Assessment Protocol

This indicator uses two different approaches for evaluating whether good status is achieved. The approach used depends on the data used for the evaluation. If certain criteria are met, then the baseline approach is used. If not, then the trend-based approach is used.

 

Baseline approach

Coastal fish datasets must meet certain criteria in order to be able to apply an evaluation of good status using the baseline approach:

  1. The time period used to determine the baseline should cover a minimum number of years that is twice the generation time of the species most influential in the indicator evaluation. This is to ensure that the influence of strong year classes are taken into account. For coastal fish, this is typically about ten years. In this evaluation, the time period used to determine the baseline period against which good status is evaluated spans the years 1998-2010.
  2. The dataset used to determine the baseline must not display a linear trend within itself (n≥10, p>0.1), as the baseline for evaluation should optimally reflect the community structure at stable conditions and not a development towards a change in the environmental status.
  3. Before evaluating good status, it should also be decided whether or not the baseline reflects good status. This can be done either by using data dating back earlier than the start of the period used to determine the baseline, using additional information, or by expert judgment. For example, if data from time periods preceding the period used for determining the baseline have much higher indicator values, the baseline might represent not good status  (in case of an indicator where higher values are indicative of a good environmental state) or good status (in case of an indicator where higher values are indicative of an undesirable state).

Once the baseline status has been defined, threshold values are defined as the value of the indicator at the Xth percentile of the median distribution of the dataset used for determining the baseline. The median distribution is computed by resampling (with replacement) from the dataset used to determine the baseline. In each repetition, the number of samples should equal the number of years in the assessment period. In order to improve precision, a smoothing parameter may be added in each repetition. The smoothing parameter is computed as the normal standard deviation of the re-sampled dataset divided by the number of years resampled. To evaluate whether the threshold value is achieved during the evaluation period, the median value of the indicators during the evaluation period is compared with the specific threshold value (see Thresholds figure 1 and decision tree in Assessment protocol figure 1):

  1. In situations where the baseline conditions represent good status, the median of the years in the assessment period should be above the 5th percentile of the median distribution of the dataset used to determine the baseline in order to reflect good status.
  2. In situations where the baseline conditions represent not good status, the median of the years in the assessment period should be above the 98th percentile of the median distribution of the dataset used to determine the baseline in order to reflect good status. 

Trend-based approach

If the requirements for defining quantitative baseline conditions are not met (e.g. short time series, or a linear development during the period used to determine baseline conditions), then a trend based evaluation should be used. Data should date back to the early/mid-2000s to be included in the evaluation, and data should be ln-transformed to enhance linearity.

In the trend based approach, good status is defined based on the direction of the trend of the indicator compared to the desired direction of the indicator over time (Thresholds and Status evaluation figure 2). When the first years of the time series assessed represent good status, the trend of the indicator over time should not be negative in order to represent good status. If the first years of the time series assessed represent not good status, the trend in the indicator should be positive in order to represent good status. The level of significance for these trends should be p < 0.1.

 

Decision tree for evaluation using coastal fish community structure

The assessment protocol is found in figure 1.

Key coastal fish species Assessment figure 1.png

Key coastal fish species Assessment figure 1b.png

Assessment protocol figure 1. Decision tree for evaluation using coastal fish community structure. The baseline approach (top figure) and trendbased approach (bottom figure) are presented.

 

Assessment units

Due to the local appearance of typical coastal fish populations, status evaluations of coastal fish communities are representative for rather small geographical scales. In this evaluation the HELCOM assessment unit scale 3 'Open sub-basin and coastal waters' has been applied. The indicator is not evaluated for the open sea sub-basins since the species in focus are coastal.

Evaluations were carried out for 21 of the 42 assessment units and data up to 2016 was available for all but one assessment unit. The number of units evaluated is currently restricted by the availability of monitoring programs. 

In assessment units with several monitoring locations and data sets, the summed status (representing the majority of monitoring locations within the unit) is used to determine the status of the assessment unit. If equal numbers of monitoring locations/data sets have good status and not good status, then the one-out-all-out procedure is applied.

The assessment units are defined in the HELCOM Monitoring and Assessment Strategy Annex 4.

 

Data analyses

The data used for the evaluations are derived from fishery independent monitoring, recreational catch registration and/or commercial catch statistics.

Fishery independent monitoring

The analyses are based on catch per unit effort (CPUE) data from annual averages of all sampling stations in each area. To only include species and size-groups suited for quantitative sampling by the method, individuals smaller than 12 cm (Nordic Coastal multimesh nets) or 14 cm (other net types) were excluded from the assessment. Abundance is calculated as the number of individuals of the species included in the indicator per unit effort (CPUE).

Commercial catch data

Analyses were based on catch per unit effort data (CPUE) in the form of kg/gillnet day, and each data point represents total annual CPUE per area. The gillnets used have mesh sizes between 36-60 mm (bar length) and hence target a somewhat different aspect of the fish community in the area. In addition, fishing is not performed at fixed stations nor with a constant effort across years. As a result, the estimates from the gillnet monitoring programmes and commercial catch data are not directly comparable, and only relative changes across data sources should be compared.

Recreational catch registration

As for the other surveys, analyses were based on CPUE data (number of fish per effort) from monofilament gill nets or fyke nets. Voluntary recreational fishermen undertake fishing during the period April to November. For comparability only data from August was used in the current assessment. The fishermen fish at fixed stations and during the first half of each month throughout the season. This mediates the comparability of the data with fisheries independent monitoring programs using gill nets or fyke nets.