Seismic surveys are loud. They send intense sound pulses into the sea to search for oil and gas. But such sounds can disturb fish, especially when they are spawning. This is one of the reasons why scientists turned Bakkasund and Kalsvika into a living laboratory.
If you sail through these fjords on Norway’s west coast, you may notice orange buoys in the water. They are marked with the name of the Institute of Marine Research. Some fishermen have even caught cod with small tags in the fin or battery-like objects inside the body.
Tracking Cod with Telemetry
The method is called telemetry. Under the buoys sit small acoustic receivers. These receivers pick up signals from transmitters placed inside the fish.
Each transmitter has a unique sound code and also measures depth. In this way, scientists can follow the movements of each cod for up to two years.
The project started in 2017, with one precise aim: to find out how spawning cod respond to seismic sound. The fjords were perfect for this type of work. They are sheltered from bad weather, and the cod here are stationary. Since 2018, around 50 cod have been tagged every year.
How Fish React to Noise
The results show that cod do not swim away from their spawning grounds. But they do change their behaviour. When exposed to seismic sound, they dive deeper and move less.
The same happens when they hear a new sound source called a marine vibrator. This device makes a softer but continuous sound. Strangely, the constant sound may disturb fish more than the louder pulses of a seismic gun.
These findings raise new questions. What about ship traffic? What about the steady hum of offshore wind turbines? Do cod respond differently outside the spawning season? To explore this, scientists have tested larger air guns, research ships, and underwater speakers that mimic turbine noise.
New Insights into Spawning
The project has also revealed new knowledge about spawning. Male and female cod use different depths. Males stay close to the seabed, while females swim down only when ready to release eggs.
This research helps Norway make better rules for seismic work near spawning areas. It also gives advice for planning offshore wind farms, a fast-growing industry.