Three‐dimensional internal spatial structure of young‐of‐the‐year pelagic freshwater fish provides evidence for the identification of fish school species

Abstract

Active acoustic detection and characterization in three dimensions (3D) with multibeam sonars is a powerful technique for ecological studies of schooling fish. The alpine Lake Annecy provides ideal conditions for sampling fish with active acoustic methods: it has calm water, low species diversity, and the density of pelagic fish schools is high. We carried out investigations on the internal 3D morphological characteristics of young-of-theyear (Y-O-Y) pelagic fish schools, using high resolution multibeam sonar in the vertical plane. The objective was to discriminate between the two fish species that school in the lake: perch (Perca fluviatilis) and roach (Rutilus rutilus). To discriminate between these Y-O-Y fish species, we used only one characteristic of their internal spatial structure: the total number of vacuoles, defined as empty volumes inside the school, relative to the school volume. Two distinct linear relationships between school volume and the total number of vacuoles were determined. These two types were consistent with the proportions of the percentage occurrence of the two different species as obtained from pelagic trawl sampling in 2004. In 2008, perch was dominant (93%) in the lake, and only one relationship was detected: this relationship corresponded closely to the one in 2004 attributed to perch. Thus, we assume that the schooling behavior is a phenotypic expression that could be used for remote fish species identification.*Corresponding author: E-mail: patrice.brehmer@ird.fr AcknowledgmentsThis work was supported by the ANSON project (INRA, IRD, IFRE-MER), and we are grateful to the CRH (IRD, IFREMER, UM II; Sète) who provided facilities. The second survey was financially supported by the INRA EFPA department, under the grant 'Innovative Project.' The software used for sonar data extraction was developed during the EU project AVITIS. Special thanks to Yvon Guennegan (IFREMER; Sète) for his help during the first survey, Michel Colon for his help during the two surveys, and Nicolas Givaudan (INRA; Thonon) for previous data analyses. We also thank Marc Taquet (IFREMER; French Polynesia) who attempted to identify species by scuba diving during the 2008 survey. Finally, we are grateful to Keith Mutch of Marine Scotland for producing the 3D graphic.

Characterizing the three‐dimensional distribution of schooling reef fish with a portable multibeam echosounder

“…We used remote video to identify the fish species present in each survey. MBES are only suitable for identifying species of schooling fish when there is some prior knowledge or in situ validation of taxa-specific school characteristics (Guillard et al 2011;Innangi et al 2016). Therefore, to identify the dominant species present, we deployed a single remote camera deployment per survey at the center of the reef complex for 30 min.…”

“…Furthermore, as schools increase in size, individual fish are less aware of the overall distribution of their school and must base their movements and behavior on that of their more immediate neighbors (Paramo et al 2007). As a result, large schools tend to exhibit more heterogeneous density throughout their volume, and are composed of a complex arrangement of high density volumes or nuclei, and empty or low density volumes, also known as vacuoles (Guillard et al 2011).…”

“…If a grid cell contained fish in every layer, then the calculated school thickness derived using the sum method and the difference method would be equivalent. The sum method should be more robust to the presence of vacuoles (Fréon et al 1992;Paramo et al 2007;Guillard et al 2011), spatially overlapping schools or lone targets overlying schools (Fig. 5).…”

Advances in fisheries science through emerging observing technologies

“…However, accuracy and reliability are paramount when making biological measurements with acoustic sensors. During the last few decades, the main advance is the advent of multibeam (e.g., Guillard et al, 2011) and wideband (Demer et al, 2017) acoustic systems, although calibration and data treatment are still challenging with existing protocols (e.g., Perrot et al, 2018). Rapid advances in the miniaturization of acoustic sensors (transducers) and the improvement of batteries and computers allow them to be mounted on various mobile platforms, such as gliders, Autonomous Underwater Vehicles (Moline et al, 2015) and buoys (Brehmer et al, 2019a), thus rendering this sensing technology cost-e ective both in hardware and in deployment compared to traditional shipboard transducers.…”

Advancing Observation of Ocean Biogeochemistry, Biology, and Ecosystems With Cost-Effective in situ Sensing Technologies

“…There exists a wide range of transducers that deliver results of interest for marine scientists, fisheries, and conservation managers, including echosounder and sonar systems. During the last few decades, the main advance is the advent of multibeam (e.g., Guillard et al, 2011) and wideband (Demer et al, 2017; acoustic systems, although calibration and data treatment are still challenging with existing protocols (e.g., Perrot et al, 2014Perrot et al, , 2018Demer et al, 2015;Korneliussen et al, 2016;Eleftherakis et al, 2018).…”