Interim report of the HELCOM CORESET project

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2.5. Abundance of wintering populations of seabirds
1. Working team: Sea birds
Authors: Henrik Skov, Martin Green, Susanne Ranft, Martti Hario
2. Name of core indicator
Abundance of wintering populations of seabirds
3. Unit of the core indicator
A summary index, based on population sizes of
selected seabird species
4. Description of proposed indicator
Seabirds are important predators in the marine ecosystem. In the wintertime, seabirds aggregate in certain
feeding grounds where their abundances can be monitored. The indicator follows the abundance of seabirds
in the winter. It follows the birds on three levels: species, functional groups and total abundance.
Integration at the group level: Species have been assigned to functional groups where the species abundances
are weighted based on population size of respective species.
Integration of the all species regardless of their functional groups describes the total abundance of wintering
seabirds in an area.
With repeated collection of data trends can be calculated over time.
5. Functional group or habitat type
Coastal pelagic fi sh feeder, offshore pelagic fi sh feeder, Subtidal offshore benthic feeder, Subtidal coastal
benthic feeder, Subtidal herbivorous benthic feeder
6. Policy relevance
Descriptor 1, criterion 1.2 Population size
Descriptor 4, criterion 4.2 Abundance/distribution of key trophic groups and species
(Descriptors 5 & 6: indirectly)
7. Use of the indicator in previous assessments
None
8. Link to anthropogenic pressures
The seabird abundance in the winter is directly impacted by oil spills, by-catch, hunting, displacement by
offshore constructions and shipping traffi c.
It is indirectly impacted by eutrophication and physical disturbance of bottom sediments (through
changes in food supplies).
9. Pressure(s) that the indicator refl ect
Selective extraction of species, introduction of synthetic compounds (oil spills), input of fertilisers and
organic matter, abrasion and selective extraction, changes in siltation and thermal regime, other physical
disturbance.
10. Spatial considerations
Winter concentrations of key species do not occur abundantly in the northern part of the Baltic but are
confi ned to areas in the Baltic proper and southwards.
11. Temporal considerations
Monitoring frequency: ideally as often as possible, but at maximum circa every fi fth year.
12. Current monitoring
Part of international waterfowl monitoring in several member states. Some kind of annual data collection
(mainly coastal) is currently being made. Offshore monitoring is being conducted with longer intervals
but plans for more regular monitoring (every 3-5 years) exist in at least some member states.
13. Proposed or perceived target setting approach with a short justifi cation.
The GES is tentatively defi ned as a 50% deviation from mean of the reference period of 1992-1993.
Introduction
Water birds are an important part of the marine ecosystem, being predators of fi sh and benthic fauna and
herbivores in coastal areas. Their abundance is supported by the ecosystem productivity, but they also
have top-down impacts on their prey species. In the Baltic Sea, majority of waterbird species overwinter in
the marine area, aggregating in suitable feeding habitats. Hence, the abundance wintering and breeding
populations respond to different pressures and they should be assessed separately.