Migrations of Young Fish in Anthropogenically Transformed Rivers: Responses of Cyprinids and Percids to Ecological Filters and Barriers

Victor N Mikheev,Dmitrii S Pavlov,Vasilii V Kostin

doi:10.3390/w13091291

Abstract

Downstream migration (DSM) of larvae and fry is an important phase of the life cycle of fish as it allows them to disperse, and it increases the size and diversity of the populations via them extending rearing grounds, exchanging genes, and avoiding competition and cannibalism. Two numerous and diverse fish families of the Eurasian rivers, Cyprinidae and Percidae, are well adapted to the conditions of the riverine continuum. Having said that, the regulation of rivers (construction of dams and water reservoirs) drastically changes their hydrology and topography. In this work, we argued that novel conditions of transformed river habitats influence the DSM of young cyprinids and percids in different ways. The published results on fish DSM and spatial distribution in nine European reservoirs (Russia, Kazakhstan, Czech Republic, Bulgaria) in comparison with untransformed rivers were reanalyzed from the viewpoint of this argument. Changes in the major characteristics of DSM of young cyprinids and percids, i.e., intensity, diel (24-h period), and seasonal patterns of migrations, as caused by anthropogenic transformation of the rivers, were revealed. We found that the novel ecological barriers and filters associated with different parts of water reservoirs differently influence the lateral and longitudinal movements, and the diel and seasonal dynamics of DSM of cyprinids and percids. These effects result in significantly more intensive emigration of young percids compared to cyprinids from reservoirs with deep-water intakes. At the scale of the whole regulated river, the morphological complexity (topography) of the reservoir plays a pivotal role in controlling the intensity of the DSM of young fish. Measures for the conservation and restoration of percid and cyprinid populations should be different.

Highlights

Most organisms disperse from a natal/breeding site, which enables the exploitation of spatially and temporally variable resources in continually changing natural habitats [1,2]
Similar patterns of downstream migrations of the two most abundant groups of European riverine fish, cyprinids and percids, differ in the spatial distribution of migrating larvae [11]. We expect that such differences, which under conditions of natural rivers do not lead to differences in the main patterns of Downstream migration (DSM) of cyprinids and percids, may cause a significant differentiation under the conditions of regulated rivers
The obtained results suggest that patterns of downstream migration of cyprinid and percid fishes are strongly influenced by a novel physical template created by river regulation

Summary

Introduction

Most organisms disperse from a natal/breeding site, which enables the exploitation of spatially and temporally variable resources in continually changing natural habitats [1,2]. It appears that the ability of young percids and cyprinids to efficiently use structured habitats of natural rivers and migrate freely along the whole river continuum is similar With this in mind, does their migratory behavior change in regulated rivers where fish should overcome vast open water and dams? Because of the similarity of the main characteristics of the DSM of young cyprinids and percids in natural rivers, we may expect similar patterns of their migration both within water reservoirs and downstream of dams. Similar patterns of downstream migrations of the two most abundant groups of European riverine fish, cyprinids and percids, differ in the spatial distribution of migrating larvae [11] We expect that such differences, which under conditions of natural rivers do not lead to differences in the main patterns of DSM of cyprinids and percids, may cause a significant differentiation under the conditions of regulated rivers. InInccoonnttrraasstt to tthheesseeaassoonnaallppatattetrenrns sofotfhtehceoncocenncternattriaotnioonf mofigmraingtrsanintsthine nthateunraalturirvaelr, rwivhere,rwe thheereotnhley opnrolynpouronncoeudnpceadkpweaaks wobaseorbvseedrvinedJuineJuannedasnmdaslmlearlpleerapkefaokr fcoyrpcryinpirdi-s niindsJuinlyJu(Flyig(uFrigeu3r)e, 3in), irnegreuglautleadtedrivrievresr, sb, rboraodaderermmaaininsseeaassoonnaall ppeeaakkss ((JJuunnee––JJuullyy)) wweerree rreeccoorrddeeddininbobtohthfafmamiliielsieosfoffisfihs(hFi(gFuirgeu6re). 6M).orMeoovreero,vaelro, waelrobwuetrsbtiulltcsotnilslidcoernasbidleercaobnl-e cceonntrcaetniotrnatoiof nmoifgmraingtrsawntasswraescorredcoedrddedurdinugrinthgethreesrtesotfotfhteheyeyaera,re, sepspeceicailallylyfoforrppeerrcciiddss (F(Figiguurree66))..AAssigignnifiificcaannttaammoouunnt tooffmmigigrraatitninggYYOOYYggrroowwnnppeerrccididsswwaassrreeccoorrddeedddduurriinngg ththeeaauututummnn––wwininteterrppeeriroiodd. .TThhisismmayaylelaedadtotoaassuubbsstatanntitaial llolossssooffaavvaaluluaabbleleppoorrttiioonnooff ppeerrccididppooppuulalattioionnss

Emigration through the Power Plants and Shipping Locks

III IV V VI VII VIII IX X XI XII Months

Conclusions