Key message figure 1. Status assessment results based evaluation of the indicator 'white-tailed sea eagle productivity'. The assessment was carried out using aggregated Scale 3 HELCOM assessment units (for more information see appendix 1 and the HELCOM Monitoring and Assessment Strategy Annex 4). Assessment for each individual Scale 3 unit was not possible because of small sample sizes in many units. Although numbers of breeding white-tailed sea eagles are still increasing, eagles are territorial which limits breeding density – hence the need for custom assessment units. Note that this indicator is a "one-out, all-out" indicator. Although productivity parameter only failed the threshold value in one region, four additional units failed one of the other variables, meaning that a total of five units did not achieve the threshold. Good status was achieved in six units. The indicator is applicable, but not evaluated, in a few regions where sample sizes are very low at present. Click here to access interactive maps at the HELCOM Map and Data Service: White-tailed sea eagle productivity.
This core indicator assesses the status of white-tailed sea eagle reproduction by evaluating the parameter 'productivity' and the two supporting variables 'brood size' and 'breeding success'. The indicator reflects an environment un-disturbed by hazardous substances when all three parameters in an assessment unit achieve their respective threshold values. The status of the white-tailed sea eagle productivity has been evaluated for the period 2011-2016 in most areas (2011-2014/2015 for Sweden, where later data is at the quality control stage). There are 13 custom assessment units for this indicator, and 11 were evaluated. Two units were not included in the evaluation due to very low sample sizes, awaiting future population increases before inclusion in the evaluation process.
The productivity of white-tailed sea eagles achieved the threshold value, and therefore good status, in six assessment units (Key message figure 1). Five units did not reach one or more threshold value(s), therefore being classified as not good status. This was mainly due to the failure to achieve the threshold value in at least one of the underlying variables of the indicator: brood size and/or breeding success. This indicator is a "one-out, all-out" indicator and all three components must reach the respective threshold values in order to achieve good status. The evaluation shows that nestling brood size was not achieved in four out of 11 evaluated regions, and future studies should focus on this component of the indicator.
Breeding success was above the threshold value in all regions except one (Finland, Archipelago Sea, Åland+Åbo-region, see figure 1). Only in one region was productivity itself below the threshold value (Germany, represented by Mecklenburg-West Pomerania).
The significantly higher occurrence of dead eggs in the Swedish part of the Bothnian Sea compared to other areas might indicate a higher impact from hazardous substances. During the period covering this evaluation, extremely high concentrations, particularly of DDE and PCBs, have been found in eggs from the Swedish Bothnian Sea, also showing damage to egg shell structure. This clearly warrants further study, but it must be noted that population growth does not seem to be affected by hazardous substances at present.
It should be noted that no white-tailed sea eagles breed in the innermost part of the Gulf of Riga.
The confidence of the indicator status evaluation is considered to be high.
The indicator is applicable in the coastal waters of all the countries bordering the Baltic Sea, up to 10 kilometres from the coast line.
As predators at the top of the aquatic food chain, white-tailed sea eagles are highly exposed to hazardous substances that accumulate and magnify through the food web and can thus serve as sentinels for the effects of harmful substances. The elevated concentrations of persistent chemicals in white-tailed sea eagles also give possibilities to detect new emerging pollutants that are below detection limits in other biota.
The white-tailed sea eagle was the first species to signal the effects of persistent chemicals in the Baltic Sea environment. By the 1970s its population was reduced to one fifth of the pre-1950 background level due to the effects of contamination from hazardous substances. The detection of PCB in Baltic white-tailed sea eagles occurred in 1966. After measures were implemented to ban the use of DDT and PCB, the reproductive success began improving after a delay of approximately a decade. The productivity reached that of a reference level by the mid-1990s, clearly exemplifying a case where the effects of environmental management actions are reflected in an improved environmental status.
D8C2. The health of species and the condition of habitats (such as their species composition and relative abundance at locations of chronic pollution) are not adversely affected due to contaminants including cumulative and synergetic effects.
D1C3. Population condition (fecundity rates).
D4. Food webs
D4C4 .Productivity of the trophic guild is not adversely affected due to anthropogenic pressures.
Other relevant legislation: In some Contracting Parties also:
HELCOM (2018) White-tailed sea eagle productivity. HELCOM core indicator report. Online. [Date Viewed], [Web link].
White-tailed eagle productivity HELCOM core indicator 2018 (pdf)