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.
Coastal fish datasets must meet certain criteria in order to be able to apply an evaluation of good status using the baseline approach:
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):
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.
The assessment protocol is found in figure 1.
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.
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.
The data used for the evaluations are derived from fishery independent monitoring, recreational catch registration and/or commercial catch statistics.
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).
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.
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.