Results and Confidence

This indicator is based on the main parameter 'abundance of breeding waterbirds' and also takes into account the supporting parameter 'breeding success'. The abundance parameter follows the OSPAR Ecological Quality Objective (EcoQO) procedure for the status of seabirds in the North Sea (ICES 2008, 2013, OSPAR/HELCOM/ICES 2016), whereas the breeding success parameter is being developed separately.

 

Abundance – Whole Baltic Sea scale

The abundance component of the indicator is based on counts of breeding pairs, nests or individuals belonging to a breeding population. After testing the indicator concept for selected breeding waterbirds in the Baltic earlier (Herrmann et al. 2013), the indicator has now been applied to a broader spectrum of waterbird species.

The analysis, spanning the reference period (1991-2000) and the assessment period (2011-2016), is based on data of 30 waterbird species, of which one (barnacle goose) could only be analysed on the spatial level of Baltic Sea subdivisions (i.e. not at the scale 1 whole Baltic Sea level).

In 24 of the 29 species assessments for the entire Baltic Sea, the geometric mean of index values in the assessment period (2011-2016) deviated less than 30% (species laying two eggs per year) or 20% (species laying one egg per year) downwards from the modern baseline defined as the average index values in the reference period 1991-2000. These 24 species are estimated to be in a good status. However, five species deviated more than 30% downwards from the baseline, which indicates that they are not in a good status..

The status assessments for the species groups give diverging results. Breeding waterbirds of four species groups achieved the threshold value of 75% of species deviating less than 30%:

  • surface feeders: 9 out of 10 (90%) species' index values deviate less than 30% ,
  • pelagic feeders: 7 out of 7 (100%) species' index values deviate less than 30% (including razorbill and common guillemot deviating less than 20%),
  • benthic feeders: 3 out of 4 (75%) species' index values deviate less than 30% and
  • grazing feeders: 2 out of 2 (100%) species' index values deviate less than 30%.

In contrast, one species group failed to achieve the threshold value of 75% of species deviating less than 30%:

  • wading feeders: 3 out of 6 (50%) species' index values deviate less than 30%.

Index values of the species included in the assessment are listed in Results table 1 and can be used for national MSFD reporting for those HELCOM Contracting Parties that are also EU Member States.

Species failing to achieve the threshold level (deviate more than 30%) in the years 2011-2016 were the velvet scoter, great black-backed gull, pied avocet, turnstone and dunlin.

Species that increased so much that their average index value for 2011-2016 exceeds 130% of the baseline level, which according to the indicator concept are reported as a signal for possible imbalance in the environment, were to a large extant fish-eating species: the great crested grebe, common guillemot, black guillemot, sandwich tern, common tern and Arctic tern.

Results table 1 presents trends calculated for the whole period (1991-2016), with details listed in Results table 2 as information to support the interpretation of the status results in a more long-term perspective. Though still indicating good status, three species are significantly declining (common eider, goosander and common gull). All species not achieving good status in the indicator status evaluation also show significantly declining trends, most strongly in dunlin and great black-backed gull. Out of the 29 species assessed, 11 show significant positive trends, eight significant negative trends, while nine species appear to be stable, and for one species the result is uncertain.

Graphs showing index values are provided in Results figure 1.                                     

The method of analysis applied did not give results for barnacle goose at the whole Baltic Sea scale as its TRIM model was not possible to estimate.

The abundance parameter evaluates data from regular monitoring activities of the coastal countries, but also includes data from some other sources and surveys. If a wider scope would be aimed for, the indicator could be updated using more data from additional sites and stemming from various mapping activities outside regular monitoring programmes. Such a filling of gaps in the regular monitoring with additional data sources could improve the confidence and coverage of the indicator evaluation in the future.


Results table 1. Evaluation of the status of breeding waterbirds in the entire Baltic Sea for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). Good status is shown by green colour, if in individual species the threshold level of 0.7 (0.8 in species laying only one egg per year: razorbill, common guillemot) is met for the geometric mean 2011-2016 and for species groups if at least 75% of the species are in good status. If the index value exceeds 1.3 indicating a large abundance increase the status is still considered good but indicated in orange. Red colour means that the species or the species groups is not in good status. Trends for the period 1991-2016 are shown as ↑ (moderate increase), → (stable), ↓ (moderate decline) and ↓↓ (strong decline), with * when p<0.05 and ** when p<0.01 (?: uncertain; for details see Results table 2).

