Iain A Malcolm
@iainamalcolm.bsky.social
Hydrologist, fisheries scientist, mountain biker, hiker. Science lead at SG Marine Directorate. Hon. Prof. at University of Aberdeen. Instream hydroecology, salmonids, fish assessment, river temperature, water quality. Personal Account. All views my own.
7. Logger calibration & QC are critical for the reliable assessment of river temperature trends. Failure to calibrate loggers can lead to spatio-temporal biases. These principles were core to the establishment of the Scotland River Temperature Monitoring Network #SRTMN www.gov.scot/publications...
July 19, 2025 at 4:34 PM
7. Logger calibration & QC are critical for the reliable assessment of river temperature trends. Failure to calibrate loggers can lead to spatio-temporal biases. These principles were core to the establishment of the Scotland River Temperature Monitoring Network #SRTMN www.gov.scot/publications...
6. In the Girnock Burn, loggers deployed before March 1998 were positively biased while those deployed ca. 1998 to 2007 were negatively biased. The combined effect of these two biases is to moderate the observed temperature trends over the period ca. 1988–2010 relative to the true trend.
July 19, 2025 at 4:34 PM
6. In the Girnock Burn, loggers deployed before March 1998 were positively biased while those deployed ca. 1998 to 2007 were negatively biased. The combined effect of these two biases is to moderate the observed temperature trends over the period ca. 1988–2010 relative to the true trend.
5. Using the bias corrected time-series it was shown that winter temperatures (December–February) were largely stable. Temperatures in other months increased non-linearly. Increases were greatest in summer (June–August) & for daily maximum temperatures, followed by daily mean and minimum.
July 19, 2025 at 4:34 PM
5. Using the bias corrected time-series it was shown that winter temperatures (December–February) were largely stable. Temperatures in other months increased non-linearly. Increases were greatest in summer (June–August) & for daily maximum temperatures, followed by daily mean and minimum.
4. We analysed trends in daily mean, max & min river temperature in the #Girnock Burn, the longest continuous sub-daily river temperature dataset in Scotland. Seasonal-Trend decomposition using Loess was undertaken on 1. raw & 2. bias corrected time-series to assess consequences for reported trends.
July 19, 2025 at 4:34 PM
4. We analysed trends in daily mean, max & min river temperature in the #Girnock Burn, the longest continuous sub-daily river temperature dataset in Scotland. Seasonal-Trend decomposition using Loess was undertaken on 1. raw & 2. bias corrected time-series to assess consequences for reported trends.
3. There are few long-term sub-daily river temperature time-series. These are often comprised of multiple logger/sensor combinations. Technological developments have increased memory, sampling frequency, reporting resolution, and precision of data. However, these changes can also introduce biases
July 19, 2025 at 4:34 PM
3. There are few long-term sub-daily river temperature time-series. These are often comprised of multiple logger/sensor combinations. Technological developments have increased memory, sampling frequency, reporting resolution, and precision of data. However, these changes can also introduce biases
13. EF data can provide accurate, catch independent estimates of abundance in rivers, provided they are collected & analysed using appropriate methods. By sampling multiple sites, assessment is possible at any scale. When combined with data on pressures this underpins evidence based management.
June 13, 2025 at 12:06 PM
13. EF data can provide accurate, catch independent estimates of abundance in rivers, provided they are collected & analysed using appropriate methods. By sampling multiple sites, assessment is possible at any scale. When combined with data on pressures this underpins evidence based management.
12. NEPS surveys provide an opportunity to characterise environmental pressures at the time of survey, including water quality and introgression. This information can be used to understand the critical thresholds and effect sizes and target management.
June 13, 2025 at 12:06 PM
12. NEPS surveys provide an opportunity to characterise environmental pressures at the time of survey, including water quality and introgression. This information can be used to understand the critical thresholds and effect sizes and target management.
11. At low population densities, assessment becomes more challenging as the proportion of sites where fish are present decreases & relative inter-site variability in density increases. Occupancy provides another potential metric of population health if a suitable benchmark could be produced.
June 13, 2025 at 12:06 PM
11. At low population densities, assessment becomes more challenging as the proportion of sites where fish are present decreases & relative inter-site variability in density increases. Occupancy provides another potential metric of population health if a suitable benchmark could be produced.
10. At the national scale salmon fry densities varied among years with rod catch (proxy of adult abundance). This was less clear for salmon parr, due to the effects of covid lockdowns on rod catches in 2021. Trout fry densities exhibited signs of density dependence in relation to sea trout catches
June 13, 2025 at 12:06 PM
10. At the national scale salmon fry densities varied among years with rod catch (proxy of adult abundance). This was less clear for salmon parr, due to the effects of covid lockdowns on rod catches in 2021. Trout fry densities exhibited signs of density dependence in relation to sea trout catches
9. Where habitats are saturated with juveniles (NEPS Grade 1) densities would be expected to remain fairly constant over time, independent of adult numbers due to density dependent competition (see Spey below). This was explored for a small number of catchments with longer-term multi-pass EF data.
June 13, 2025 at 12:06 PM
9. Where habitats are saturated with juveniles (NEPS Grade 1) densities would be expected to remain fairly constant over time, independent of adult numbers due to density dependent competition (see Spey below). This was explored for a small number of catchments with longer-term multi-pass EF data.
8. At a national scale, Atlantic salmon densities increased with increasing Strahler river order (bigger rivers), while trout densities declined. In general, spatial patterns persisted between years shifting up or down depending on overall abundance.
