Use constraints: Data can be used freely given that the source is cited (following creative commons license CC-BY). The source should be cited as: “HELCOM HOLAS 3 Dataset (2023).

For ICES rectangles surveyed by BIAS, the values shown are the mean values per ICES rectangle based on BIAS data, average for 2016-2020. For ICES rectangles not surveyed by BIAS, values are calculated as:

MAX-value x Weighting factor. The weighting factor is specific to each ICES rectangle, calculated as the ratio between the commercial landings in that rectangle and the commercial landings in the ICES rectangle with the highest landings (based on averages for 2011-2016). MAX-value = millions of herring according to BIAS in the ICES rectangle with the highest landings.

ICES rectangles outside the BIAS survey area with no reported fish landings were given the value 0.

The relative abundance values in each ICES rectangle were divided by the area of the rectangle to obtain values per 1 km2. If the values in small coastal ICES rectangles (outside BIAS area) became unrealistically large due to high herring landings, the value of the neighboring rectangle was given. The final layer was converted to 1 km x 1km grid cells.

Data source:

Baltic International acoustic survey (BIAS) data from 2016-2020, from ICES WGBIFS reports

- Does not cover the whole Baltic Sea.

- Reported as millions of fish / ICES statistical rectangle

- all ages included

Landings data from EU Joint Research Centre ( https://datacollection.jrc.ec.europa.eu/dd/effort/maps) from years 2016-2020 (= fisheries data).

- Data reported as tonnes / ICES statistical rectangle

Data quality:

The quality of fisheries independent BIAS data can be considered good, as the surveys are specifically designed for estimating fish abundance in the Baltic Sea. Outside BIAS area, the quality of the data decreases, as it is based on an estimate based on weighting derived from landings data.

Attribute information: Ecosystem abundance value from 0 to 1 (millions of fish / km2, log-transformed and normalized)