How joint trends in environmental conditions can affect the upstream
migration of diadromous fish in a large basin?
Abstract
Water temperature and river discharge are critical cues shaping
biological processes of aquatic organisms. However, climate change can
disrupt the duration and frequency of specific associations between
water temperature and discharge, potentially hindering processes such as
migration, reproduction or feeding. In this study over a large European
basin, we compiled long-term upstream fish passage data for three
diadromous fish species and time series of water temperature and current
velocity reconstructed using physically-based thermal and hydrological
models. We first identified days exhibiting high numbers of upstream
fish passages and their corresponding water temperature-current velocity
associations (defined as ”suitable days”). We then investigated trends
in occurrence of suitable days for the upstream migration of diadromous
fish over the period 1963-2019. Our results showed that the impacts of
climate change on days with suitable associations appear to be
species-specific. We found decreases in occurrence of suitable days for
the upstream migration of Atlantic salmon mainly in the southern part of
the basin for salmon migrating in spring and in the middle reaches
scattered across the basin for fall salmon. On the other hand, days with
suitable associations for upstream migration have predominantly
increased for allis shad and sea lamprey across the whole basin. This
study offers practical insights into how changing environmental
conditions have affected the upstream migration of three diadromous
species.