Subaquatic Photogrammetry Helps Understanding Habitat Suitability for Juvenile Lamprey in Streams

Habitat modification in freshwaters is a dominant cause of lamprey population decline. While adult lampreys are well studied in the literature, we lack information on the ecology of larval stages. Larva, or ammocetes, require specific habitats for their development, but the key characteristics of microhabitats (substrate features, biological interactions) that influence lamprey larva remain poorly understood. The main objective of this study is to evaluate whether structure from motion photogrammetry can be used as a non‐destructive tool to predict the presence of larval lampreys in stream microhabitats, and how its predictive performance compares to models that include additional biological data. To complement the photogrammetric approach, we conducted surveys of macroinvertebrate communities to explore potential biological interactions influencing lamprey larvae. Despite challenging environmental conditions (e.g., high turbidity, low depth), we achieved a 63% success rate in generating 3D point clouds of habitat patches. The results obtained from photogrammetry suggest that the average thickness of surface features above the streambed (e.g., leaves, branches, pebbles) were positively correlated with the presence of lamprey larva. Our analyses of macroinvertebrate communities show that the presence of Ephemera is negatively correlated with the presence of lampreys. Additional analyses show that models with both biological and photogrammetric descriptors are more accurate at predicting ammocoetes presence in patches compared to those with photogrammetric descriptors alone. Although slightly less accurate (by 7.5%), the model based on photogrammetry alone offers the key advantage of being entirely non‐destructive and relying on standardized method, facilitating its consistent application for high resolution monitoring. With a few improvements, subaquatic photogrammetry can thus be used as a non‐destructive and high‐frequency approach to assess the habitat suitability for larva lamprey in streams.