Interim report of the HELCOM CORESET project

2.4. Productivity of white-tailed eagles
1. Working team: Sea birds
Authors: Björn Helander, Christof Herrmann and Anders Bignert
2. Name of core indicator
Productivity of white-tailed eagles
3. Unit of the core indicator
The mean number of nestlings of at least three
weeks of age, out of all occupied nests.
4. Description of proposed indicator
The productivity of white-tailed eagle in the coastal zone (15 km zone landwards) of the Baltic Sea is an
indicator describing not only biomagnifi cation of contaminants but also persecution, disturbance of nest
sites, food availability and availability of suitable nesting sites. Thus, it describes in reproductive terms the
growth rate and condition of the population and indirectly indicates the potential for increased abundance.
5. Functional group or habitat type
Top predatory birds
6. Policy relevance
Descriptor 1, criterion 1.3 Population condition
Descriptor 4, criterion 4.1 Productivity of key species or trophic groups
7. Use of the indicator in previous assessments
Used in the HELCOM “Predatory bird health”-indicator. For more detailed descriptions see the “Predatory
bird health”-indicator fact sheet (2009)
8. Link to anthropogenic pressures
Scientifi cally established links to hazardous substances.
9. Pressure(s) that the indicator refl ect
Directly linked to inputs of synthetic and non-synthetic compounds, disturbance and habitat loss
10. Spatial considerations
The parameters should be sampled only from the 15 km coastal zone.
Assessment units can be sub-basin wide coastal strips (per country), where an average productivity is
calculated.
11. Temporal considerations
Frequency: can be updated annually
12. Current monitoring
Monitored in Sweden, Germany and in Finland. Data on breeding attempts, breeding success and
brood size are collected at as many nests as possible. Early season air surveys are made to fi nd breeding
attempts in Sweden. These are later followed up by nest visits to check success and number of young.
13. Proposed or perceived target setting approach with a short justifi cation.
Historical data exists that has been used for setting the GES boundary. GES boundary exists for Sweden
and can tentatively be used in other areas.
Introduction
The white-tailed sea eagle is a species that faced strong persecution in the 19th and early 20th century
causing the population to crash by early 20th century. Protection measures increased the population, but
in 1950s’ the population crashed again because of organic pollutants, mainly DDT, which caused egg-shell
changes (including thinning) and, hence, wide-spread failure in reproduction.
The white-tailed sea eagle was the fi rst species that signaled the deleterious effects from environmental
pollutants in the Baltic Sea. If white-tailed sea eagle reproduction had been monitored earlier during the
20th century, the negative impact of DDT could have been signaled as early as in the 1950s in the Baltic
Sea. The sea eagle is the ultimate top predator of the Baltic ecosystem, feeding on fi sh, sea birds as well as
on seals, and is thus strongly exposed to persistent chemicals that magnify in the food web.
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