A blog by Saana
Very pleased and relieved to be writing that our acoustic recorder deployment over the last couple of months in Scapa Flow was a success. It is always nerve-wracking to leave scientific instruments on the field, and more so in strong tides and weather, so it is a relief to have both devices back in good condition and full of sound files.
The weather this time of year is more variable than in the summer when we deployed them, and so instead of attempting to cross the Pentland Firth ourselves, we decided to take the passenger ferry to Orkney and charter a work boat from the islands instead. This was definitely a good call in the narrow weather window that we had. We were in great hands aboard MV Viking and couldn’t have asked for more professional and helpful skipper and crew, Hazel Weaver and Helen Hadley, who were really key to the successful recovery on the water.
A fair few flora and fauna had already made a home of the recorder housings – taking advantage of the new habitat space and presumably enjoying the relatively warm and shallow water offering lots of light. Even the hydrophone itself had small growths on them. Such biofouling is common on many man-made ocean instruments and structures, with impacts varying from none at all to significant. In our case, small growths might not influence sound penetration to the hydrophones, but larger growths could influence the flow noise around the recorder. But, the flora and fauna can also be interesting to scientists – something Helen thought about straight away, calling up a friend for the opportunity to pick up a few specimens. It was inspiring to watch the sampling and accidentally being able to help a totally different type of marine life science.
The recording housing before (left) and after (top and middle right). On the right middle panel, note the small red indicator lights at the end of each hydrophone, showing that the recording is ongoing. The right bottom panel shows what the recorder (Loggerhead Instruments LS1) looks like inside, containing the recording board, 4 memory cards and D-cell batteries. To save the memory and increase battery life, the logger was set to sleep for 5 minutes between each 10-min sound file.
The data collection looks promising, with fair bit of orca activity reported in and around Scapa Flow during the recording period (4th August – 5th October). An initial check of the sound recordings already revealed some killer whale calls and clicks coinciding with a sighting by the Sand Eel buoy (link to map) 1 pm on the 27th August. We will be looking for more with the help of citizen science sightings thanks to Sea Watch, Orkney Cetacean Group and Orkney Marine Mammal Initiative. If you have any photos/video of orca in the area during the recording period, please consider getting in touch to share them, as visual observations could really aid in interpreting the recordings in terms of what the whales were doing at the time (such as hunting or socialising). As always, feel free to email Saana and Julia at email@example.com.
The next steps in the sound data processing will include both manual labelling of sounds in a subset of the recordings, as well as applying automated detectors to the whole dataset. The labels will include different noise sources such as flow noise and boats, and marine mammal vocalisations such as harbour seal mating calls, and different types of killer whale calls (pulsed calls, whistles, clicks). Below a couple of samples from our 2019 Flotta Grinds recording:
Acknowledgements As well as the fantastic MV Viking crew, we would like to thank Marine Scotland Science again for the acoustic recorder loan and assistance, Northern Lighthouse Board for their help throughout and allowing us to use their navigation buoys for the study, and Windhaven Cafe, Camping and B&B owners Clare and Phil, once again, for their hospitality. Shout out to also SMRU Instrumentation‘s Steve Balfour for volunteering his time and expertise for both the deployment and recovery trips. Finally, perhaps the single most critical player in the successful deployment was SMRU‘s Simon Moss, who designed, manufactured and tested the new attachment system and weighted housing.