Including 38 kHz in the standardization protocol for hydroacoustic fish surveys in temperate lakes

Abstract

Hydroacoustics has become a requisite method to assess fish populations and allows to describe the relationships of fish with other elements of the aquatic ecosystem. This nonintrusive method is currently an integral part of the sampling procedures recommended for fish stock assessment by the Water Framework Directive and has been standardized by the European Committee for Standardization [CEN (2014) CSN EN 15910 ‐ Water quality ‐ Guidance on the estimation of fish abundance with mobile hydroacoustic methods, Category: 7577 Water quality. Biological.]. In Europe, hydroacoustic surveys are performed in freshwater using different frequencies. Consequently, there is a need to evaluate if survey results can be compared. This study aimed to carry out in situ comparisons at the 38 kHz frequency (noted f) with two other commonly used frequencies, 70 and 200 kHz. The 38 kHz frequency has seldom been compared with other frequencies in freshwater although it is widely used worldwide, especially in the Great Lakes of North America and in Sweden. In 2016, hydroacoustic data were acquired in Lakes Annecy and Bourget using methods validated in previous studies that compared the frequencies 70, 120 and 200 kHz. This study showed similar density and biomass estimations as a function of frequency, density(f) and biomass(f), between the frequencies studied for low to moderate fish densities. For higher fish densities, the results were more variable and need to be verified. Fish density(f) and biomass(f) estimations sometimes exhibit differences between frequencies, which is not fully in agreement with theoretical calculations. The aim of this study was to evaluate frequency comparisons in practise. However, if the differences on acoustic metrics, density(f) or biomass(f) between frequencies were occasionally statistically significant, the differences were small enough to be considered negligible for fish population management. These analyses led to better knowledge of the responses from fish in temperate lakes for the studied frequencies. Our findings should be considered when revising the CEN standard.

Vessel Avoidance Response: A Complex Tradeoff Between Fish Multisensory Integration and Environmental Variables

“…Detailed in situ target strength studies are called for, like those performed by Gauthier and Rose (2002) using a tow system deployed at various depths combined with a classical, hull-mounted echosounder, to obtain accurate data about the effect of the SPL of the platform on the TS values (i.e., the TS delivered by the tow system are supposed to not be directly under the vessel perturbation influence). Some works on fish populations with swimmblader have shown that there is no significant difference in the volume backscattering strength and TS measurements measured in situ at 38, 70, 120 and 200 kHz (Guillard et al 2014;Mouget et al, 2019). In our study, the TS distributions were also found similar between our 38 and 70 kHz measurements from the two platforms.…”

“…Although the difference in frequency has no or few impact on the geometry of the detections, it can have a significant effect on the backscattering of the target, and especially on fish target strength (Horne, 2000). (Mouget et al, 2019) following Guillard et al (2014) protocol have shown that there is no significant difference between the main hydroacoustic metrics from fish with swim bladder using 38 kHz and other usual frequencies as 70 and 120 kHz. The authors concluded to a similarity of density and biomass estimation measurements between 38 and 70 kHz for fish with a swim bladder.…”

Comparisons of day-time and night-time hydroacoustic surveys in temperate lakes

“…Furthermore, a standardised main axis (SMA) test was performed according to Warton et al (2006). This test has previously been used to compare hydroacoustics data from two different situations (Godlewska et al, 2011;Mouget et al, 2019). This procedure is appropriate to enhance and complete linear regression, and when measurement error is unknown (Warton et al, 2006), which is the case for acoustic metrics.…”

Limits for <i>Coregonus migratorius</i> (Georgi, 1775) catches and likely ecological effects

“…В мировой практике оценки рыбных запасов приоритет отдается использованию гидроакустических методов [11][12][13][14]. Данные методы апробированы и адаптированы к условиям исследования запасов омуля в озере Байкал [6], они продолжают совершенствоваться [15][16][17] и остаются перспективным направлением исследований [18].…”