By installing a stereo video camera in the trawl, researchers at the Swedish University of Agricultural Sciences want to reduce the need for trawling in acoustic fish surveys. The technology is now being tested on board SLU's research vessel R/V Svea, under the scientific Baltic Sea expedition Spras.
"We want to catch fish, but not more fish than necessary," says Hans Nilsson, who is leading the experiments and works as a researcher at the Department of Aquatic Resources at SLU (SLU Aqua).
The purpose of the Spras survey is primarily to collect data on sprat, but also on herring and stickleback. The three small pelagic species that live in the open water column, and are monitored with a combination of acoustic methods (sonar) and trawling.
During the first three days of the expedition, the investigations have been supplemented with a Camsounder, a system developed by Norwegian Scantrol Deep Vision. The system consists of an underwater unit with a stereo camera, lights, battery and acoustics attached to the trawl.
“During a haul, all the fish that swim into the trawl are photographed. With the help of a software, we will be able to register species and lengths automatically. In addition, images with depth and time information are logged," says Eirik Svoren Osborg, engineer at Scantrol Deep Vision.
The system thus identifies and measures the fish below the surface in real time. If you only need basic information about species and size, you could fish with an open trawl bag and release the fish alive.
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“On some surveys such as Spras, we will always need to take fish on board to do biological analyses (such as age, individual weight, diseases and parasites). With this technology, however, we could get a good idea of how many and how big fish we have already caught, and finish the haul when we don't need to catch any more individuals," says Hans Nilsson.
In Sweden, unlike in the rest of Europe, fish caught during the test fishery are counted as laboratory animals. All Swedish authorities that use laboratory animals strive for what is known as the 3Rs. The three R's stand for: replace, reduce, and refine.
"With a system like this, it is possible to reduce the amount of fish that are caught and killed. And it can also help to refine our sampling. With the camera, we can collect more information, such as the depth at which the species swim and how they behave. It increases our knowledge of the entire ecosystem," says Hans Nilsson.
"With a system like this, it is possible to reduce the amount of fish that are caught and killed. And it can also help to refine our sampling. With the camera, we can collect more information, such as the depth at which the species swim and how they behave. It increases our knowledge of the entire ecosystem," says Hans Nilsson.
The experiments on board R/V Svea – which will now be evaluated – are part of a three-year project at SLU, where other non-lethal technologies such as eDNA and advanced hydroacoustics are also being evaluated. The projects are financed by the Swedish Agency for Marine and Water Management through funds from the EU Fisheries Fund.
The tested camera is a newly developed product adapted for commercial commercial fishing, where it is hoped that the technology there will contribute to more profitable, efficient and environmentally friendly fishing.
"The system is being developed continuously, and I hope that we can acquire our own trawl camera and carry out a more comprehensive scientific evaluation. Our first attempts are promising," says Hans Nilsson.
The ongoing project on 3R is a continuation of previous work at SLU Aqua that has analyzed and evaluated different techniques for non-lethal and non-invasive sampling methods. Read the report ”Provtagningsmetoder av akvatiska resurser med 3R i fokus” (in Swedish)
SRAS -Sprat Acoustic Survey
The expedition's target species is sprat. The main purpose is to collect information about stocks in the Baltic Sea. The survey is one of the six internationally coordinated trawl surveys that SLU conducts in the Baltic Sea, Bothnian Sea, Kattegatt and Skagerrak every year within the framework of the DCF (Data Collection Framework).
Hans C. Nilsson, Researcher
Department of Aquatic Resources, Institute of Marine Research, SLU hans.nilsson@slu.se , +46 10 478 40 40