In addition to the seal, another mammal can be found in the Eastern Scheldt: the porpoise. Of a swimming porpoise you usually see no more than the upper part of the back with the dorsal fin, when the animal comes out of the water for a moment to breathe.
Porpoises almost never jump above the water, unlike most dolphins. Because of this, and because they are so small, it is not easy to spot porpoises at sea, especially when there are major waves. An adult porpoise is about 1.5 metres long and weighs 55 kilos. It is greyish on the top and slightly coloured underneath. It lives in small groups of 3 to 5 animals.
Using sound (and especially echoes), porpoises can detect fish traces, obstacles and get into contact with each other. The porpoise mainly eats anchovies and juvenile herring. This is very oily fish and contains a lot of energy. The calmness under water is sometimes disturbed by natural sources of sound, such as storms or heavy rain.
If there is too much noise, porpoises can no longer orient themselves properly. They withdraw into deeper water. Nowadays, it is mainly human noise sources that disturb peace and quiet, for example the engines of boats, although the Eastern Scheldt is relatively quiet.
At the tip of the port head of Zierikzee there is an information column about the porpoise. Here you can hear live if there are any porpoises in the neighbourhood. Underneath a buoy located just off the coast there is recording equipment available. If there is a porpoise nearby, the microphone catches it.
The recordings are sent to the column and a computer makes them suitable for our ears. If you press a button and you hear the clicking sound of the echolocation then there is one close by. With a bit of patience, you can check the water surface until you see it.
If you saw a porpoise, you can put it on the map of the porpoise spotter on the discovery map (ontdekkaart). On this map you can immediately see if there are more porpoises nearby. The more reports, the greater the chance of seeing them.