Recruitment dynamics of rheophilic fish in floodplain systems in relation to habitat complexity and its temporal variability (River Rhine, the Netherlands)

Background

The River Rhine has been extensively modified throughout history, which resulted in the decline or loss of many of its original flora and fauna. Despite recent changes in ecological perception and the subsequent positive changes to water quality and habitat variability, the ecological quality of the River Rhine is still poor. Especially the recovery of rheophilic fish species, an indicator for good ecological quality, remains below expectations. We expect that the (slow) recovery pattern of these rheophilic fish populations is mainly caused by insufficient presence and accessibility of habitats that function as spawning and nursery area for rheophilic fish.

Objectives

The main objective of this project is to assess the temporal and spatial use of diverse habitats by juvenile rheophilic fish in the aquatic-terrestrial transition zones in the floodplains along the lower river Rhine. The project focusses on the underlying processes of recruitment dynamics of rheophilic fish in relation to habitat complexity and food availability.

Methodology

Fieldwork activities are focussed on simultaneously sampling of juvenile fish populations and a broad range of environmental variables that may contribute to recruitment dynamics. In the first fieldwork year (2017) 59 locations were sampled. In the analysis of this dataset, three potentially interesting locations for rheophilic fish recruitment will be selected and sampled in more detail and more frequently in 2018. A similar procedure will be used for 2019 and 2020. A combination of different techniques (hoop/larval nets, seine nets and fish traps) will be used to assess recruitment dynamics at fine spatial and temporal scales throughout the spawning and nursery season. These three potentially interesting floodplain systems will be studied for 3 years (2018-2020) with help of MSc students and interns and will be monitored on a (bi-)weekly basis from March until October, the ‘nursery season’ for (rheophilic) fish in the river Rhine. In addition, a habitat model will be developed to predict rheophilic fish recruitment in varying environmental circumstances.

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