This core indicator evaluates the status of coastal sea areas of the Baltic Sea based on the abundance of sea trout parr in rivers where they breed. The determination of whether good status is reached is based on a comparison of the observed parr densities in rearing habitats with the reference potential parr densities in the specified habitats. The current evaluation assesses the status of sea trout populations using data from 2011-2016 and expert evaluations.
Key message figure 1. Status assessment results based evaluation of the indicator 'abundance of sea trout spawners and parr'. The assessment is carried out using Scale 3 HELCOM assessment units (defined in the HELCOM Monitoring and Assessment Strategy Annex 4). Click here to access interactive maps at the HELCOM Map and Data Service: Abundance of seatrout spawners and parr.
The current evaluation shows that the status reflected by populations of sea trout is not good in most of Northern Baltic Sea coastal areas. Threshold values are not achieved in the Bothnian Bay, the Bothnian Sea and Northern Gulf of Finland. A positive development in parr densities since 2012 has been observed in some rivers in Finland (Gulf of Finland), and Sweden (Bothnian Sea), reflecting management improvements in these countries.
In the Southern Gulf of Finland and Baltic Proper, the status of sea trout stocks is better in eastern and south-western sub-basins where the majority of stocks reach production levels reflecting good status.
The level of confidence of the assessment is moderate to high.
The indicator is applicable in the rivers of all countries bordering the Baltic Sea.
The densities of parr measured in rearing areas in rivers reflect the abundance of the adult sea trout spawners and success of recruitment. Adult sea trout carry out feeding migrations in the Baltic Sea where they are a top predatory fish.
Sea trout abundance is affected by commercial and recreational fishing at sea and in rivers. The parr densities measured in rivers are affected by migration barriers to reproduction areas and habitat quality. Thus the indicator reflects the state of the ecosystem as it is sensitive to river connectivity (e.g. effect of dams) and the quality of spawning and rearing habitats.
Biodiversity and nature conservation
D1C2 The The population abundance of the species is not adversely affected due to anthropogenic pressures, such that its long-term viability is ensured.
D1C3 The population demographic characteristics (e.g. body sizeor age structure, sex ratio, fecundity, and survival rates) of the species are indicative of a healthy population which is not adversely affected due to anthropogenic pressures.
Ecosystems, including food webs.
D3 Populatiojns of all commercially-exploited fish and shellfish are within safe biological limits, exhibiting a population age and size distribution that is indicative of a healthy stock.
HELCOM (2018) Abundance of sea trout spawners and parr. HELCOM core indicator report. Online. [Date Viewed], [Web link].
Abundance of sea trout spawners and parr HELCOM core indicator 2018 (pdf)