Simrad makes fish species identification possible

Simrad, the professional fishing and fishery research division of Kongsberg Maritime, has developed alongside the Institute of Marine Research, Norway, an echosounder system capable of discriminating between different fish species.

Simrad, the professional fishing and fishery research division of Kongsberg Maritime, has developed alongside the Institute of Marine Research, Norway, an echosounder system capable of discriminating between different fish species.

Recent research has shown that simultaneous use of several discrete

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echosounder frequencies (multifrequency) not only improves fish stock estimates but can also be used to identify species, because each specie has a unique acoustic frequency response. This new and growing understanding greatly improves the value of hydroacoustics to obtain information about marine resources.

Scientists at the Institute of Marine Research, Norway, have shown that different species of zooplankton and fish can be identified based on multifrequency acoustics. One example is given in the echograms in figure 1 where schools of mackerel are observed simultaneously at the frequencies 18, 38, 70, 120, 200 kHz using the Simrad EK60 echosounder.

The schools of mackerel can be seen in the left part of the echogram. It is clear that the echo from the schools becomes stronger with increase in frequency. This response is unique to mackerel and can be used to discriminate mackerel from other fish species.

The echograms in figure 2 are a recording of a layer of krill at the same frequencies as above. As opposed to the mackerel, the strongest echo from krill is obtained at 70 kHz. The frequency responses of mackerel and krill are clearly different and can be used to identify and discriminate these species.

In the future, databases of 'acoustic signatures' for the different commercially interesting fish species will be established and Simrad is already developing echosounders that can take this information into practical use.

“Single frequency echosounders have traditionally been used to locate fish resources and to determine their size, both at population and individual level. With the high exploitation rate on limited fish resources seen internationally, selective fishing has become a major topic in fisheries management. Simrad's development for fishery research systems can help the industry as a whole,” comments Frank Reier Knudsen, Fishery Biologist, Simrad.

For further information, please visit the Kongsberg Maritime Stand 650 at Oi06.

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