Combining green LiDAR bathymetry, aerial images and telemetry data to derive mesoscale habitat characteristics for European grayling and brown trout in a Norwegian river

Knut Alfredsen,Torbjørn Forseth,Jon Museth,Håkon Sundt

doi:10.1007/s10750-021-04639-1

Knut Alfredsen, Torbjørn Forseth + Show 2 more

Open Access

https://doi.org/10.1007/s10750-021-04639-1

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Abstract

While many studies provide microscale relationships between fish and habitat characteristics, studies covering longer river reaches are scarce. Modern remote sensing techniques may enable new and effective ways of mapping and assessing mesoscale habitat characteristics. Using green LIDAR-derived bathymetry and hydraulic modelling, we tested how mesoscale depth and velocity were related to fish counts of adult European grayling (Thymallus thymallus L.) and brown trout (Salmo trutta L.) in 500 m river sections in three separate periods during the year. Using riverbank sinuosity from aerial images and a Froude number-based index from the hydraulic model as proxies for mesoscale spatial and hydraulic heterogeneity, we tested for temporal correlations with river section fish counts of adult European grayling and brown trout. Results showed that mesoscale mean depth and velocity were correlated to period fish counts of adult European grayling. Using mixed model analysis we found that riverbank sinuosity and the Froude number-based index were significantly correlated with river section occurrence of adult European grayling during spawning. The results can be used to assess how flow-induced changes and channel adjustments at the mesoscale level can influence access to and use of relevant habitats in rivers occupied by European grayling and brown trout.

Highlights

River regulation can affect relevant habitats for aquatic biota through factors like fragmentation, channelization, and flow modification (Warren et al, 2015; Van Leeuwen et al, 2018; Hellstrom et al, 2019)
Using mixed model analysis we found that riverbank sinuosity and the Froude number-based index were significantly correlated with river section occurrence of adult European grayling during spawning
We were not able to test the sensitivity of river section length on the model variables and results, we found significant correlations between habitat characteristics and fish occurrence on the scale chosen in this study

Summary

Introduction

River regulation can affect relevant habitats for aquatic biota through factors like fragmentation, channelization, and flow modification (Warren et al, 2015; Van Leeuwen et al, 2018; Hellstrom et al, 2019). As habitat requirements in many cases are seasonal or life stage dependent (e.g., for salmonid fish), mitigation efforts in regulated rivers should, if possible, be based on ecological and physical elements across spatial and temporal scales. The combined use of ecological and physical data have been at the heart of flow mitigation efforts in regulated rivers for decades (Richter et al, 1997; Bovee et al, 1998). To propose relevant mitigation and conservation efforts in rivers one must conclude with a certain level of confidence on how the physical environment influences the ecological status of local key species. Some studies have observed significant connections between physical instream characteristics and ecological elements (Maddock et al, 2013), Petts et al (2006) argued for an increased integration of hydraulics and ecology in conservation and mitigation management settings. Some studies have observed significant connections between physical instream characteristics and ecological elements (Maddock et al, 2013), Petts et al (2006) argued for an increased integration of hydraulics and ecology in conservation and mitigation management settings. Hardy (1998) addressed the need to develop a range of model tools, in close collaboration between biologist, engineers and resource managers

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