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q-bio.PE · Populations and Evolutionstat.AP · Applications

The fish community temperature index did not increase at 2,006 English river sites in 2000–2025 while air temperature rose 0.29 °C per decade; it followed summer temperature only from year to year

Question: Air temperature in England increased in 2000–2025. Did river fish communities change toward species from warmer climates? Data: We used 37,654 whole-community electric-fishing surveys of the Environment Agency (open data). The main panel has 2,006 fixed sites in 140 catchments, with at least 5 survey years over at least 10 years. Method: For 34 fish taxa, the species temperature index (STI) is the mean 1961–1990 air temperature (CRU TS 4.10) of the European 0.5° cells with GBIF records. The community temperature index (CTI) is the mean STI of the species present, or a weighted mean with log abundance. We calculated within-site trends with a catchment bootstrap, a species-shuffle null, a space-for-time benchmark, and a year-permutation test of year-to-year change. Results: The incidence CTI changed by −0.017 °C per decade (95% CI −0.028 to −0.007) and the abundance CTI by −0.021 (−0.039 to −0.003). At the same sites, air temperature increased by 0.29 °C per decade. Between sites, the CTI increases by 0.19 °C per °C, so the space-for-time expectation is +0.054 °C per decade. In 15 specifications (STI variants, survey method, season, site sets, 1990–2025, species removed), every upper 95% limit was +0.021 or less. Eel decline (−4.4 occupancy points per decade, warm STI) causes the negative sign; without eel the trend was +0.008 (−0.003 to +0.019). Species trends did not follow STI (rank correlation −0.15, 22 taxa), and observed trends were inside the species-shuffle null. Sites that warmed more did not change more. From year to year, the CTI increased by 0.015 °C per °C of same-year summer temperature anomaly (p = 0.011), but this sensitivity predicts only +0.004 °C per decade. Limitations: We used gridded air temperature, not water temperature. The STI comes from unevenly sampled GBIF records. Monitoring effort and recording of small species changed with time. The design is observational, and we did not test flow, barriers, stocking or water quality.

community temperature index · thermophilization · freshwater fish · river · England · Environment Agency · climate warming · species temperature index · GBIF · CRU TS · European eel · space-for-time · electric fishing

Admitted 5 citing publications

References

8
  1. doi:10.1073/pnas.2011639118

    Global riverine fish synthesis that found thermophilization; we test the same expectation in the English national survey network.

  2. supportsdoi:10.1016/j.watres.2025.123163

    Nunn et al. found increasing fish richness in English rivers; our panel shows richness +0.13 species per decade but no thermal shift.

  3. supportsAt 867 English river sites, fish communities changed by about one third of the amount that the between-site relation to invertebrate ASPT predicts (1990–2004 to 2012–2025) sci:sha256:0049ed3a20117b588f8b69d1066863b4683edc5ea8d25ee1f6ad7ad483ed87fd

    Same EA fish data; it found wide increases of bullhead, minnow, stone loach and stickleback and did not test temperature. Our species trends agree, and we add the temperature test.

  4. supportsYear-to-year biomass responses of demersal fish to bottom temperature were about 3% of their spatial temperature slopes in 13 trawl survey units (1963–2023) sci:sha256:73ec8e55114714e88c3a1d65b19dc7fbadba02fb93318f40a435610325a52c6a

    It found year-to-year fish responses far smaller than spatial temperature slopes; our year-to-year CTI sensitivity is about 8% of the spatial slope.

  5. supportsUK butterfly transect communities did not shift to warm-niche species at the rate of 1976–2024 site warming, while thermal niche predicted year-to-year responses sci:sha256:a37a9927e8c25069416d317953a1c1943c4017f40a065b89c7de4187728e5393

    UK butterfly CTI did not follow long-term warming while thermal niche predicted year-to-year responses; we find the same pattern in river fish.

  6. In 1990–2025 English river monitoring, smaller gains at equal starting status cause most of the slowdown in invertebrate pollution-sensitivity recovery sci:sha256:5c20e5dd85bd18c350f5a3a6a5c207b858888c49229f6f51b56657e8d32af6df

    Invertebrate pollution-sensitivity recovery in the same EA river network; background for non-thermal drivers of fish change.

  7. doi:10.1038/nclimate1347

    CTI and climatic debt method.

  8. usesdoi:10.1038/s41597-020-0453-3

    CRU TS v4 monthly temperature (version 4.10) for STI and site temperature.

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