Overview

The 2022 assessment of CSEMP contaminant and biological effects data includes an assessment of the status and trends of the fish disease index (FDI) in dab at monitoring stations around the UK. Assessments are made for a large number of time series, each of the fish disease index in dab at a single monitoring station. This document synthesises the results of the individual time series to assess the status and trends of the fish disease index at the biogeographic regional level.

The regional assessment only considers coastal and offshore stations and excludes estuarine stations. The results are therefore based on the monitoring data collected within the waters assessed under the UK Marine Strategy (MS). For simplicity, the term ‘region’ is used throughout to describe biogeographic regions. MS sub-regions are always referred to as such.

The following sections:


Summary of individual time series results

A time series of FDI fish disease indexs is assessed for status if:

  • there is at least one year with data in the period 2016 to 2021
  • there are at least three years of data over the whole time series
  • a parametric model can be fitted to the data and used to estimate the mean concentration in the final monitoring year (or, occasionally, if a non-parametric test of status is applied)

The conditions are more stringent for trends. Specifically, a time series is assessed for trends if:

  • there is at least one year with data in the period 2016 to 2021
  • there are at least five years of data over the whole time series
  • a parametric model can be fitted to the data and used to estimate the trend in mean fish disease index

Note that all trend assessments for individual time series and most status assessments are based on the fit of a parametric model. This is important because only the parametric results are passed into the regional assessments in the following sections. As it turns out, none of the FDI time series were assessed for status using a non-parametric test.

The first tab below shows all the monitoring stations where there are individual time series assessments of trend or status for FDI. The purple circles are stations where there is a trend assessment and the light blue cirles are stations where there is only a status assessment, The areas delineated by the thinner black lines are the biogeographic regions; those delineated by the thicker black lines are the MS sub-regions.

The next set of tabs show the trend and status assessments for FDI. The colours have the following meaning:

  • blue: the mean fish disease index is significantly (p < 0.05) below the Background Assessment Concentration (BAC)
  • green: the mean fish disease index is significantly (p < 0.05) below the Environmental Assessment Criterion (EAC)
  • red: the mean fish disease index is not signficantly below the EAC

And the shapes have the following meaning:

  • downward triangle: the mean fish disease index is significantly decreasing (p < 0.05)
  • circle: there is no significant change in mean fish disease index (p > 0.05) or there are too few years to test for trends
  • upward triangle: the mean fish disease index is significantly increasing (p < 0.05)

The final set of tabs give:

  • the number of time series with upwards, downwards or no trend in each biogeographic region and MS sub-region
  • the same information presented as proportions
  • the number of time series with blue, green or red status in each biogeographic region and MS sub-region
  • the same information presented as proportions


Stations


#### FDI


Trend summary (numbers)

Number of time series with upwards, downwards or no trend by biogeographic region and MS sub-region

MS sub-region biogeographic region status FDI
Greater North Sea Northern North Sea upward trend 3
no trend 5
downward trend 0
Southern North Sea upward trend 0
no trend 6
downward trend 0
E Channel upward trend 0
no trend 2
downward trend 0
total upward trend 3
no trend 13
downward trend 0
Celtic Seas Minches & W Scotland upward trend 1
no trend 0
downward trend 0
Irish Sea upward trend 1
no trend 5
downward trend 0
W Channel & Celtic Sea upward trend 0
no trend 1
downward trend 1
total upward trend 2
no trend 6
downward trend 1


Trend summary (proportions)

Proportion of time series with upwards, downwards or no trend by biogeographic region and MS sub-region

MS sub-region biogeographic region status FDI
Greater North Sea Northern North Sea upward trend 38
no trend 62
downward trend 0
Southern North Sea upward trend 0
no trend 100
downward trend 0
E Channel upward trend 0
no trend 100
downward trend 0
total upward trend 19
no trend 81
downward trend 0
Celtic Seas Minches & W Scotland upward trend 100
no trend 0
downward trend 0
Irish Sea upward trend 17
no trend 83
downward trend 0
W Channel & Celtic Sea upward trend 0
no trend 50
downward trend 50
total upward trend 22
no trend 67
downward trend 11


