Luke conducts sonar survey of fish populations in Lake Inari, Finland

The Natural Resources Institute Finland (Luke) is assessing the fish populations in Lake Inari using sonar technology. The sonar survey focuses particularly on the presence and abundance of the whitefish population, as well as the important char and vendace stocks.

Using sonar, the team can identify fish by the shape of their echoes reflected back to the device. Project manager and researcher Nico Alaoravainen explains, “When the sound hits a fish, its shape corresponds to the echo we receive. This allows us to infer the type of fish based on the size of the echo displayed on the sonar screen.”

A submersible drone accompanies the survey vessel, allowing for comprehensive imaging and identification of fish. The drone is equipped with depth and temperature sensors that provide valuable information about the fish’s habitats. “In Lake Inari, fish schools can swim at depths of up to ten meters. We are currently investigating whether the light under the surface is sufficient for the fish to be visible in the drone’s images. While the drone has additional lighting, too much brightness might repel the fish,” Alaoravainen added.

Currently, the sonar team is testing and calibrating the equipment in Lake Inari, with the main research activities set to begin next week. The sonar data will be validated through trial trawling to collect fish samples.

Lake Inari, Finland’s second-largest, spans 1,083 square kilometers. It formed during the Ice Age, with an open connection to the Arctic Ocean existing for a period after the ice retreated about 9,000 years ago. There are various areas with distinct fish species within the lake. Depending on weather conditions, the team aims to survey four areas in August, as successful measurements require calm weather.

Luke conducts these sonar experiments in collaboration with the Lapland ELY Centre’s fisheries authorities, funded by the Ministry of Agriculture and Forestry, with results expected this winter to enhance understanding and management of Lake Inari’s fish populations.