The role, behaviour and biology of animals
Seeing, hearing and testing underwater
Soon, the Fish Sensing Box will be the eyes, ears and laboratory for researchers who want to know about the species that live under the water’s surface. This will give a better picture of biodiversity in places where diving is difficult or impossible. Researcher Reindert Nijland explains why the Fish Sensing Box is such an important asset to their underwater biodiversity research.
Locks and weirs may make rivers more navigable but they also have disadvantages. Hydraulic engineering structures such as these form a major obstacle for fish. Their presence – and the fish ladders and other ‘bypasses’ that are then built to allow the fish to swim further – affect the diversity of wildlife in the water. At sea, wind farms, electric cables and drilling platforms also cause changes in underwater life. The construction work can be a temporary disruption; once the structure is in place, some animals and plants will stay away while others may be attracted to the new habitat.
Until recently, two approaches were used to study underwater biodiversity. Firstly, researchers dived to see what fish species lived in a certain area with their own eyes. Secondly, researchers stood on a boat, lock or weir and filled test tubes with water that they took back to the lab for analysis of the DNA. This was particularly useful in places where it is difficult to dive. This approach also told them which species had been in the area in the past few hours or days. But to get the best results, you would want to combine the experienced eye of the diver with DNA samples. With that idea in mind, marine animal ecologist Reindert Nijland and his colleagues started building a multi-functional device at the end of 2021.
‘The Fish Sensing Box has a camera, can record sounds and can take water samples independently’
Their invention is called the Fish Sensing Box. It is almost as big as a diver and it has several different functions in observing life underwater. “The Fish Sensing Box has a camera, a hydrophone to record sounds and twenty-four jars that it can fill independently with water samples, for example one a day,” explains Nijland. The device pumps water across a filter and preserves the samples. In the lab, the researchers analyse the DNA in the sample to determine what fish – or marine mammals, crabs or worms – it comes from. This shows what species were in the vicinity when, or shortly before, the sample was taken.
The first tests in rivers and the sea have now been completed. Nijland is still busy analysing the data. Then he wants to suspend the box in water in other places. “You can use it in parts of the sea that you can’t reach as a diver, for example because of the bad weather or the depth. It is also not safe to dive near a lock or in the mouth of a river because of the strong currents, but you can use this device. Those are precisely the kinds of places where fish migration gets interesting.” After all, some saltwater fish use the rivers to get to places where they can reproduce. The offspring then swim back to sea.
Nijland also has locations in mind at sea where he would like to use the Fish Sensing Box. For example, he wants to study the effect of the construction of wind farms. The question is which species are adversely affected and which species may in fact benefit. “We want to visit locations where wind farm construction is planned and carry out measurements a few weeks before building work starts, followed by measurements during construction and again a couple of years after the wind farm has been completed, for instance. Wind farms are often not easy to get access to because of the regulations. You need special ships to get there. If you could deposit something that can do the measurements for you, that would be ideal.”
However, the research with the Fish Sensing Box has not yet reached that point. First, the researchers want to know whether they can use the DNA findings to determine how many fish swam nearby and how long ago that was. DNA disseminates quickly and will also have completely broken down within a few hours to a few days. “If you find some DNA, it isn’t clear whether a lot of fish swam past a couple of days ago, or one fish very recently. If a seal ate a single fish right next to the box, that may leave you with a lot of DNA, giving the impression of large numbers of fish.”
Nijland wants to develop software to combine DNA, images and sound and thereby get a better picture of the mix of species. “We hope the DNA analyses will eventually let us distinguish individual fish or marine mammals and perhaps even determine how old the animal is.” If the animal happens to be fitted with a transmitter, the device should soon also be able to receive any signal it sends.
Ideally, the instrument will even perform the DNA analyses itself and be a convenient size that fits inside an underwater drone.
In other words, Nijland plans to have the box house a mini-lab and then gradually shrink the whole setup. To do this, he is collaborating with Delft University of Technology and the spin-off company Lobster Robotics. A Fish Sensing Box that could move of its own accord would offer even more opportunities for research on underwater biodiversity. Nijland: “I think it would be really cool if in future you could sit at your computer and have data coming in from a device on the seabed. Imagine the box hears a dolphin approaching or a particular species of fish and immediately takes a water sample. That is what we are working to achieve.”
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MORE INFORMATION This project is part of the Next Level Animal Sciences (NLAS) innovation programme.
Participating researchers of Wageningen University & Research collaborate with various partners to develop new research methods and technologies within the field of animal sciences. NLAS consists of three research directions, namely sensor technology, complex cell systems and data and models.