount for the well-being of the dolphins.


Jaap van der Toorn is a biologist, specialized in marine mammals. From 1984 through 1987 he worked at the Delfinaario in Tampere, Finland, where he was responsible for the training and husbandry of the dolphins, the educational program and the operation and development of the biological water treatment system.


This paper was published as:
van der Toorn, J.D. 1988.
Werken met dolfijnen - Een uitdaging! De Harpij 7.4: 6-8
De Harpij is the quarterly journal of the Association for Zookeepers in the Netherlands and Belgium


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