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At English river sites in 1990–2025, brown trout density rose where nearby invertebrate pollution scores improved, but 18 other fish taxa and species richness showed no consistent link

Question: River invertebrate scores in England show recovery from organic pollution since 1990. Does fish abundance change at a site when the invertebrate score at the same place changes? A parallel SCI study (f124493a) tested fish presence; we test density with other designs. Approach: We used 42,837 Environment Agency electric-fishing surveys (May-October, 1990-2025). We matched fish sites to the nearest invertebrate site in the same WFD waterbody within 2 km. The predictor is RICT observed/expected WHPT ASPT (O/E). We used two designs: a within-site panel (14,516 surveys, 4,535 sites, site and region-year fixed effects) and a site long difference (first vs last 5-year block, median 1998-2016, region-year anomalies, catchment fixed effects, 767 sites). Results: Brown trout was the only one of 19 taxa with p < 0.01 in both designs. Per +0.1 O/E, log(1 + density) changed by +0.051 (95% CI 0.015 to 0.087) in the panel and +0.177 (0.057 to 0.296) in the long difference. Holm-adjusted p values for 19 taxa are 0.12 and 0.08. Atlantic salmon was positive only in the panel (+0.078, p = 0.03; long difference -0.001). The other 17 taxa (grayling, bullhead, minnow, lampreys, cyprinids, eel, pike, perch, stickleback) and species richness had no significant link in either design. The trout link peaked for same-year invertebrate samples, was absent for later invertebrate years, came mainly from the slow site trend, and was largest for invertebrate sites within 2 km in the same waterbody (0.16) and smaller at 2-20 km (0.04-0.06). The link is weak (r = 0.13). The O/E family-count index did not predict trout. A presence version gave trout and roach slopes close to f124493a. Without the anomaly step, calendar timing inflated the long-difference slope by 50-60%. Limitations: Data are observational. Shared local drivers (flow, habitat works, stocking, survey changes) can cause both signals. Electric-fishing catch is an uncalibrated index. Matching does not use river network distance. Conclusion: Invertebrate gains are a poor proxy for fish abundance recovery in English rivers; only brown trout shows a small, local coupling.

freshwater fish · macroinvertebrates · water quality · WHPT ASPT · RICT · brown trout · Atlantic salmon · National Fish Populations Database · Environment Agency · England · river recovery · electric fishing · fixed effects · long difference · biological indicators

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References

8
  1. usesIn 1990–2025 English river monitoring, smaller gains at equal starting status cause most of the slowdown in invertebrate pollution-sensitivity recovery sci:sha256:5c20e5dd85bd18c350f5a3a6a5c207b858888c49229f6f51b56657e8d32af6df

    We use the RICT O/E WHPT ASPT site-year tables and EA invertebrate site table that this study retained (SCI shared dataset sha256-75ce6f8f73713c141f2385e31659f3042d74980f55c3f5baffb8bc2678b5dee3).

  2. 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

    Independent site-matched test with the same EA sources. With density, other designs and a presence version, we also find a positive brown trout link, no long-term salmon link, no richness link, and a roach presence slope of the same size; roach density showed no significant link.

  3. supportsdoi:10.1016/j.watres.2025.123163

    National NFPD trends found no consistent increase in pollution-intolerant fish; our site-matched test agrees for all taxa except a small brown trout link.

  4. doi:10.1016/j.scitotenv.2023.163107

    Evidence of invertebrate recovery from gross pollution in English and Welsh rivers.

  5. doi:10.1016/j.scitotenv.2023.167144

    Invertebrate biodiversity improvement in English rivers over 30 years.

  6. doi:10.1111/j.1365-2486.2012.02662.x

    Long-term trends in British river macroinvertebrates.

  7. doi:10.1111/j.1365-2400.2007.00575.x

    European fish functional guild lists that informed our a priori tolerance groups.

  8. doi:10.1111/jfb.14119

    Electric-fishing catch calibration can bias abundance trends; a limitation of our catch index.

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