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Results table 2. Trends observed in breeding waterbirds in the entire Baltic Sea 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Results figure 1a.png

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Results figure 1. Index graphs showing annual index values for breeding waterbirds in the entire Baltic (black line) and 95% confidence intervals (grey shading) resulting from TRIM analyses after rescaling the annual indices to reference level where average of index values 1991-2000 is 1 (thin black line). Further shown are thresholds for good status (70% of baseline, 80% of baseline in species laying only one egg per year, thin red line) and the average index values 2011-2016 (geometric mean) used for the evaluation (red line). In addition, trend slopes and s.e. as well as the status of the species are given below the graphs. 


Abundance – Baltic Sea sub-divisions

The status of breeding waterbirds was also analysed on a smaller regional spatial scale, i.e. based on aggregations of sub-basins to form seven subdivisions (based on HELCOM assessment unit level 2, see Assessment Protocol). As not all species are breeding in each of these subdivisions, the number of species assessed per subdivision is smaller than for the entire Baltic Sea. The analyses followed the same protocol as for the entire Baltic Sea assessment.

 

Kattegat

In the Kattegat, only 50% of the 14 waterbird species assessed passed the threshold value and therefore the breeding waterbirds did not achieve a good status in the period 2011-2016 (Results table 3). The same holds true for surface feeders (good status in 3 out of 7 species, 43%) and wading feeders (all 3 species not in good status), whereas a good status was observed in pelagic feeders (4 out of 4 species above threshold). Owing to lacking data the status of benthic feeders and grazing feeders could not be assessed.


Results table 3. Evaluation of the status of breeding waterbirds in the Kattegat for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.


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Out of the seven species not in good status, six showed significant declines over the period 1991-2016, most strongly observed for the common gull and dunlin (trend for ringed plover uncertain, Results table 4). Species in good status were either stable or increasing, with the steepest increase observed in common guillemot. The trends of individual species are depicted in Results figure 2 (Annex 1).

 

Results table 4. Trends observed for breeding waterbirds in the Kattegat 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Belt Group

In the Belt Group (Great Belt, The Sound), only two species (great cormorant, Arctic tern) did not reach the threshold level, thus with a pass rate of 83% the breeding waterbirds showed an overall good status (Results table 5). With pass rates of 88% (surface feeders) and 100% (wading feeders, grazing feeders), good status was found for these three species groups, whereas pelagic feeders failed (1 out of 2 species in good status, 50%) and benthic feeders could not be assessed due to a lack of data.

 

Results table 5. Evaluation of the status of breeding waterbirds in the Belt Group for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.

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Negative trends (1991-2016) were not only observed in the two species in bad status, but also in common gull and pied avocet, of which the index values still reflect good status. A very steep increase was experienced by barnacle goose (Results table 6). The trends of individual species are depicted in Results figure 3 (Annex 1).

 

Results table 6. Trends observed in breeding waterbirds in the Belt Group 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Bornholm Group

In the Bornholm Group (Kiel Bay, Bay of Mecklenburg, Arkona Basin, Bornholm Basin), half of the 24 species assessed did not reach the threshold level, and therefore breeding waterbirds did not achieve good status (Results table 7). On the level of species groups, only the grazing feeders attained good status, with both of the two species assessed passing the threshold. Much lower pass rates reveal bad status of surface feeders (44%, 9 species), pelagic feeders (50%, 6 species), benthic feeders (50%, 2 species) and wading feeders (40%, 5 species).

 

Results table 7. Evaluation of the status of breeding waterbirds in the Bornholm Group for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.

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Out of 12 species in bad status, nine showed significant declines (most steeply in dunlin), while the trend remained uncertain in three species (Results table 8). Most of the other species were stable or increased, but mute swan and Eurasian oytercatcher declined significantly despite their good status based on index values. The steepest increase was observed in lesser black-backed gull. The trends of individual species are depicted in Results figure 4 (Annex 1).


Results table 8. Trends observed in breeding waterbirds in the Bornholm Group 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Gotland Group

In the Gotland Group (Gdansk Basin, Eastern Gotland Basin, Western Gotland Basin, Gulf of Riga), 16 out of 27 species (63%) passed the threshold level, but the limit of 75% of species necessary for an overall good status of breeding waterbirds was not met (Results table 9). The only species group in good status are the pelagic feeders with 6 out of 7 species (86%) in good status. This goal was not reached by surface feeders (63%, 8 species), benthic feeders (33%, 3 species), wading feeders (33%, 6 species) and grazing feeders (67%, 3 species).

 

Results table 9. Evaluation of the status of breeding waterbirds in the Gotland Group for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.

