This news article is part of Issue 1 of our annual project newsletter, which chronicles our research from 2021. To view more articles describing our research progress from our first year, read the newsletter in full here.
A key area of our research is assessing the impact of underwater radiated noise from vessels on the behaviour, health, energetics, and populations of aquatic life. Below you'll find key updates from our partners working in this area.
UPC - Barcelona Tech
In the first year of SATURN, partners at the Laboratory of Applied Bioacoustics at the Universitat Politècnica de Catalunya (UPC- Barcelona Tech) have focused our efforts on the design and construction of a dedicated test device. This will allow us to quantify the physiological, pathological and behavioural responses to controlled ship Underwater Radiated Noise (URN) exposure on different marine invertebrate species, such as cephalopods, crustaceans, cnidarians and bivalves. Thus far, the main development is related to the accurate separation of the two main components presented in the generated sound field: particle motion and sound pressure. Recent literature reveals that each can have a distinct effect, depending upon the species.
The test device consists in a pair of 1kN-electrodynamic shakers that enclose a rigid tube at both ends, where the animals will be exposed to ship noise recordings at real-field sound pressure/particle motion levels. The control of the relative phase between the pair of shakers, allow us to generate either a sound-pressure- or a particle-motion-dominated exposure field within the tube. In parallel to the acoustic exposure, the oxygen consumption rate and behavioural assessment will be possible thanks to a built-in respirometry system and a see-through tube.
Meanwhile, at University Leiden we have gathered pilot recordings in the Rhine, a large river with strong currents that is home to various vessels and other water traffic events. We also collected a large series of cross-section recordings in smaller rivers and streams (at 5 x 4 locations), at various depths and distances from the river bank (in the Grift-Eem water system). These recordings aim at gaining understanding about recording natural soundscapes in a standardized way and getting insight into quiet and moderately busy waterways in use by migratory fish.
Above Left: Kees te Velde, a SATURN PhD-student at Leiden University wades in a wetsuit to place Soundtrap recording equipment for underwater soundscape sampling of migratory fish. Above right: Pilot recording locations in the Rhine.
Scientists at the Marine Bioacoustics and Marine Mammal Research Labs at Aarhus University are working to better understand how harbour porpoises are affected by the underwater noise produced by nearby vessels. Harbour porpoises are small marine mammals living in cold water, meaning that they require a constant food supply to stay warm. Man-made disturbances, such as underwater vessel noise, can potentially prevent porpoises from finding enough prey and lead to costly avoidance reactions, and hence impact their short- and long-term fitness.
In Danish waters, harbour porpoises occasionally swim into large open pound nets used for catching fish. SATURN Researchers from Aarhus University are called when this happens, and take the opportunity to measure and tag the harbour porpoises, which are then carefully released back into open water.
In Danish waters, harbour porpoises occasionally swim into large open pound nets used for catching fish. This situation has provided our groups with a unique opportunity to work with local fishermen to tag harbour porpoises (under appropriate permits) with state-of-the-art suction cup tags (DTAGs). DTAGs contain a suite of sensors that record and store acoustic and movement information that allow us to quantify their foraging behaviour and energy expenditure as a function of noise load from the environment. After 1-2 days, the tags detach passively due to a loss of suction and drag and are recovered using a combination of Argos satellite systems and radio tracking. Data on the fine-scale diving and foraging behaviour of animals collected by the tags can then be used to assess impacts from vessel noise on the energy balance of the animals. So far, 22 harbour porpoises have been tagged in inner Danish waters, and under SATURN, we have now successfully tagged four more porpoises, providing a total of over 500 hours of high- resolution data.
Institute for Terrestrial & Aquatic Wildlife Research, TiHo
Researchers at the Institute for Terrestrial and Aquatic Wildlife Research at the University of Veterinary Medicine Hannover (TiHo) have also used DTAGs in three harbour seals in the Elbe River. After a preprogrammed period of 22 days, the DTAGs detach from the seals and is then recovered using the Argos satellite system to get an approximate position (within a radius of a few kilometres), followed by UHF tracking, as in porpoises. The large data size necessitates software tools for automatic processing and quality assurance. Our first recovered DTAG has already revealed interesting results, showing that the seal remained within the Elbe river for all 22 days and visited Hamburg Port.
A DTAG (above left) is a type of sensor that attaches to an animal via suction cup and records data for analysis. The tags detach on their own and are recovered via signal (above centre). The track of the animal (above right) is recorded — in this case, the seal remained within the Elbe river for all 22 days in which the tag was attached.
We are now in the process of analysing these DTAG data, both at the University of Aarhus and University of Veterinary Medicine Hannover, to understand 1) how often porpoises and harbor seals are exposed to vessel noise that triggers behavioural changes leading to negative offsets in energy balance, and 2) what the drivers of such responses are in terms of vessel noise levels and characteristics.
To quantify the impact of underwater radiated noise on the health of porpoises and seals, we have analyzed at TiHo the inner ears of stranded (deceased) marine mammals to detect potential cases of permanent hearing loss. We have optimized a new labeling protocol of the inner ear and have collected individuals from several age classes found in the Baltic, North Sea and Elbe river. The majority of the ears are still being processed. We have recently published a case of a neonate harbor seal in the journal Animals, where we found lesions in the inner ear, likely congenital. This information will be important to establish a baseline knowledge on “natural” congenital malformation of the inner ear of harbor seals, to further differentiate from potential damage caused by exposure to factors (including noise) that the individuals might encounter during their lifetime. We also describe the protocol to extract and perfuse the ears in harbor seals that will be implemented in SATURN.
In addition, we will provide updated age- and length specific estimates on general animal health, reproductive capacity and hearing capacity, which will influence animal survival and reproduction. We have reviewed TiHo’s database on the pathological results of stranded individuals, and blood and swap results of all seal catches of the last 30 years, and already selected interesting cases and targeted organs to be categorized in more depth.
Within TiHo, we will also combine clinical health parameters with behavioural recordings in harbour seals to determine how health influences behaviour, and vice-versa. In previous projects we have established immune-relevant and more recently endocrine-related genes in the blood of seals from the North and Baltic Seas, recently published at the journal Aquatic Toxicology, which will be implemented in SATURN. We are currently developing a novel combination of molecular biomarkers in blood to assess noise-related hearing, endocrine and immune responses in harbour seals.
Also at Aarhus University, we are building a simulation tool for assessing impacts of ship noise on harbour porpoise populations. Based on a further development of the existing agent-based population model (DEPONS) we will assess the impacts from underwater noise generated by ships and boats on harbour porpoise populations. Porpoises from different parts of Kattegat have been tagged with long-lasting GPS-tags to get further data for calibrating animal movements in DEPONS. DEPONS is currently parameterized to simulate effects of pile-driving noise only, further development should create a virtual landscape with simulated ships emitting realistic levels of underwater radiated noise based on ship source levels and sound propagation loss. In support of this work, TNO is working on a proper and efficient implementation of ship acoustic modelling in the DEPONS model for assessing population effects of disturbances on marine populations.
For more information about our research into underwater radiated noise and its sources, impacts, and solutions, visit our Research page.