This dataset is for the report titled "Mitigation of inland navigation effects on biodiversity by longitudinal training dams". The report focuses on assessing the effects that inland navigation has on the ecology of the river Waal and the mitigation of these effects by the three novel longitudinal training dams (LTDs) constructed in 2015 as a pilot project by Rijkswaterstaat (RWS). Moreover, fish and abiotic conditions monitoring performed in the period 2016 – 2020 was continued during 2021. Several techniques were used to measure the effects of ships on biodiversity, including the monitoring mussel behavior through Hall sensors, seine net fishing to assess fish densities, the use of hydrophones to measure underwater sound levels and remote sensing techniques to evaluate the ambient conditions at the LTD shore channels during 2020 and 2021.

This report aims at answering the following research questions: 1) How do ship effects differ between the LTD shore channels and groyne fields? 2) Does the behaviour of mussels differ between habitats exposed and protected to ship effects? 3) What EPT species are using the LTD shore channels as habitats? 4) Do dreissenids occur more often in wave exposed or protected areas of the LTDs themselves? 5) Do the young of the year fish in the LTD shore channels react to the introduction of sound from inland navigation? 6) How did fish densities differ between the LTD shore channels and groyne fields during high river discharges in 2021? 7) What were the patterns of erosion in the shore channels and how did the shoreline length change in the period 2019-2020?

METHODS SUMMARY: 1. Fish density shore channels: After the construction of the LTDs, several monitoring techniques have been used to assess the fish biodiversity and densities in the LTD shore channels. In this study we focus on data collected throughout 2021 using seine nets in the Dreumel and Ophemert shore channels and reference groynes. The fork lengths of each fish caught were recorded as well as species and sampled surface area. 2. Underwater sound and freshwater fish: Monitoring of fish with a seine net was done in the littoral zone at night during two campaigns in 2021 including high and low river discharges. The monitoring entailed the introduction of an underwater speaker to play pre-recorded sounds of inland navigation that passed in a nearby groyne field to quantify the response of fish densities. This sampling was done in the Ophemert shore channels with controls taking place in both the shore channel and reference groyne fields nearby. 3. Mussel behaviour: To assess whether there is a significant difference in habitat quality for freshwater mussels between the Dreumel shore channel and a nearby groyne field their behaviour was measured with a Hall sensor to quantify their level of activity (i.e. closures). 4. Ship effects: Sensors were deployed to assess parameters such as water level, light intensity underwater, temperature, sound and acceleration.