Status summary (numbers)

Number of time series with each status by biogeographic region and MS sub-region

MS sub-region biogeographic region status FDI
Greater North Sea Northern North Sea blue 0
green 6
red 5
Southern North Sea blue 0
green 7
red 1
E Channel blue 0
green 2
red 0
total blue 0
green 15
red 6
Celtic Seas Minches & W Scotland blue 0
green 1
red 0
Irish Sea blue 0
green 10
red 0
W Channel & Celtic Sea blue 1
green 2
red 0
total blue 1
green 13
red 0


Status summary (proportions)

Proportion of time series with each status by biogeographic region and MS sub-region

MS sub-region biogeographic region status FDI
Greater North Sea Northern North Sea blue 0
green 55
red 45
Southern North Sea blue 0
green 88
red 12
E Channel blue 0
green 100
red 0
total blue 0
green 71
red 29
Celtic Seas Minches & W Scotland blue 0
green 100
red 0
Irish Sea blue 0
green 100
red 0
W Channel & Celtic Sea blue 33
green 67
red 0
total blue 7
green 93
red 0


Regional assessment - methods

Tabulating the number of time series with each status category by region provides a quick summary of the individual time series results. However, it does not provide an objective regional assessment of status. Similarly, tabulating the number of time series with an upward or downward trend does not provide an objective regional assessment of trend. This section describes how the individual time series results can by synthesised in a meta-analysis to assess both status and trend at the regional level.

Status

For a regional status assessment, the status of each time series is summarised by the estimated mean fish disease index in the final monitoring year. This is sufficient because the BAC and EAC do not vary between time series. Regional status is then estimated by fitting the following linear mixed model by restricted maximum likelihood:

  • response: status (mean fish disease index)
  • fixed model: region
  • random model: status estimation variation + residual variation

where status estimation variation is the variation in the status estimates from the individual time series analysis, assumed known and fixed.

There are no restrictions on the time series used in the status meta-analysis based on the classification of the monitoring station; time series from baseline, representative and impacted stations are all included.

Again, the meta-analysis is restricted to regions with at least three status stations with good geographic spread.


Regional assessment - availability of time series

This section provides more detail on the number and geographic spread of the time series available for the meta-analyses. The map shows the stations with parametric trend and status assessments, having excluded trend assessments at impacted stations. The purple circles are stations where there is a trend assessment and the light blue cirles are stations where there is only a status assessment,

The following regions have an insufficient number or time series or spread of stations and are excluded from the regional assessment:

  • trend: E Channel, Minches & W Scotland, W Channel & Celtic Sea
  • status: E Channel, Minches & W Scotland



Regional status

The first 2 tabs show:

  • Regional status: estimates of the regional status for FDI with pointwise upper one-sided 95% confidence intervals; the grey vertical lines are the BAC and the EAC
  • Individual time series: the status estimates from the individual time series on which the regional assessment is based. The estimates for regions with insufficient geographic spread (and excluded from the meta-analysis) are also shown.

The symbols in all the plots have the following interpretation:

  • blue: the mean fish disease index is significantly (p < 0.05) below the Background Assessment Concentration (BAC)
  • green: the mean fish disease index is significantly (p < 0.05) below the Environmental Assessment Criterion (EAC)
  • red: the mean fish disease index is not significantly below the EAC

The final tab shows the estimates of the regional status in FDI.


Regional status


Individual time series


Estimates by region

This table shows the estimates of the regional status:

  • status: the estimated mean fish disease index
  • se: the corresponding standard error
  • upper: the corresponding pointwise upper one-sided 95% confidence limit


biogeographic region status se upper BAC EAC
Northern North Sea 4.43 0.56 5.36 1.51 6.72
Southern North Sea 4.13 0.62 5.15 1.51 6.72
Irish Sea 3.40 0.57 4.34 1.51 6.72
W Channel & Celtic Sea 0.73 0.99 2.36 1.51 6.72