In situ TS measurement of capelin (Mallotus villosus villosus) in the Barents Seaat 38 kHz

No abstracts are to be cited without prior reference to the author.

Now the acoustic target strength relationship TS = 19.1 log(TL) – 74.0 is used in trawl-acoustic surveys (TAS) on assessment of capelin (Mallotus villosus villosus) stock. In this report we present results of in situ TS measurement of capelin for different length TL at the frequency of 38 kHz obtained by PINRO in the Barents Sea in 2000 -2004 during trawl-acoustic survey (TAS) of capelin stocks. The research vessels we have used, R.V. 'Persey–3', 'AtlantNIRO', 'Smolensk' and 'Fridtjof Nansen' are equipped with SIMRAD EK500 and EK60 scientific echo sounders with the split-beam transducer for directly measuring fish target strength. The echo sounders are connected to an IBM PC with the specially developed software packages LTSD100 (Length and Target Strength Distributions) and FAMAS (Fisheries Acoustic Monitoring & Analysis System) to collect and process results of measuring fish target strength. Simultaneous check hauls of the studied fish concentrations were conducted by pelagic and bottom trawls with small-meshed size insertions for estimation the length composition and the mean length (TL ) of capelin. Based on the analysis of all the data we defined the acoustic target strength relationship for capelin of length 4.4-18.7 cm: TS(PINRO) = 21.4 log(TL) –75.4. On our opinion, the currently used relationship TS = 19.1 log(TL) – 74.0 probably giving understated target strength values and the biomass are overestimated to 10 – 30%. In PINRO in the sea expeditions the works on determination of capelin target strength in situ of different length in different seasons in the day and night time and for different depths still continue.