In the last few weeks acoustics research has shifted into focus more and more. Some exciting things have happened, some stories worth telling.
At the beginning of this year’s field season, we had deployed a few hydrophones (underwater microphones) to listen to the underwater world of northern Iceland. Since we have dropped them into the water, they have been collecting data every day all by themselves. Now, several weeks later, we are dedicating time to acoustics again, to watch, retrieve, listen, and deploy…
Skjálfandi deployment: Scan sampling
One hydrophone had been deployed in Skjálfandi Bay, our well-known research site, in the end of June this year. We want to investigate the impact of vessel noise on the humpback whale’s communication behavior. Since we had a hydrophone in the water last year as well, it will be interesting to compare the recordings from 2020 the Covid-season (where so little whale watching happened) with this summer in 2021 (where the number of tourists and therefore boat trips has increased drastically again). The recordings by themselves can answer many important questions, only by listening. How loud is it in Skjálfandi Bay? Are vessels a major cause of the noise compared to natural forces like wind or waves? Are the whales calling differently when vessels are around? For the last question it is especially helpful not only to listen to the underwater acoustic world but also to get a visual reference. Ideally an observer on shore, who confirms what you can hear. For this reason, two of us went on a camping trip to the western side of the bay.
Captain Alli picked us up in the evening. We loaded the boat, left the comfortable town of Húsavík, and drove across the bay. We were excited to approach the remote and wild mountain range ahead, no roads, no people – only sheep, cliffs, and blueberries. Landing on the beach was a challenge. Luckily, we had already done this last year, so we were prepared. We jumped from our motor yacht onto a tiny inflatable and rowed to the beach. With only a little bit of splashing we managed to get everything safely ashore. One last wave to the colleagues on the boat and we were alone for the next 6 days. We climbed up the cliff, bringing all our equipment to the beautiful tip where you can see all around the bay. It was wonderful to be back! We pitched up our camp, the theodolite (which measures the position of objects) and slept, in order to be prepared for the long days ahead. The next morning, we started our surveys. Both of us stood at the cliff edge, scanning the bay for any cetacean we could find. Our goal was to find every cetacean (or group of cetaceans for dolphins) within half an hour and mark their position with the theodolite. Knowing how many animals and where they are in the bay at a given time will later help to better interpret our acoustic data. For example, if we hear 10 calls within 30 minutes, it is interesting to know if there was only one humpback whale present likely making all of these calls, or if there were five whales, on average only calling twice each. So, we spent lots of time looking for whales. This is called scan sampling. For half an hour we counted the whales, then we took one hour off. Then the next survey began. From morning to evening we followed this schedule. Luckily, the weather was steady most of the time, not too much wind, no rain and sometimes even the sun greeted us on our cliff. And not only the weather, also the whales were cooperative. Nearly every survey we found humpback whales, sometimes up to 6 individuals. They spent most of their time in the central and north-western parts of the bay, not super close to us, but within our visual range. Once in a while some minke whales showed up predominantly in the south and we spotted a few porpoises. The main stars of the surveys, however, were the white-beaked dolphins. Most days they were everywhere! So many! Wherever we looked, we spotted their large dorsal fins or their jumps. It looked like they were having a great time. What a pleasure to watch. In between surveys, we enjoyed spending our time juggling, eating, playing the guitar or simply chatting. It was difficult, however, to take our eyes off the water, to relax them for the next survey. When the time had come that we were getting low on food and toilet paper and the weather was supposed to turn windy we were sad to leave our peaceful cliffs.
A few days later we came back for another 1.5 days of surveying, this time even accompanied by a film crew. The visual impressions of our cliff top adventure will therefore follow later in the form of a short movie created by Thomas Bour.
