AMIGOS cruise: Monitoring Marine Mammals from the Strait of Gibraltar to the west coast of Ireland

Dr Ellen White

University of Southampton

In October 2024 I was offered the opportunity to join the AMIGOS survey, ‘Acoustic Monitoring from Ireland to Gibraltar Oceanic Waters Survey’, a research cruise sailing from Lisbon to Galway on the R.V Celtic Explorer. The survey was led by Dr María Pérez Tadeo from the Atlantic Technological University (ATU) and focused on collecting acoustic monitoring data for both marine mammals and underwater noise as part of the EU-funded Horizon project STRAITS (Strategic Infrastructure for Improved Animal Tracking in European Seas). I was lucky enough to be invited onboard to join the marine mammal team, assisting with on deck visual surveys and monitoring the real-time passive acoustic data stream from the towed hydrophone. 

As a researcher I have extensive computational skills to handle passive acoustic datasets but lack field experience as I completing my PhD during the pandemic. The AMIGOS survey presented an opportunity to close some gaps in my skillset related to survey design and science at sea. The Challenger Stepping Stones Bursary provided the financial aid necessary to make this trip a reality, allowing me to experience life at sea and be a part of gathering data that will inform management at a national and European level with respect to underwater noise.

After a delayed start to our trip, and a few bonus days eating far too many Pastel de Natas and exploring Lisbon, we finally set sail on October 20th. Onboard our main scientific goal was to monitor the presence of marine mammals both visually and aurally and record the ambient noise of regional seas as we passed through. To visually observe marine mammals, we stood on the ‘crow’s nest’, the highest point of the vessel, and scanned the horizon and near-field for indications of animal presence. In tandem we also reported the presence of marine pollution and shipping traffic. Observation was easily the best job on the whole ship, particularly early in the morning watching the sunrise over the open ocean.


Along the way we were treated to many sightings including fin whales (Balaenoptera physalus), minke whales (Balaenoptera acutorostrata), pilot whales (Globicephala melas), spotted dolphins (Stenella frontalis), bottlenose dolphins (Tursiop truncatus), and a continuous stream of common dolphins (Delphinus delphis). As we travelled through the Gulf of Cadiz, the Strait of Gibraltar and into the Mediterranean we knew there was a high chance of spotting sperm whales (Physeter macrocephalus), blue whales (Balaenoptera musculus) and even killer whales (Orcinus orca), but unfortunately it was not to be. It was a strangely quiet passage for marine mammals, potentially a sign of changing oceans? Mammal sightings occurred at all hours of the day, and into the night, ranging from animals swimming meters from the boat to very faint blows in the distance. Unfortunately, we ran into some bad weather in the Mediterranean which stayed with us until we reached the Bay of Biscay, disrupting our ability to visually observe the water, which may be the reason for the low sighting numbers. During spells of poor weather and high swell we had to conduct observations indoors from the bridge, which led to several members of the team suffering badly with sea sickness and restricted our ability to survey long distances from the ship. Ironically, we had all of our bad weather in the southern part of the survey and by the time we were traversing the west coast of Ireland we had flat seas and minke whales feeding, it was spectacular!


When not on deck conducting visual surveys, I was stationed at the passive acoustic desk monitoring the real-time live feed streaming from the towed hydrophone. By monitoring the spectrogram (a visualization of the frequency components of the received sounds, see photo) and listening with headphones we could identify animal presence acoustically while on transect, the acoustic data was then archived for post-cruise processing. As a passive acoustic researcher, I am fascinated by the cacophony of sounds that occur underwater and I thoroughly enjoyed monitoring the soundscape as we moved north, identifying acoustic sources such as cargo ships and fishing sonar as well as the biophony.


