Downstream migration and mechanisms of dispersal of young fish in rivers

Abstract

Downstream migration (DSM) of young fish has traditionally been considered a passive process. A review of studies of the patterns and mechanisms of DSM showed that it met the main criterion for migration: that animals move between well-defined habitats according to a predictable schedule. During DSM, fish often leave the habitat in which they reside (inshore zone) and enter a migratory habitat (main channel). DSM is manifested at a seasonal or diel scale and in species-specific spatial distribution patterns. According to our "dispersal with low dilution" hypothesis, the supposed adaptive value of DSM is due not only to dispersal but also to maintenance of aggregations and synchronization of migratory activity. Temporal and spatial peaks of migration promote efficient intraspecific interactions, such as shoaling, and the integrity of populations. We conclude that migratory behaviour is most successful in habitats with optimum complexity and that the influence of behaviour on DSM is most important at key periods and sites (twilight windows and interfaces between habitats).Résumé : L'avalaison de jeunes poissons a traditionnellement été considérée comme étant un processus passif. Un examen des études des motifs et mécanismes d'avalaison montre qu'elle répond au principal critère d'une migration, soit que les animaux se déplacent entre des habitats bien définis selon un cadre temporel prévisible. Durant l'avalaison, les poissons quittent souvent l'habitat où ils résident (zone côtière) et entrent dans un habitat migratoire (chenal principal). L'avalaison se manifeste à une échelle saisonnière ou journalière et selon des motifs de répartition spatiale propres à chaque espèce. Selon notre hypothèse de « dispersion avec peu de dilution », la valeur adaptative supposée de l'avalaison résulte non seulement de la dispersion, mais également du maintien de groupements et de la synchronisation de l'activité migratoire. Les pointes de migration temporelles et spatiales favorisent des interactions intraspécifiques efficientes, comme le regroupement en bancs, et l'intégrité des populations. Nous concluons que le comportement migratoire a le plus de succès dans des habitats de complexité optimale et que l'influence du comportement sur l'avalaison est la plus importante dans des périodes et des sites clés (fenêtres crépusculaires et interfaces entre habitats). [Traduit par la Rédaction]

A study on fish eggs and larvae drifting in the Jirau reservoir, Brazilian Amazon

“…As stated by Pavlov and Mikheev [54], during dispersal, the local densities of migrating fish may become low. This could hinder essential interactions as group formation.…”

Diel migration pattern of pink salmon fry in small streams

“…Several salmonids perform downstream migration at night (Hintz & Lonzarich, 2012; Johnston, 1997; Pavlov & Mikheev, 2017). In general, except for some large rivers, high turbidity conditions and polar‐day conditions, the fry of the pink salmon Oncorhynchus gorbuscha perform downstream migration at night (Ali & Hoar, 1959) and finish their migration overnight (Heard, 1991); however, since the previous studies about diel migration of pink salmon have been conducted in rivers of various sizes ( e.g ., Kirillov et al ., 2018; Neave, 1955; Pavlov et al ., 2015), these studies have shown different results between rivers or surveys.…”

“…Therefore, our study shows that individuals emerging in small streams quickly migrated to the sea. Other salmonids show nocturnal downstream migration: the brown trout Salmo trutta , coho salmon O. kisutch , Atlantic salmon S. salar and rainbow trout O. mykiss (Hintz & Lonzarich, 2012; Johnston, 1997; Pavlov & Mikheev, 2017). Nocturnal migration may be a strategy to avoid predation (Ibbotson et al ., 2011; Johnston, 1997; Kennedy et al ., 2018).…”

Identifying turbulence features hindering swimming capabilities of grass carp larvae (Ctenopharyngodon idella) through submerged vegetation

“…A key aspect of improving control and monitoring of grass carp larvae in streams relies on understanding their behaviour from hatching until the development of their swimming capabilities. While there are several biotic factors that might affect larval drift (e.g., Lechner et al 2016;Pavlov and Mikheev 2017, and references therein), our study focuses on the larval response to hydrodynamic features. Larval response to flow conditions is dependent on the species and their developmental stage (Pavlov et al 2008;Lechner et al 2014).…”