B7: Health of freshwaters assessed through fish populations
Short Description
This indicator tracks changes in populations of native freshwater fish in England. Fish are a good indicator of healthy freshwater environments, responding to changes in water quality (including temperature) and quantity, as well as the quality of river habitats, necessary to sustain healthy populations and enable migration throughout rivers to allow fish to complete their life cycles. Fish also provide an important recreational and economic benefit from freshwaters.
Readiness and links to data
This indicator is not available for reporting in 2024 in a finalised form. An interim indicator is presented here that shows (a) the proportion of principal salmon rivers at risk in England and, additionally, (b) the classification of fish species within English rivers.
B7a presents annually published national salmon stock data. For this assessment, each river’s salmon stocks are placed into one of 4 categories: at risk; probably at risk; probably not at risk; and not at risk. These categories reflect the level of resilience of salmon stocks in each river in relation to biological reference points.
B7b reflects the ecological status of whole fish communities in rivers and is based on outputs from the Fish Classification System (FCS2). The results show whether the fish community in a particular river reflects high; good; moderate; poor or bad ecological conditions. These data also contribute to the assessment of ecological status in rivers (B3a). Further work may examine the geographical coverage of the indicator..
Indicator components
Figure B7a: Salmon stock status – principal salmon rivers in England within each risk category, 2006 to 2022
Table B7a: Salmon stock status – principal salmon rivers in England within each risk category, 2006 to 2022
| Year | At risk | Not at risk | Probably at risk | Probably not at risk |
|---|---|---|---|---|
| 2006 | 38.10 | 21.43 | 21.43 | 19.05 |
| 2007 | 40.48 | 21.43 | 16.67 | 21.43 |
| 2008 | 35.71 | 23.81 | 7.14 | 33.33 |
| 2009 | 30.95 | 14.29 | 23.81 | 30.95 |
| 2010 | 33.33 | 26.19 | 19.05 | 21.43 |
| 2011 | 23.81 | 23.81 | 28.57 | 23.81 |
| 2012 | 26.19 | 16.67 | 28.57 | 28.57 |
| 2013 | 38.10 | 14.29 | 30.95 | 16.67 |
| 2014 | 23.81 | 0.00 | 66.67 | 9.52 |
| 2015 | 28.57 | 0.00 | 52.38 | 19.05 |
| 2016 | 33.33 | 0.00 | 57.14 | 9.52 |
| 2017 | 21.43 | 0.00 | 64.29 | 14.29 |
| 2018 | 28.57 | 0.00 | 61.90 | 9.52 |
| 2019 | 57.00 | 0.00 | 36.00 | 7.00 |
| 2020 | 48.00 | 2.00 | 40.00 | 10.00 |
| 2021 | 74.00 | 2.00 | 14.00 | 10.00 |
| 2022 | 71.43 | 2.38 | 14.29 | 11.90 |
Trend description for B7a
Across the most recent two datapoints (2021 to 2022) there has been a small improvement, with a 2.5% decrease in the percentage of rivers 'at risk' and a 2% increase in the percentage of rivers 'probably not at risk'. However, the overall status of salmon stocks across principal salmon rivers continues to show a decline over the total period of this assessment. This continues a trend observed before the start of the time series (2006). The percentage of principal salmon rivers at risk in England has fluctuated considerably from year to year; but has shown a significant increase over the past 5 years (43%), this includes a 26% increase between 2020 and 2021. The percentage of rivers in the ‘probably at risk’ category has decreased over the same 5 year time period by 48%, (from 62% in 2018 to 14% in 2022). In comparison, the percentage of rivers in the ‘not at risk’ category fell from 21% in 2006 to 0% in 2014 where it remained until there was a slight (2 percent) recovery in 2020 and maintained at this level through 2022. The percentage of rivers that are ‘probably not at risk’ has fallen by 7% over the 16 years covered by this indicator.
Assessment of change
An increase (or improvement) in the numbers of the principal salmon rivers classed as ‘Not at risk’ or ‘Probably not at risk’ was observed over the short term, while a decrease (or deterioration) was observed over the medium and long term. This indicator is derived from highly variable data as fish are susceptible to yearly weather patterns and have natural cycles in abundance. This reduces confidence that shorter-term assessment results reflect real trends rather than natural variation. A more marked deterioration is evident over the medium term, reflecting a steep drop after 2012.
