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

Abstract

In recent years, due to an increased need for non-intrusive sampling techniques, hydroacoustics has attracted attention in fishery science and management. Efforts to promote standardisation are increasing the accuracy, efficiency, and comparability of this method. The European Water Framework Directive and the Standard Operating Procedures for Fisheries Hydroacoustic Surveys in North American Great Lakes has recommended that surveys be conducted at night. At night, fish usually disperse in the water column, thus allowing for single echo detection and subsequent accurate fish size estimation, while day-time schooling behaviour hampers the estimation of fish size. However, sampling during the day would often be safer and cheaper. This study analyses how fisheries hydroacoustic results differ between day-time and night-time surveys, using data from 14 natural temperate lakes of various size. Data collected during the day and night at two depth layers linked to thermal stratification were compared in terms of acoustic scattering strength, target strength, and biomass estimates. The results showed a significant correlation between day-time and night-time estimates, though biomass in the upper layer was biased for day-time surveys, mainly due to incorrect fish size estimates resulting from rare single echo detections and schooling behaviour. Biomass estimates for the lower depth layer did not significantly differ between the two diel periods. Thus, this study confirms that hydroacoustic sampling in temperate lakes should be performed at night for accurate fish stock biomass estimates.

An Assessment of Hydroacoustic and Electric Fishing Data to Evaluate Long Term Spatial and Temporal Fish Population Change in the River Thames, UK

“…Hydroacoustic surveys on the Rivers Trent and Thames [21,22] observed a significant difference in the spatial distribution of fish between day and night. This variation has also been established in lake environments [57,58]. Applying this evidence, our study followed the best practice approach, conducting all surveys between one hour after dusk and one hour before dawn.…”

Hydroacoustic Autonomous boat for Remote fish detection in LakE (HARLE), an unmanned autonomous surface vehicle to monitor fish populations in lakes

“…The survey was conducted on 25 September 2017, in agreement with the standards (Parker-Stetter et al 2009;CEN 2014) and when the dominant fish populations are in open water and structured based on the thermocline. This study was performed at night when the fish are dispersed (Girard et al 2020) and away from the bottom to locate the optimal temperature (Mehner et al 2010), as recommended by the standardization procedures (Parker-Stetter et al 2009;CEN 2014). The study was performed under light air conditions (maximum wind speed of 5.5 km h −1 ).…”

Spatial and temporal variations of Limnothrissa miodon stocks and their stability in Lake Kivu

“…Hydroacoustic sampling is usually carried out at night due to fish behavior because fish are scattered and individual size estimations are possible, in contrast to the daytime, when fish are mainly in schools or close to the bottom (Coll et al, 2007;Girard et al, 2020;Prchalová et al, 2003). However, as the historical surveys were performed during the daytime (Guillard et al, 2012;Lamboeuf, 1991), the hydroacoustic surveys in the present study were performed during this photoperiod between 05:00 and 16:00.…”