New way to investigate fish density and distribution in the shallowest layers of the open water
Introduction
Open water represents the largest volumes of larger lakes and reservoirs. Quantitative fish sampling of these volumes still represents a challenge (Kubečka et al., 2012). Hydroacoustics is an obvious option for covering large areas without disturbing fish and causing sampling-related mortality. However, most fish utilize shallow water closest to the surface (Jarolím et al., 2010; Kubečka and Wittingerová, 1998; Vašek et al., 2009) and it is difficult to obtain sound estimates with conventional downward-looking acoustics due to nearfield near transducer and narrow beam width close to water surface. Only a small proportion of the fish stock can be assessed with downward-looking echosounding in eutrophic waters (Kubečka and Wittingerová, 1998). Another option for pelagic fish assessment, the horizontal beaming is influenced by unwanted interference of multipath reflections (Balk et al., 2017). Therefore, reliable quantitative assessments of fish community in the shallowest layers of the open water are rare.
An alternative approach of using a mobile upward-looking surveying was developed to mitigate this unsatisfactory situation. This approach was shown to provide very clear data recordings of small fish and even invertebrates (Baran et al., 2017 and 2019). Upward-looking echosounding has been used previously for surveying of fish populations at fixed location (Axenrot et al., 2004; Čech and Kubečka, 2002; Jarolím et al., 2010), but rarely in mobile mode (but see Probst et al., 2009; Říha et al., 2017; Grow et al., 2020).
Upward-looking surveys are more reliable when done at night (Baran et al., 2017 and 2019). During the day Baran et al. (2017 and 2019) observed that fish are likely to react to the survey vessel (see also Rakowitz et al., 2012 and Muška et al., 2013). Daytime is also not a suitable period for surveying because most reservoir fish perform sinusoidal swimming to search for zooplankton more efficiently (Čech and Kubečka, 2002; Jarolím et al., 2010). While performing sinusoidal swimming, the fish body aspect exposed to the upward-looking transducer is very difficult to define as the fish can have any aspect within the range of + 30 to –30 degrees tilt (Čech and Kubečka, 2002) leading to poorly defined TS to fish length relationships.
In this study, we explored whether night mobile upward-looking acoustic surveys represent a reliable tool for community assessment of yearling-and-older fish. During the summer season in the Římov Reservoir (Czech Republic), we used the upward-looking acoustics and CEN multimesh gillnets simultaneously to enable comparison of size distributions obtained from the two gears. CEN multimesh gillnets (CEN, 2015) are relatively free of size selective biases for a wide range of fish sizes larger than 8 cm (Prchalová at al., 2009) and smaller than 30 cm standard length (Šmejkal et al., 2015). If the two size distributions agree, we suggest that large fish do not differentially avoid our upward-looking acoustic system. Further, we analyzed vertical micro-distribution of fish within the uppermost 3 m of the water column.
Section snippets
Study area
This study was conducted in the Římov Reservoir (48°50′N, 19°30′E, 471 m above sea level, Fig. 1), 170 km south of Prague, Czech Republic. The reservoir was constructed on the Malše River in 1978. It is a canyon-shaped reservoir with a length of 12 km (on original riverbed), a maximum volume of 33 × 106 m3, a surface area of 2.1 km2, and an average and maximum depth of 16 m and 43 m, respectively. The trophic state of the reservoir is mesotrophic to eutrophic with well-developed thermal
Comparison of total catches and records
A total of 699 fish larger than 8 cm were caught in the 36 gillnet sets (451 bleak, 84 common bream, 120 roach, 26 European perch (Perca fluviatilis) and 18 individuals of other species). During hydroacoustic surveys, 463 targets bigger than 8 cm (−45.5 dB) were recorded and 15,526 m3 of water was sampled.
Vertical fish distribution
In pelagic gillnets we captured between 55–71 percent of all caught fish within 1 m of the surface (Fig. 3). The percentages of acoustic targets detected in the 0.3–1 m depth layer represented
Discussion
The current study demonstrates that mobile upward-looking acoustic surveys have potential to be a reliable tool in fish community assessment in the epilimnion of stratified lentic waters. Most studied parameters of the acoustic assessment including overall size distribution, and vertical distributions corresponded well with the same parameters obtained by gillnets.