Skjálfandi deployment: Retrieval
Now that we had visual observations accompanying our recordings, we were ready to retrieve our hydrophone. To see if we could hear the whales we had been watching. So, on the 15th of August we embarked our research vessel Arcpath with captain Alli, hoping to return with the hydrophone on board. Organizing the retrieval had been a challenge of its own. When you want to deploy a hydrophone at 50 m depth you need a way to get it back up. Therefore, you attach an acoustic release between the anchor and the hydrophone. As soon as you want to retrieve your equipment you send out an acoustic signal from a boat, the release opens, and everything floats back to the surface. To send this signal you need a deck unit with a transducer but getting this deck unit turned out to be more complicated than expected. We had organized a rental from the UK months ago. Now, a few days before they were supposed to send it to Iceland, they couldn’t find their own equipment anymore. They just couldn’t find it! So, we had to organize another deck unit. Luckily, we found one and it just arrived in time. Last Sunday we were ready to retrieve our hydrophone, going back to the GPS location where we had deployed it. We dropped the transducer in the water and asked for a range to the release. Seeing the answer made us very happy! An answer itself is great news, it means the acoustic release is still around and alive. And it said 47 meters, that meant it’s right below us. We pressed the buttons to release and sure enough a few seconds later Captain Alli spotted the buoys on the surface. We picked it up and had the hydrophone back safely in our hands. What a relief! We drove back, cleaned the equipment, and plugged the instrument into the computer. It had indeed recorded! We downloaded the many gigabytes of data and started listening. Soon we heard the first humpback “whups” and some dolphin whistles. Familiar sounds from our last year’s recording. Then we checked a day where we had seen pilot whales in the bay. The recordings didn’t disappoint us, the pilot whales were whistling and clicking so beautifully! What a success! Now we have a lot of data that is waiting to be analyzed. It will be so exciting to compare these data with the recordings from last year, now, that tourism has increased again!
But this is not yet all the progress in the world of acoustics. After we got our hydrophone back safely, we charged and programmed it again for another journey. We took it to the east of Iceland and joined the sailing yacht Northabout of the Unu Mondo expedition (www.unumondo.org). Together we sailed into the Finnafjörður and deployed the hydrophone again. It will stay here for a full year and will provide baseline data for an area without much human impact. There is no commercial whale watching in this fjord, only a few fishing boats. But in a few years, a large harbor is supposed to be built here and we are excited to get acoustic data before this big intervention. We hope to document the change in soundscape and maybe even in animal calling behavior. Fingers crossed the hydrophone will be retrieved again successfully next summer!
Drone noise testing
Finally, two more acoustic projects will be the focus of our research in the next two weeks.
We are currently starting a project where we want to find out, how loud drones are under water. We had initially tested this out of curiosity in July with a tiny hydrophone (not calibrated). We had expected that there wouldn’t be much noise, since this was what one other study had found. However, when we looked at the data, we were surprised to hear the drone very clearly! Even at 30m height! So, we decided to start a proper experiment with a calibrated hydrophone to quantify the impact. We have now finished the planning and went out on the water for the first time yesterday. We are testing three different drones – our Phantom 4, a Mavic Pro and an Inspire 1 (the latter two from Maria, a PhD student here in Húsavík studying body condition of the cetaceans of the bay). We are flying the drones at different heights and different distances from the hydrophone to see which of these two variables has a higher impact on the noise. Additionally, we will repeat these tests at different hydrophone depths. Our first day of testing seemed fairly successful. Even though the process took longer than expected and we had to stop early because of incoming boats, the flights we managed to do worked well. When we came back, however, we had a horrible surprise: the hydrophone had been leaking and was damaged beyond repair! Initially we thought this would put an end to our experiments. Luckily, it turned out though that Marianne, director of the local research center, had a spare Soundtrap we could use. So, we can continue our testing in the next days. We are very excited to see what we can find. Hopefully, we will be able to use the results to drone over the whales with as little impacts as possible by flying appropriately and maybe even inform other scientists who use drones to do so as well.
The last project regarding acoustics this summer is a rather experimental one. At the beginning of the season, we had deployed three tiny hydrophones called Hydromoths in different fjords/bays in northern Iceland to compare their soundscape or to identify the occurrence of whale calls over the summer. We might even try to correlate the amount of cortisol in the breath of humpbacks whales (if we take enough blow samples) with the noise that these animals might be experiencing. One of these Hydromoths was attached to our Soundtrap in Skjálfandi bay. It was retrieved successfully when we picked up the equipment with the acoustic release. The other two Hydromoths will require a more adventurous retrieval. They are not deployed with releases, so we will pick them up diving. At the end of August, we are planning to dive in Eyjafjörður and Steingrimsfjörður and hope to find the instruments again. This will be another exciting story!