Exactly counted river fish decreased by similar amounts at cold and warmer English sites in 1993–2025, so the US cold-versus-warm stream divergence did not replicate
Question: Rumschlag et al. (2025) found that US river fish abundance (-53%) and richness (-32%) decreased in cold streams (summer water below 15.4 °C) in 1993-2019, with small change in intermediate streams. Does this occur in England? Data: Environment Agency fish survey data (13,012 electric-fishing surveys at 965 fixed sites in 111 catchments, 1993-2025, each site with 8 or more survey years) and EA spot measurements of July-August water temperature within 2 km of the sites (61,928 June-September records downloaded). Half of the sites are below 15.4 °C; no site is above the US warm limit. Method: Per-site quasi-Poisson trends of first-run density and Poisson trends of taxon richness; 27-year change with 2,000 catchment-bootstrap resamples; gradient of site trend on temperature; taxon occurrence models with site fixed effects; 23 sensitivity runs. Results: The pre-planned all-taxa density gave cold sites -29% (95% CI -44 to -11) and other sites +3% (-22 to +28). This result is not reliable: small benthic taxa are often recorded only as abundance classes, the class fraction changed with time, and without class records the cold-site change was -1% (-17 to +19). For the 19 taxa that are always counted exactly (salmonids and coarse fish), density decreased at cold sites (-33%, -40 to -24) and at other sites (-26%, -40 to -9), with no temperature gradient (+0.14% per year per °C, -0.17 to +0.43). This was true in all sensitivity runs. Richness did not decrease at cold sites (+0.4%, -4.7 to +6.4; other sites +7.0%). The community thermal index decreased slightly (-0.016 °C per decade). Warm-water coarse fish became less frequent at cold sites, and small cool-water taxa became more frequent everywhere. Conclusion: cold sites decreased, but intermediate sites decreased by a similar amount, so the US divergence did not replicate in England. Limitations: spot daytime temperatures, no warm-class sites, monitoring sites not a random sample, changes in gear and recording, observational design.
freshwater fish · river monitoring · water temperature · climate change · replication · abundance trends · species richness · England · Environment Agency · electric fishing · community temperature index · recording artefact
References
5- challengesdoi:10.1038/s41586-025-09556-0
We test its cold-versus-warm divergence of river fish abundance and richness with English data; the divergence did not replicate for exactly counted fish or richness.
- supportsFish at cold English river sites did not decline in 1993–2019 as in US cold streams; a larger richness gain at warm sites was mostly in one region with more small-species records sci:sha256:fd29ff96a369e1a2e5fc4544110a54685f88c19202a6afab319d0eb7f6fbdf52
Same question with air-temperature classes; we agree there is no US-like divergence or cold-site richness decrease, and we show that all-taxa density depends on abundance-class records and the estimator, while exactly counted taxa decreased at all temperatures.
- supportsThe 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 sci:sha256:550a7813860bff7d8da43b0ecd993fd3a56d8a89daeb2977a19ccf4a721aec1a
Our community thermal index from English water temperatures gives almost the same small decrease as its index from European air temperatures.
- doi:10.1016/j.watres.2025.123163
Earlier national analysis of the same fish database (richness trends since the 1980s).
- doi:10.1073/pnas.2011639118
Global evidence of thermophilization of riverine fish communities.
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