Both methods revealed that fish had an affinity to the topmost 1 m of the water column. Given this vertical distribution, it is
Conclusions
The new sampling method circumvents to a large extent the disadvantages of horizontal and downward looking hydroacoustic transducers when sampling near the surface (upper 3 m). We found majority of fish to occupy water layer very close to the surface (0.3−1 m) and these would be mostly missed by down- or side-looking acoustic sampling. Comparison with gillnets showed that upward-looking records provided similar fish size distribution. Evaluation of upward-looking mobile echo sounding could be
CRediT authorship contribution statement
Roman Baran: Conceptualization, Data curation, Formal analysis, Writing - original draft, Writing - review & editing. Petr Blabolil: Data curation, Formal analysis, Investigation, Visualization. Martin Čech: Conceptualization, Investigation. Vladislav Draštík: Data curation, Formal analysis, Investigation, Software, Supervision. Jaroslava Frouzová: Supervision, Validation. Michaela Holubová: Investigation. Tomáš Jůza: Conceptualization, Investigation. Ievgen Koliada: Investigation. Milan Muška:
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We thank Dagmar Kubečková – Synková, A.D. Jayasinghe, L. Kočvara and Z. Prachař for help with data collection, as well as the FishEcUteam(www.fishecu.cz) for critical reading of the manuscript.
The work was supported by ERDF/ESF project Biomanipulation as a tool for improving water quality of dam reservoirs (No. CZ.02.1.01/0.0/0.0/16_025/0007417) and project CZ.1.05/3.1.00/10.0214 technology transfer both administrated by the Ministry of Education, Youth and Sports of the Czech Republic. R.
References (36)
- et al.
Surface-induced errors in target strength and position estimates during horizontal acoustic surveys
Fish. Res.
(2017) - et al.
Reconstructing the build-up of a pelagic stickleback (Gasterosteus aculeatus) population using hydroacoustics
Fish. Res.
(2019) - et al.
Target strength of some European fish species and its dependence on fish body parameters
Fish. Res.
(2005) - et al.
Spatial and vertical bias in down-looking ship-based acoustic estimates of fish density in Lake Superior: directional acoustics
J. Great Lakes Res.
(2020) - et al.
Acoustic scattering from a larval insect (Chaoborus flavicans) at six echosounder frequencies: implication for acoustic estimates of fish abundance
Fish. Res.
(2006) - et al.
Horizontal beaming as a crucial component of acoustic fish stock assessment in freshwater reservoirs
Fish. Res.
(1998) - et al.
Fish sampling with active methods
Fish. Res.
(2012) - et al.
Size selectivity of standardized multimesh gillnets in sampling coarse European species
Fish. Res.
(2009) - et al.
Fish activity as determined by gillnet catch: a comparison of two reservoirs of different turbidity
Fish. Res.
(2010) - et al.
Hydroacoustic observations of surface shoaling behaviour of young-of-the-year perch Perca fluviatilis (Linnaeus, 1758) with a towed upward-facing transducer
Fish. Res.
(2009)
Use of high-frequency imaging sonar (DIDSON) to observe fish behaviour towards a surface trawl
Fish. Res.
Vertical distribution of alewife in the Lake Onatario offshore: implications for resource use
J. Great Lakes Res.
Fish orientation along the longitudinal profile of the Římov reservoir during daytime: consequences for horizontal acoustic surveys
Fish. Res.
Diel variation in gillnet catches and vertical distribution of pelagic fishes in a stratified European reservoir
Fish. Res.
Can pelagic forage fish and spawning cisco (Coregonus artedi) biomass in the western arm of Lake Superior be assessed with a single summer survey?
Fish. Res.
Diel patterns in pelagic fish behaviour and distribution observed from a stationary, bottom-mounted, and upward-facing transducer
ICES J. Marine Sci.
A novel upward-looking hydroacoustic method for improving pelagic fish surveys
Sci. Rep.
Quantification of chaoborus and small fish by mobile upward-looking echosounding
J. Limnol.
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2022, Fisheries ResearchCitation Excerpt :It has been standardized for lake surveys both on the North American continent for the Great Lakes (Parker-Stetter et al., 2009) and on the European continent related to the Water Framework Directive (CEN, 2014; Draštík et al., 2017). Used for several decades and recognized today as a reliable method (Rudstam et al., 2012), fishery acoustics is commonly used in scientific studies and monitoring surveys in lakes (Baran et al., 2021; Godlewska et al., 2016; Pollom and Rose, 2016; Wheeland and Rose, 2016). During the last decades, in Europe, the most frequently scientific echo-sounders used for research and monitoring surveys, both in freshwater and marine environments, are from the Simrad company (Simrad Kongsberg Maritime AS, Horten, Norway).