Density dependent attributes of fish aggregative behaviour

Abstract

Grouping behaviour, as fascinating as it is unclear, has lately drawn the attention of numerous researchers. While most of the authors focused their work on a mechanistic approach to the matter of schooling, this study explores the issue from a population point of view. Present camera observation study on the fish community carried out in the epipelagic habitat of a European temperate reservoir in the Czech Republic explored the relationship between density and aggregative features of predominantly cyprinid fish stock. Results demonstrated that schooling behaviour is triggered by the ‘critical density’ of fish in the habitat. School size as well as counts of schools and proportion of schooling individuals increased with the density of fish. Counts of clusters (observed units in time, including singletons, pairs and schools) and cluster size, on the other hand, showed a slowing tendency to increase. The slower increase implies the tendency of fish for not being frequent but rather to create larger groups. Altogether, our findings suggest that fish density is a triggering factor in the formation of large fish schools. As the tendency of cyprinid species for school formation could be an evolutional advantage responsible for dominance in later succession phases of water bodies, we suggest that more in situ studies should be encouraged for the proper understanding of the ecological interactions that drive the structure of aquatic ecosystems and for ensuring unbiased assessment.

Species‐specific schooling behaviour of fish in the freshwater pelagic habitat: an observational study

“…Nonetheless, schooling tendency varied between species with diverse proportions of schooling and non‐schooling individuals as well as school sizes and willingness to form heterospecific groups. The proportions of fish in pairs were similar among three schooling species (roach, bream and perch) and did not significantly change with increasing density of fish (Holubová et al ., 2019b). The low presence of pairs implies that they present just “stepping stones” towards schools.…”

Distribution of sturgeon in the River Irtysh

“…The study of the influence of environmental characteristics and their dynamics makes it possible to determine the sections of aggregations for aquatic organisms, facilitating their registration and monitoring, including rare and endangered fish species (Bogdanov & Mel'nichenko, 2011, Thayer et al, 2017Andrews et al, 2020;). The formation of aggregations of fish can be influenced by the features of the bottom morphology, hydrological characteristics (Pavlov et al, 2010;Bogdanov & Mel'nichenko, 2011;Westrelin et al, 2017;Thayer et al, 2017), availability of prey (Holubová et al 2019).…”

Fluctuations in pelagic fish density linked to ambient conditions

“…As density affects the formation of schools, the presence of the fish schools in the pelagic habitat should fluctuate similarly (De Kerckhove et al, 2015;Holubová et al, 2019). Fish aggregate in schools predominately during the day using vision as the primary sense to maintain the school (Whitney, 1969) and disperse during twilight as the light level decreases and individuals cannot visually maintain contact with shoaling neighbours.…”

“…Fish aggregate in schools predominately during the day using vision as the primary sense to maintain the school (Whitney, 1969) and disperse during twilight as the light level decreases and individuals cannot visually maintain contact with shoaling neighbours. However, it has been noted that the schooling tendency depends on the number of conspecific fish in the habitat (Holubová et al, 2019). Species of the pelagic habitat not rarely incline to socializing by means of group living (Fréon & Misund, 1999).…”

“…Species of the pelagic habitat not rarely incline to socializing by means of group living (Fréon & Misund, 1999). Although aggregations are particularly numerous and dense in marine habitats (Makris et al, 2009), freshwater fish tend to form much smaller assemblages (e.g., Holubová et al, 2019;Russell et al, 2004). Predator occurrence is an important factor in the spatial structuring of aquatic inhabitants (Jackson et al, 2001) and can affect the fish distribution (Werner & Hall, 1988).…”