Influence of hydroacoustic noise from vessel on echo integration estimations of fish stocks and catchability of accounting trawl (on example of walleye pollock in the Okhotsk Sea)

• Main Authors: Michail Yu. Kuznetsov, Vladimir I. Poljanichko, Igor A. Ubarchuk, Eugeny V. Syrovatkin
• Format: Article in Journal/Newspaper
• Language: Russian
• Published: Transactions of the Pacific Research Institute of Fisheries and Oceanography 2017
• Subjects: шум судна; оценка запаса; научный эхолот; реакция избегания; плотность скопления; заглубление; рассеяние; дистанция реагирования; модель поведения; учетный трал; коэффициент уловистости; протраленный объем; vessel noise; fish stock estimation; scientific echo sounder; avoiding reaction; density aggregation; fish deepening; fish dispersion; reaction to noise distance; behaviour model; accounting trawl; catchability coefficient; towed volume of water; Aquaculture. Fisheries. Angling; SH1-691; Okhotsk; okhotsk sea
• Online Access: https://doi.org/10.26428/1606-9919-2017-190-127; https://doaj.org/article/d8c811e1e7d64947855e25a8246d5955

Previously, catchabilty of walleye pollock was estimated for the accounting trawl RT/TM 57/360 by results of acoustic measurements of fish density in the towed layer under fishing vessel. However, fish reaction to noise field ahead of vessel was not accounted in that experiment. Besides, distortion of initial distribution of fish by the vessel noise could cause an error in fish stock estimations by methods of echo integration. Data of new experiment conducted for estimation of fish reaction to the vessel noise are presented using independent floating buoy equipped by scientific echo sounder. Distance of walleye pollock reaction to the vessel noise was estimated as 140-180 m that corresponds to the calculated value (150 m) used in modeling. Distortion of typical fish distribution was considerable: the fish density decreased in the upper layer and gradually increased in deeper layers as the fish moved down. The density decreasing in the layer 0-100 m was evaluated as 0.56, i.e. the echo integration method underestimated the fish density on more than 40 %, the decreasing in the layer 100-200 was less significant (0.86). Fish moved down under the noise effect in 10 times faster than at their daily vertical migration. The experimental data on walleye pollock density change under influence of passing fishing vessel are compared with the modeling results. Estimations of catchability coefficient for the accounting trawl РT/TM 57/360 are corrected taking into account the depth of trawling. The corrected coefficients of catchability for walleye pollock vary from 0.01 at the sea surface to 0.85 at the depth equal to the distance of its reaction to the noise.