June 13, 2025 at 12:06 PM
8. At a national scale, Atlantic salmon densities increased with increasing Strahler river order (bigger rivers), while trout densities declined. In general, spatial patterns persisted between years shifting up or down depending on overall abundance.
7. Within the overall pattern of poor performance there was substantial regional variability. Fish stocks were assigned a Grade of 1-3 (1 healthy, 3 unhealthy) depending on performance against benchmark & uncertainty in abundance. Separate assessments were undertaken for each species & age class.
June 13, 2025 at 12:06 PM
7. Within the overall pattern of poor performance there was substantial regional variability. Fish stocks were assigned a Grade of 1-3 (1 healthy, 3 unhealthy) depending on performance against benchmark & uncertainty in abundance. Separate assessments were undertaken for each species & age class.
6. At a national scale salmon fry (0 year old) & parr (>0 year old) juvenile densities were substantially & significantly below the benchmark indicating that available habitats are no longer fully occupied. Trout fry & parr densities were also below the benchmark, but not significantly for fry.
June 13, 2025 at 12:06 PM
6. At a national scale salmon fry (0 year old) & parr (>0 year old) juvenile densities were substantially & significantly below the benchmark indicating that available habitats are no longer fully occupied. Trout fry & parr densities were also below the benchmark, but not significantly for fry.
5. The NEPS 2023 report updates existing capture probability (P) models for Scotland, illustrating that P varies with species, lifestage, pass, organisation, habitat, day of the year & region. Importantly there are also long-term trends in P emphasising the need for continued multi-pass data.
June 13, 2025 at 12:06 PM
5. The NEPS 2023 report updates existing capture probability (P) models for Scotland, illustrating that P varies with species, lifestage, pass, organisation, habitat, day of the year & region. Importantly there are also long-term trends in P emphasising the need for continued multi-pass data.
4. NEPS consists of an ecosystem of spatial data, standardised sampling methods , statistical models (capture probability and expected densities) and a GRTS statistical survey. These are brought together to assess status & trends in Atlantic salmon and brown trout populations in Scotland's rivers.
June 13, 2025 at 12:06 PM
4. NEPS consists of an ecosystem of spatial data, standardised sampling methods , statistical models (capture probability and expected densities) and a GRTS statistical survey. These are brought together to assess status & trends in Atlantic salmon and brown trout populations in Scotland's rivers.
3. Electrofishing (EF) data are commonly collected & accurate sources of information on ecosystem health, status & trends in diadromous fish. When collected to consistent protocols, with an appropriate survey, these data can provide reliable assessments across scales from sites to whole countries.
June 13, 2025 at 12:06 PM
3. Electrofishing (EF) data are commonly collected & accurate sources of information on ecosystem health, status & trends in diadromous fish. When collected to consistent protocols, with an appropriate survey, these data can provide reliable assessments across scales from sites to whole countries.
2. Evidence based freshwater fisheries management requires a reliable understanding of the processes regulating fish populations, the status (health) of populations across a range of spatial scales, the environmental pressures acting on them and the efficacy of management actions.
June 13, 2025 at 12:06 PM
2. Evidence based freshwater fisheries management requires a reliable understanding of the processes regulating fish populations, the status (health) of populations across a range of spatial scales, the environmental pressures acting on them and the efficacy of management actions.
1. Are you interested in assessing the status of Atlantic #salmon and brown #trout populations using electrofishing data? If so then this 🧵 is likely to be of interest to you. The latest report from the National Electrofishing Programme for Scotland #NEPS was published this week bit.ly/4jNrXH6 🧪🌎
June 13, 2025 at 12:06 PM
1. Are you interested in assessing the status of Atlantic #salmon and brown #trout populations using electrofishing data? If so then this 🧵 is likely to be of interest to you. The latest report from the National Electrofishing Programme for Scotland #NEPS was published this week bit.ly/4jNrXH6 🧪🌎
Up above Loch Tummel. Time to go hunt for that pot of gold.
April 27, 2025 at 9:02 PM
Up above Loch Tummel. Time to go hunt for that pot of gold.
Islay, distillery tour by bike. Time well spent in good company
April 15, 2025 at 10:29 PM
Islay, distillery tour by bike. Time well spent in good company
Another day on the Northumberland coast😁
March 9, 2025 at 11:55 PM
Another day on the Northumberland coast😁
Unwinding on the Northumberland coast. Beach walks, dogs, beer, food. Is there a better tonic?
March 7, 2025 at 6:26 PM
Unwinding on the Northumberland coast. Beach walks, dogs, beer, food. Is there a better tonic?
Wild Atlantic #salmon populations are in decline across their native range. In Scotland, "spring" stocks are of particular concern. Understanding population processes & drivers of change can inform management action. Detailed long-term monitoring provides these insights tinyurl.com/Girnock-and-...
January 30, 2025 at 10:44 AM
Wild Atlantic #salmon populations are in decline across their native range. In Scotland, "spring" stocks are of particular concern. Understanding population processes & drivers of change can inform management action. Detailed long-term monitoring provides these insights tinyurl.com/Girnock-and-...
Today was far too good to be at work! Cracking day out with excellent company. Somewhat baltic! #Scotland #Meagaidh @naturescot.bsky.social
January 10, 2025 at 7:49 PM
Today was far too good to be at work! Cracking day out with excellent company. Somewhat baltic! #Scotland #Meagaidh @naturescot.bsky.social