Environmental influences on the phenology of immigrating juvenile eels over weirs at the tidal limit of regulated rivers

• Published in: Hydrobiologia 2024-10, Vol.851 (18), p.4439-4458
• Main Authors: Boardman, Rose M., Pinder, Adrian C., Piper, Adam T., Gutmann Roberts, Catherine, Wright, Rosalind M., Britton, J. Robert
• Format: Article
• Language: English
• Subjects: Anguilla anguilla; Annual precipitation; Annual variations; Biomedical and Life Sciences; catadromous fish; Catadromous species; Climate change; Climate prediction; Ecology; eel; Eels; Endangered species; England; Environmental conditions; Fresh water; Freshwater & Marine Ecology; juveniles; Life cycle; Life Sciences; Marine fishes; Migrations; Phenology; Primary Research Paper; Regulated rivers; River regulations; Rivers; Sea surface temperature; temperature; Weirs; Zoology
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1007/s10750-024-05596-1

Recruitment of the catadromous and critically endangered European eel Anguilla anguilla in Europe has declined substantially since the 1980s, with considerable knowledge gaps remaining in many aspects of their life cycle. The aim was to assess eel migration phenology in three regulated rivers in England between 2009 and 2019 through analyses of eel numbers using passes at their tidal limits, with calculation of the annual timings of migration initiation (10% of all eels passed, T 10 ), peak (50%, T 50 ) and conclusion (90%, T 90 ). Across the three rivers, T 10 varied between Julian Day (‘Day’) 94 and 173. Years of earlier T 10 had significantly earlier T 50 , where T 50 varied between Day 105 and 200. The considerable inter-annual variability in migration timings was associated with environmental variables; earlier T 10 and T 50 occurred in years of warmer river temperatures (RTs) and cooler sea surface temperatures (SST), and in years where RTs were higher than SSTs. No environmental variables were significant predictors of T 90 . These results indicate that whilst there is annual variability in the timing of eel migration initiation and peak into freshwaters, this variability is predictable according to differences in environmental conditions. As many of these conditions associated with annual variability in temperature and precipitation then climate change has the potential to shift these migration timings.