Change since 2018 has also been assessed. Since 2018, there has been an increase (or improvement) for the indicator for principal salmon rivers classed as ‘Not at risk’ or ‘Probably not at risk’. However, this improvement is slight and as stated above is dependent on data with a high yearly variation. Moreover, the result is based on only 5 data points so should be considered as indicative and not evidence of a clear trend.
Further information on this assessment, along with details on the methodology, is provided in the Assessment background. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results.
Table B7a: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| B7a | Not at risk or probably not at risk | Short term | 2016 to 2021 | 6.63 | Loess | Improvement |
| B7a | Not at risk or probably not at risk | Medium term | 2011 to 2021 | -73.08 | Loess | Deterioration |
| B7a | Not at risk or probably not at risk | Long term | 2006 to 2021 | -70.15 | Loess | Deterioration |
Note that assessment categories for the short, medium and long term were assigned based on smoothed data, so percent change figures in Tables B7a may differ from unsmoothed values quoted elsewhere. Percent change refers to the difference seen from the first to last year in the specified date range.
Figure B7b: Classification of fish in English rivers, 2009 to 2022
Table B7b: Classification of fish in English rivers, 2009 to 2022
| Year | Bad | Good | High | Moderate | Poor |
|---|---|---|---|---|---|
| 2009 | 1.48 | 32.55 | 9.23 | 32.36 | 24.39 |
| 2010 | 2.00 | 32.92 | 10.91 | 31.14 | 23.03 |
| 2011 | 1.33 | 35.51 | 12.91 | 28.89 | 21.35 |
| 2012 | 1.34 | 35.70 | 13.84 | 28.48 | 20.64 |
| 2013 | 0.69 | 36.38 | 12.07 | 30.81 | 20.04 |
| 2014 | 0.72 | 36.53 | 11.92 | 32.07 | 18.76 |
| 2015 C1 | 0.70 | 35.27 | 12.78 | 32.77 | 18.47 |
| 2015 C2 | 6.51 | 27.55 | 14.43 | 26.79 | 24.73 |
| 2016 | 6.44 | 26.66 | 14.77 | 27.45 | 24.67 |
| 2019 | 6.57 | 26.49 | 15.14 | 27.64 | 24.15 |
| 2022 | 6.00 | 27.00 | 16.00 | 27.00 | 24.00 |
Trend description for B7b
The data show a slight but consistent increase in the numbers of rivers classed as high and good ecological status for fish between 2009 and 2015 and a corresponding small decrease in numbers of rivers in the poor and bad categories. From 2015, a revised method for assessing status was introduced, indications are that there was little change in the proportions of rivers in the 5 different categories between 2016 and 2022, overall there has been a 1% increase in the percentage of rivers at 'good' or 'high' status. The new method is not directly comparable to the old method, so it is not appropriate to assess trend across both datasets at this time.
Assessment of change
Change since 2018 has not been assessed for this indicator as sufficient data are not yet available. An increase (or improvement) has been observed for the percent of English rivers classified as in high or good status based on fish, over the short term, covering the period of time between 2009 and 2014. From 2015, a new method was introduced for assessing status and there are not yet sufficient data points to assess a trend. The new method is not directly comparable to the old method, so it is not appropriate to look at trends across both datasets. When a suitable time series is built up with the new method, this more recent data will be assessed. There is not a sufficiently long time series for making an assessment over the medium and long-term periods.
Further information on this assessment, along with details on the methodology, is provided in the Assessment background. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results.
Table B7b: Assessment of change
| Component | Subcomponent | Period | Date range | Percentage change | Smoothing function | Assessment of change |
|---|---|---|---|---|---|---|
| B7b | High or good | Short term | 2009 to 2014 | 16.11 | Loess | Improvement |
| B7b | High or good | Medium term | N/A | N/A | N/A | Not assessed |
| B7b | High or good | Long term | N/A | N/A | N/A | Not assessed |
Note that assessment categories for the short, medium and long term were assigned based on smoothed data, so percentage change figures in Tables B7b may differ from unsmoothed values quoted elsewhere. Percentage change refers to the difference seen from the first to last year in the specified date range.