The past summer, I successfully completed a motorboat course to enable me to drive a motorboat on the Bodensee, required for my ongoing research on fish collective behaviour. I got my “Sportbootführershein” in the post a couple weeks ago, and finally this weekend was able to ‘take the boat out’.
In the cold rainy weather of early November, I set-off with with a good friend on one of the motorboots from the Limnological Institute. The water was considerably clearer than during the summer, providing a visibility of just over 5 meters. It was beautiful being out on the water. However, in the first hour almost being out, we still hadn’t seen our first fish!
We navigated around the island of Mainau, and started exploring the very shallow areas near the mainland. I was a bit annoyed I hadn’t seen any fish yet, let alone any sticklebacks, but when we decided to cross under the bridge leading to Mainau we suddenly found thousands of them!
The water was so shallow that it was necessary to take the motor out, and continue by oars. But this also meant we could observe the swarming fish from very close. Despite sticklebacks being very abundant in the Bodensee, in the autumn and early winter most of them move to deeper waters, likely following the movements of their invertebrate prey. These remaining fish were apparently some of the last ones remaining in the shallows, likely seeking shelter in the shadow of bridge, and I was therefore very happy to have found them.
We spent about half an hour observing their movements and behaviour and I got some good ideas to come back for some more quantitative field measures of their group sizes and compositions. After that we decided to go for a quick snorkel before going back to the harbour.
With my freediving wetsuit, the 11 degrees C actually still felt very comfortable, and I was enjoying the relatively clear waters of the lake. The Bodensee has a very interesting geology, with relatively shallow water on its edges that can suddenly drop almost vertically tens and tens of meters into the deep.
We only snorkeled a bit above a drop-off near the harbour to check our wetsuits and the visisbility, which both passed our expectations. I therefore can’t wait to go back again and take the boat out the lake to catch wild individuals for my experiments, get some more quantitative observations of the sticklebacks and their predators, and explore underwater.