Interim report of the HELCOM CORESET project

with one net for one night. A minimum of 10 stations are fi shed in each depth interval down to 10 meters
depth, and a minimum of 5 stations in the deepest depth interval. The method is currently used only in
Finland and Sweden, where it is routinely used in all areas established after 2001.
Monitoring by all methods is performed at fi xed stations. The gears are set between 14.00 and 16.00 and
lifted the next day between 07.00 and 10.00. Catches at each station are registered as numbers per species
and length group (2,5 or 1 cm), separately for each mesh size (or net). Additionally, wind strength and
direction, water temperature, and water transparency measured using a Secchi disc, are routinely monitored
during the fi shing period.
Additional data sources such as commercial catch statistics based on EU-data collection system, coastal
echo sounding, etc. might serve as a complement if the data proves to be of enough quality to assess the
biodiversity of coastal fi sh communities.
Methodology of data analyses
Index computation
Species Abundance Index. The indicator is estimated as the catch per unit effort of the key species (i.e.
Perch) within the target size range of the gear used.
Species Demographic Index. The indicator is estimated as the mean length of all individuals of the key species
(i.e. Perch) within the target size range of the gear used and/or the catch per unit effort of all Perca
fl uviatilis equal to or above 20 cm length.
Community Diversity Index. The indicator is the Shannon index calculated based on catch per unit effort of
all species targeted by the gear used and within its target size range.
Community Size Index. The indicator is the catch per unit effort of individuals equal to or larger than 30
(Net series) or 40 (Coastal survey nets and Nordic coastal multi-mesh nets) cm of all species targeted by the
gear used, within its target size range.
Community Abundance Index. The index includes measures of catch per unit effort of the groups of Cyprinids
and Piscivores, respectively. The group Cyprinids includes all species within the Cyprinidae, and the
group piscivores includes all species with a trophic level equal to or higher than 4.0 according to Fish Base
(www.fi shbase.org).
Community Trophic Index. The index represents the mean trophic level of the community and is based
on catch per unit effort of all species targeted by the gear used, within its target size range. The trophic
level of each species is based on values from Fish Base (www.fi shbase.org), and the index is calculated as
� (Trophic level x Relative Abundance) species i. As a complement, the proportion of piscivores is used,
defi ning piscivores as species with a mean trophic equal to or above 4, according to Fish Base.
Target species and size range
In order 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 (Net series, Coastal survey nets), and all
small-bodied species (gobies, sticklebacks, butterfi sh), and species with eel-like body forms (taeniform,
anguilliform or fi liform shapes) are excluded (HELCOM 2011).
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