Human impacts on global freshwater fish biodiversity

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Science  19 Feb 2021:
Vol. 371, Issue 6531, pp. 835-838
DOI: 10.1126/science.abd3369

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No waters left untouched

We are increasingly aware of human impacts on biodiversity across our planet, especially in terrestrial and marine systems. We know less about fresh waters, including large rivers. Su et al. looked across such systems globally, focusing on several key measures of fish biodiversity. They found that half of all river systems have been heavily affected by human activities, with only very large tropical river basins receiving the lowest levels of change. Fragmentation and non-native species have also led to the homogenization of rivers, with many now containing similar species and fewer specialized lineages.

Science, this issue p. 835


Freshwater fish represent one-fourth of the world’s vertebrates and provide irreplaceable goods and services but are increasingly affected by human activities. A new index, Cumulative Change in Biodiversity Facets, revealed marked changes in biodiversity in >50% of the world’s rivers covering >40% of the world’s continental surface and >37% of the world’s river length, whereas <14% of the world’s surface and river length remain least impacted. Present-day rivers are more similar to each other and have more fish species with more diverse morphologies and longer evolutionary legacies. In temperate rivers, where the impact has been greatest, biodiversity changes were primarily due to river fragmentation and introduction of non-native species.

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