Finding fish schools by echo
After graduating as a freshwater and marine biologist from the University of Amsterdam, Margot Maathuis worked for an ecological consultancy. ‘But the attraction of scientific research remained,’ says Margot. ‘The societal importance of fish appealed to me. Fishermen earn a living from fish, people eat them. In addition, fish are mobile, respond strongly to their environment, and form an important part of the food web. That’s very interesting from a biological point of view.’ She did volunteer work for years, in the sampling programmes on the NIOZ tidal flats, took part in an Atlantic voyage on the NIOZ research vessel Pelagia, and has been a recreational diver since she was twelve.
Echosounder
Margot will use acoustic techniques to track small pelagic fish such as herring, sprat and anchovy – in the tidal inlets between the islands. One of these techniques is carried out on board a ship equipped with an advanced ‘echosounder’, a device that transmits sound pulses, which are reflected by fish. From the echoes received, the size and density of a school of fish can be determined, as well as its location.
Exciting
The data obtained from the echo sounding can be used to build up a picture of the depth at which fish swim in the area, and how many of them there are. It will be a little tense using the ultrasound equipment, Margot says: ‘The Wadden Sea is relatively shallow, and this method is usually used in deeper water.’ It is too early to say which fish species are involved. In order to get an idea of what the ultrasound equipment ‘sees’, fishing will also be done regularly, and Margot will sort the catch according to species and age. Clearly, she will still often be found on board a research vessel.
