Dolphins in the North Sea
You wouldn't think so, but there are hundreds of thousands of porpoises and thousands of dolphins swimming in the southern North Sea. There used to be a lot of bottlenose dolphins as well, but now you see white-beaked dolphins more often. Every once in awhile, a short-beaked common dolphin or a white-sided dolphin is spotted or caught. Even more rare are Risso's dolphins, striped dolphins, orcas or pilot whales. Beaked whales form a separate group and include the bottlenose whale. These are ocean animals, which occasionally swim into the North Sea.
On Texel
At Ecomare, you can see bones and models of most of the dolphin species found in the North Sea. Dolphins and porpoises sometimes wash ashore on Texel. Porpoises are found the most but occasionally other species of dolphins are also seen or found dead, such as the white-beaked dolphin, the bottlenose dolphin and the common dolphin.
- Not see but hear
- Bottlenose dolphin, Jeroen Reneerkens
In order to find food, dolphins use their ears instead of their eyes. The animal can emit high tones from its head which echo off a fish. This echo is received in its lower jaw. This is called echolocation and dolphins are able to determine how large the fish is, which direction it is swimming and how fast. The dolphin can even regulate the strength of the signal. In a noisy sea, the signals must be louder than in a calm sea. Dolphins and porpoises live in a world of sound, which makes them particularly sensitive to noise made by humans underwater, such as ship motors.
Dolphins can recognize each other by their own unique whistle. Similar species recognize the noise and use it to call each other. - Threats
- Porpoise on the beach, ecomare, salko de wolf
The number of dolphins and porpoises declined sharply between 1940 and 1965. In those days, fish contained high levels of toxic materials. Because these marine mammals eat fish, they were very much affected by this material. In addition, the fish populations also declined rapidly, so that there was less food to eat. To make things even worse, the amount of noise under water at sea strongly increased due to increasing shipping and construction at sea. Dolphins orient themselves with the help of sound and are greatly bothered by extra noise. Fish nets are also dangerous for dolphins. If they get caught in them, then they can't get to the surface to breathe and therefore suffocate. In order to prevent catching dolphins and porpoises in fishing nets nowadays, pingers are placed by the nets. These make pinging sounds under water to warn the animals of danger.
- Protection
- Common dolphins, Marijke de Boer
In 1991, a number of countries signed the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS agreement). The countries oblige themselves to protect the habitats of the small cetaceans, to collect data for scientific studies, to decrease pollution and to spread information.
If porpoises and dolphins wash ashore, they are difficult to save. Nevertheless, the organization SOS Dolphins located at the Dolphinarium in Hardewijk tries to save as many as possible. Various centers along the coast, including Ecomare on Texel, have special equipment for first aid, after which the animals are transported to Hardewijk. If they succeed in saving the animal, it is returned to the sea.
- Sleeping and breathing
- Dolphins, marijke de boer
Dolphins do not breath unconsciously like people. They must continually think about their oxygen needs, otherwise they will die. Sleeping in a human sense would lead to their death, therefore they have found a different method. They can let one half of their brain sleep while the other half takes over a number of functions. This way, they can sleep safely.
If a dolphin is wounded, other dolphins often help out. They hold the wounded animal above water until reaching a safe place. That dolphins would do the same with humans is probably a fable.
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