The Living Planet Index for Migratory Freshwater Fishes: 2024 update

Migratory fishes that spend all or parts of their life cycle in freshwater are highly threatened , and a previous analysis confirmed widespread catastrophic declines in their abundance. Here, we provide an update of these trends using an improved selection of species and data set extending further into the present. Based on abundance information from the Living Planet Database for 1,864 populations of 284 native migratory freshwater fish species, we find that globally, the index has declined by 81%. The majority (65%) of species have declined on average, while 31% have increased on average, with the majority of species trends being either very positive or very negative. Average declines have been more pronounced in Europe (−75%) and Latin America & Caribbean (−91%), and less in North America (−34%) and Asia-Oceania (−28%). The percentage of species represented was highest in the two temperate regions of Europe and North America, and Latin America & Caribbean (between 30 and 45%). Data was highly deficient for Asia-Oceania, and particularly Africa, for which no reliable trend could be produced. Populations that are known to be affected by local threats show an average decline of 96% while those not threatened at the population level have increased on average. Habitat degradation, alteration, and loss accounted for around a half of threats to migratory fish, while overexploitation accounted for just under one-third of recorded threats. Populations receiving management declined less than unmanaged ones, with most management activities relating to some form of fisheries management (42%; this included fishing restrictions, stocking, bycatch reductions, supplementary feeding and no-take zones), and this was most commonly cited in North America and Europe. Habitat management accounted for only 9% of recorded management activities, despite the prominence of habitat-related threats to populations in the data set. Recorded reasons for observed increases tended to be mostly unknown or undescribed, especially in tropical regions. Although both the species selection method and data set have been improved since the last report, data and knowledge gaps remain, and more quantitative data and analysis are needed to obtain a more detailed picture of how populations are changing and the different factors interacting and driving this change. We conclude with a list of recommendations for improving our understanding of the fate of migratory freshwater fishes and developing practical solutions that restore and protect them and the ecosystems upon which they depend.