Eyes and ears and DNA tests below the water line

Until recently, researchers had two options to map out underwater biodiversity. They would dive under water themselves to see which species of fish lived in a certain place. They would also fill vials of water from a boat, at a lock or dam, and take it to the lab to analyse the DNA. This is especially useful in places where diving is difficult. This also enabled them to determine which species had visited that location in recent hours or days. But how do you combine the trained look of the diver with the taking of DNA samples? With that in mind, marine animal ecologist Reindert Nijland and his colleagues started building the Fish Sensing Box at the end of 2021.

This device, almost the size of a diver, performs multiple functions simultaneously to observe the marine life. “The Fish Sensing Box has a camera, a hydrophone to record sounds, and 24 jars that can take a water sample independently, for example once a day,” explains Nijland. The device pumps the water over a filter and conserves the samples. In the lab, the researchers determine to which fish the DNA in the sample belongs – or to which marine mammals, lobsters or worms. This shows which species were nearby during or just before sampling.

Lock or estuary

The first sea and river pilots have now been completed. Nijland now wants to implement the box at other locations. “You can reach places at sea where you can't dive because of bad weather or depth. Diving is also unsafe in locks or river estuaries, where there is a strong current. These locations are suitable for the device. It will be especially interesting to map the migration of fish in those locations.” This is because some species of saltwater fish use the rivers to reach places where they can reproduce.

Nijland is also thinking of research into the construction of wind farms. The question there is to determine for which species these are unfavourable or perhaps beneficial circumstances. “We want to visit locations where these farms are planned. We will first measure several weeks before construction starts, and then during the construction and several years after the construction, for example. Often, legislation and regulations prevent easy access to wind farms. You need special ships to get there. If you can leave something down there that does the observations for you, that is ideal."

More DNA analyses

They're not there yet. First, the researchers want to know whether they can use the retrieved DNA to also determine how many fish have passed, and how long ago that happened. By linking DNA, image and sound via software, Nijland wants to get an even better picture of the composition of species. “And we hope that in future the DNA analyses will also help us to distinguish between individual fish or marine mammals and perhaps even to determine how old an animal is.”

The ideal device will also perform the DNA analyses itself, and will be a hand-held size that can be connected to an underwater drone. This will provide even more opportunities for researching the underwater biodiversity. Nijland: “I think it's so cool that you could be sitting at your computer and receiving data from a device that is out at sea. That the device can hear a dolphin or certain fish species passing by, and then take a water sample right away. That is what we are working towards.”