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Since 2019, scientists have tagged cod in western Norway only to “disturb” them with noise during the spawning season. The objective is to be able to give better advice on seismic studies.
The Institute of Marine Research (IMR) advises on all seismic surveys carried out in Norwegian waters. One tip is to avoid seismic shots during the spawning period, which is critical for fish survival and reproduction.
The background for this review is a large-scale experiment that was conducted in the 1990s. In this study, it was found that cod and haddock were scared away from the area during seismic shot.
However, the study was conducted on fish grazing in the Barents Sea during the summer.
Cod tagged in the spawning area
“No similar studies have been done on cod spawning, and it was uncertain whether the same avoidance behavior would be seen during spawning season. That’s why we started the SpawnSeis project. says marine researcher Lise Doksæter Sivle.
Starting in 2019, researchers tagged cod with acoustic transmitters in the Bakkasund spawning area in the municipality of Austevoll in western Norway as part of the SpawnSeis project.
In two seasons (2020 and 2021), researchers went out with air cannons and exposed the cod to seismic fire during the spawning period. The results of these experiments are expected to be published this year.
Test new technology
In the spring of 2022, researchers conducted new experiments with a new seismic investigation technology called a marine vibrator. Instead of firing shots intermittently, like air guns, the vibrator emits a lower but continuous sound.
“One hypothesis is that marine vibrators may scare fish and marine mammals less than compressed air guns, since the sound is lower, and they reduce the risk of hearing damage,” explains Lise Sivle. “On the other hand, it could be that the constant noise of the vibrator causes the cod to move to a quieter area, or that it reduces the vocalization that is absolutely essential for successful spawning.”
Buoys receive signals from cod
In Bakkasund Bay, where the experiment is taking place, the researchers deployed a network of listening buoys, or receivers, which receive signals from tagged cod. This is a type of technology also called telemetry, which means distance measurement.
“Receivers record information about the location, depth and acceleration of cod. When a cod is registered by three different receivers, the position can be accurately estimated in three dimensions,” explains postdoctoral researcher Kate McQueen.
Telemetry and big data analysis are increasingly used in marine research. It offers completely new opportunities to understand how animals move in nature and how they react to different environmental conditions.
Provides a basis for good advice
In May and June, marine scientists – aided by local fishermen – went out to retrieve data and change batteries from overgrown receivers in Bakkasund. After downloading the data and changing the batteries, the receivers are ready to return to sea and collect cod data for another year.
In the meantime, data from the last spawning season must be prepared for analysis and publication. When the data from this year’s experiment is compared to the results of previous SpawnSeis experiments, it will be possible to answer how the marine vibrator affects fish compared to traditional air guns. With this information, marine researchers will be able to provide up-to-date, knowledge-based advice on future seismic surveys.
About research projects
- In the SpawnSeis project, we investigated how the sound of seismic airguns affects the spawning behavior of cod.
- SpawnSeis started in 2018 under the leadership of IMR with support from the Research Council of Norway and Equinor.
- Other research partners were the Norwegian Defense Research Institute (FFI), TNO and Leiden University as well as the University of Lisbon.
- In 2021, SpawnSeis was expanded to also study how the sound of a marine vibrator affects cod spawning.
- This sequel, SpawnSeis MVis carried out by the Norwegian Institute of Marine Research and the Norwegian Institute of Defense Research with support from Equinor, Shearwater Geo, Vår Energi and ABP Norway (formerly Lundin Energy Norway).