Linking Flow Regime, Floodplain Lake Connectivity and Fish Catch in a Large River-Floodplain System, the Volga-Akhtuba Floodplain (Russian Federation)

River-floodplain systems are amongst the most productive—but often severely impacted—aquatic systems worldwide. We explored the ecological response of fish to flow regime in a large river-floodplain system by studying the relationships between (1) discharge and inundated floodplain area, with a focus on spatial and temporal patterns in floodplain lake connectivity, and (2) flood volume and fisheries catch. Our results demonstrate a non-linear relationship between discharge and floodplain inundation with considerable hysteresis due to differences in inundation and drainage rate. Inundation extent was mostly determined by flood volume, not peak discharge. We found that the more isolated lakes (that is, lakes with a shorter connection duration to the river) are located at higher local elevation and at larger hydrological distance from the main rivers: geographical distance to the river appears a poor predictor of lake isolation. Although year-to-year fish catches in the floodplain were significantly larger with larger flood volumes in the floodplain, they were not in the main river, suggesting that mechanisms that increase catch, such as increased floodplain access or increased somatic growth, are stimulated by flooding in the floodplain, but not in the river. Fish species that profit from flooding belong to different feeding guilds, suggesting that all trophic levels may benefit from flooding. We found indications that the ecological functioning of floodplains is not limited to its temporary availability as habitat. Refugia can be present within the floodplain itself, which should be considered in the management of large rivers and their floodplain

Modelling population effects of juvenile offshore fish displacement towards adult habitat

Recent studies of fish distribution patterns highlight shifts in the spatial distributions of particular life-stages. Focus has thus far been on changes in habitat use and possible drivers for these changes. Yet, small-scale shifts in habitat use of certain life stages may have profound consequences on population dynamics through changes in resource use and competition. To explore this, a conceptual stage-structured model was developed with 3 stages and 2 resources and allowing a move of large juveniles from the shallow to the deep habitat. Large juveniles compete with small juveniles in shallow waters and with adults in deeper waters. Alternative stable states occur, with one state dominated by small juvenile biomass and the other dominated by adult biomass.The model results show for both states that while large juvenile biomass responds to a change in time spent in the deep habitat, the biomass of small juveniles and adults is barely affected. Between the 2 states there is a profoundly different population response to increased fishing mortality. In the adult biomass dominated state, adult biomass is hardly affected while juvenilebiomass increases until population collapse, with increased fishing. In the small juvenile dominated state, adult and small juvenile biomass decrease, and large juvenile biomass increases. This state persists at much higher fishing mortality than the adult biomass dominated state. This study highlights that safeguarding nursery functions in a changing environment requires monitoring of juvenile life-stages in a range of habitats and a spatially adaptive management strateg

Uittrek schieraal gesloten gebieden

Schieraal migreert naar de Sargasso Zee om zich voort te planten. De aallarven drijven vervolgens met de stroming de Atlantische oceaan over naar Europa en verspreiden zich over de Nederlandse binnenwateren via b.v. de Nieuwe waterweg of de sluizen in de Afsluitdijk. De aal verblijft als rode aal vijf tot vijftien jaar in Nederland voordat de rode aal een transformatie tot schieraal ondergaat en weer naar de Sargasso Zee trekt om te paaien. De hoeveelheid uittrekkende schieraal vanuit Nederland is dus afhankelijk van de aanwas aan glasaal en de hoeveelheid natuurlijke (predatie, ziekte) en antropogene (gemalen, WKCs, visserij) sterfte gedurende het lange verblijf in de binnenwateren

Three-dimensional multi-source localization of underwater objects using convolutional neural networks for artificial lateral lines

This research focuses on the signal processing required for a sensory system that can simultaneously localize multiple moving underwater objects in a three-dimensional (3D) volume by simulating the hydrodynamic flow caused by these objects. We propose a method for localization in a simulated setting based on an established hydrodynamic theory founded in fish lateral line organ research. Fish neurally concatenate the information of multiple sensors to localize sources. Similarly, we use the sampled fluid velocity via two parallel lateral lines to perform source localization in three dimensions in two steps. Using a convolutional neural network, we first estimate a two-dimensional image of the probability of a present source. Then we determine the position of each source, via an automated iterative 3D-aware algorithm. We study various neural network architectural designs and different ways of presenting the input to the neural network; multi-level amplified inputs and merged convolutional streams are shown to improve the imaging performance. Results show that the combined system can exhibit adequate 3D localization of multiple sources

Inventarisatie van de belangrijkste knelpunten voor de uittrek van schieraal in Nederland

Bij de afname van de palingstand spelen migratiebelemmeringen zeker een rol. In de Nederlandse watersystemen zijn veel kunstwerken aanwezig, zoals gemalen, waterkrachtcentrales, stuwen en sluizen. Deze beïnvloeden zowel de intrekmogelijkheden voor de glasaal vanuit zee als ook de uittrekmogelijkheden van schieraal, vanuit het zoete water naar zee. In 2009 is er een overzicht van de belangrijkste migratieknelpunten voor paling in Nederland opgesteld, waarbij geen onderscheid is gemaakt tussen intrekproblemen voor glasaal en uittrekproblemen voor schieraal. Voor de beoordeling van aanvragen voor ontheffing van het gebruik van aalvistuigen voor schieraaloverzet in de gesloten tijd, is er vanuit het Ministerie van EZ behoefte aan een vernieuwde lijst met prioritaire migratieknelpunten voor schieraal. Op basis van de geschatte verliesposten schieraal is een top 58 lijst van knelpunten in Nederland opgesteld. De lijst wordt aangevoerd door beide stuwcomplexen met waterkrachtcentrales in de Maas, bij Lith en Linne. Ook het stuwcomplex met waterkrachtcentrale Amerongen staat in de top 12. Daarnaast bestaat een groot deel van de lijst uit knooppunten met een gemaal, voornamelijk boezemgemalen, die ofwel direct op zee uitkomen of op een rijkswater afwateren

Abundance patterns of six fish species in the shallow coastal zone in The Netherlands

Sand nourishment is an essential part of the long term flood defense strategy of the Dutch coast. A distinction can be made between beach nourishments and underwater nourishments. This report concerns underwater nourishments. Nourishments have ecological consequences that differ between species living in the shallow coastal zone. The objective of the study is to derive abundance patterns based on habitat suitability models for a number of selected fish species that live in the shallow coastal zone. Abundance patterns form the basis for an assessment of the effects of nourishments