Alongside the marine mammal team, we had a trio onboard dedicated to bird surveying who kept a rigorous log of literally every single bird they saw along each transect. It was amazing to watch them in action, identifying birds often kilometers away that were merely a speck to me. The bird team also assisted with marine mammal observation as often birds are a pre-cursor for a sighting, particularly during a feeding frenzy. It was very interesting to the see the very strong shift in species as we traversed north across lines of latitude.

A member of the Irish Whale and Dolphin Group (IWDG) was onboard trialling their new thermal imaging camera which is being used to help develop an early warning system for detecting whales from vessels, in an effort to mitigate against ship strikes as part of the Atlantic Whale Deal. The camera, nicknamed WALLE, spent many hours on the observation deck alongside the marine mammal observers. During bad bouts of weather, and after sunset, WALLE was our ‘eyes’ on the sea to spy marine mammals we were hearing on the hydrophone.

Along the survey transect we also had thirty CTD stations, used to gather both oceanographic and acoustic data. When on station the CTD frame would be deployed with several hydrophones strapped to it and held at 100m for 30 minutes to an hour to record the underwater soundscape at depth. When analysed together these profiles will provide a transect of ambient noise levels in European waters. The acoustic data recorded in this way is unusual acquiring short-duration snippets of the sonic habitat, however they provide an invaluable insight into the spatial variability of ambient noise levels in the waters of the Mediterranean and the coasts of Spain, Portugal, France and Ireland. 

The CTD team were collecting water samples at depths up to 2000m to monitor chlorophyll and nutrient concentrations for assessing primary productivity. The samples were analysed in the on-board wet lab where possible, keeping the CTD team busy throughout the night. Our most exciting CTD cast came late one evening near the Strait of Gibraltar when a pod of 30+ common dolphins circled the vessel to explore the CTD and stayed with us for the full duration of the deployment. It was a fantastic encounter, with everyone stood out on deck to watch them for hours. The CTD team regularly had dolphins at their late-night casts, as well as tuna and a suspected shark. We think the vessel lights probably encouraged some squid up to the surface and caused a mini feeding frenzy.


As part of the marine mammal team our responsibilities ended at sunset, unusually for a research cruise, which gave us long evenings to watch movies, play board games, catch up on work and look at photographs taken onboard that day. I occasionally braved the gym when the weather allowed it, although attempting the spin bike during high swell proved for an interesting workout, particularly after three different types of potato at dinner each night! I had a lot of data analysis to get through for my own work and the quiet evenings onboard provided the perfect headspace to get stuck in with few distractions.


I am incredibly grateful for being awarded the Challenger Stepping Stones Bursary, without which this trip to sea would not have been possible. The bursary provided an opportunity to get out of the office and gain practical fieldwork skills covering an array of research disciplines. I have not been around a CTD since my undergraduate days, so to freshen up this skillset was a huge asset, as well as boosting my hours as a marine mammal observer. I am primarily a passive acoustic marine ecologist but have focused mainly on the computational side of this research field for many years. Learning from the chief scientist and speaking with the other onboard scientists renewed my clarity of the end goal of my work, to deliver important information to management and stakeholders in a timely fashion. I bring back to my own research a renewed vision and excitement on the importance of what we do, and the need to rapidly address the threat of noise pollution to marine life. The networking and relationships I nurtured onboard will stay with me for the remainder of my career and I know my path will cross with the researchers from ATU in years to come. Collaborations are already being discussed, and I am excited to see where this work will go. Without the help from Challenger this trip would not have been possible, and I will be forever grateful for my time onboard the Celtic Explorer.


Profile:
I am a postdoctoral researcher at the University of Southampton, developing real-time tools for detecting marine mammals from passive acoustic data as part of project MARLIN. I completed my PhD at the University of Southampton in December 2023 as part of the INSPIRE DTP, where I focused on developing machine learning models for identifying components of the Scottish soundscape to understand the influence of anthropogenic noise regionally. My research interests span bioacoustics, underwater noise, machine learning, and marine ecology, with my focus on using passive acoustic data to answer large scale conservation and ecological questions.