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All species not in a good status showed significant negative trends (Results table 10). Five of them (great black-backed gull, herring gull, lesser black-backed gull, common eider, turnstone) were even declining steeply. On the other hand, most of the species in good status were stable or increased, with the exception of greylag goose and goosander, which declined significantly. The trends of individual species are depicted in Results figure 5 (Annex 1).


Results table 10. Trends observed in breeding waterbirds in the Gotland Group 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Åland Group

In the Åland  Group (Northern Baltic Proper, Åland  Sea), 16 out of 23 species (70%) were in a good status in the assessment period (2011-2016), thus breeding waterbirds failed to achieve an overall good status (Results table 11). With an 80% pass rate each, pelagic feeders (5 species) and wading feeders (5 species) were indicated to be in good status. This was only narrowly missed for surface feeders (71%, 7 species) and grazing feeders (67%, 3 species), whereas benthic feeders failed the threshold more clearly (33%, 3 species).

 

Results table 11. Evaluation of the status of breeding waterbirds in the Åland  Group for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.

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Out of the seven species in bad status, trend analysis revealed stability for black guillemot, but all the other species were significantly declining from 1991 to 2016 (steep declines in common eider and herring gull, Results table 12). While a steep increase was observed in Caspian tern and others were increasing moderately, significant declines were noticed in goosander and razorbill despite of being in good status in the assessment period (2011-2016). The trends of individual species are depicted in Results figure 6 (Annex 1).

 

Results table 12. Trends observed in breeding waterbirds in the Åland  Group 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Gulf of Finland

Only 11 out of 21 species (52%) achieved the threshold level, therefore breeding waterbirds did not achieve an overall good status in the Gulf of Finland in the years 2011-2016 (Results table 13). The only species group in good status was grazing feeders (all 3 species passing threshold). All the other groups did not reach the threshold of 75% of species in good status: surface feeders (17%, 6 species), pelagic feeders (67%, 6 species), benthic feeders (33%, 3 species) and wading feeders (67%, 3 species).

 

Results table 13. Evaluation of the status of breeding waterbirds in the Gulf of Finland for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.

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Out of 10 species in bad status, seven were significantly decling (steeply in the case of goosander), one showed stability and for two the trends remained uncertain (Results table 14). The species in good status mostly increased or the trend remained uncertain, but Eurasian ostercatcher was stable and common eider even declined (Table 14). The steepest increase was noticed for barnacle goose. The trends of individual species are depicted in Results figure 7 (Annex 1).

 

Results table 14. Trends observed in breeding waterbirds in the Gulf of Finland 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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Bothnian Group

In the Bothnian Group (Bothnian Sea, The Quark, Bothnian Bay), only 3 out of 19 species failed to pass the threshold level. As 84% of the breeding waterbird species were in good status, an overall good status was determined (Results table 15). While all species (100%) and therefore the respective species groups were in good status in surfaces feeders (7 species), pelagic feeders (2 species) and grazing feeders (3 species), this was not the case in benthic feeders (67%, 3 species) and wading feeders (50%, 4 species).

 

Results table 15. Evaluation of the status of breeding waterbirds in the Bothnian Group for the period 2011-2016. Index values (single years and mean) are scaled to the average of the reference period (1991-2000, index value set to 1). For explanation see Results table 1.

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Turnstone was the only species declining in the period 1991-2016, whereas most others were increasing (most steeply the barnacle goose, Results table 16). For some species, the trend analyses indicated stable population sizes, including the common eider, which did not reach good status. The trends of individual species are depicted in Results figure 8 (Annex 1).

 

Results table 16. Trends observed in breeding waterbirds in the Bothnian Group 1991-2016. Trend slopes and standard errors result from TRIM analyses.

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It is obvious from the results of both the whole Baltic Sea and in the seven subdivisions that the welfare of waterbird species varies considerably between and within species groups. Therefore, it is difficult to derive simple conclusions from the indicator results. It is known from a number of case studies that the development of population sizes are subject to a large variety of impacting factors. JWGBIRD has explored impacts on breeding waterbirds at the Baltic Sea coast and found that direct influence from human activities is relatively scarce, with tourism and leisure being the pressure affecting the largest number of species (OSPAR/HELCOM/ICES 2018). More importance was assigned to more natural drivers, as many breeding species are influenced by predation, habitat change and prey availability. However, even the natural drivers are not independent from anthropogenic pressures. For example, fishing has considerable impact on the composition of the Baltic fish fauna, and the removal of competitive large fish has promoted piscivorous waterbirds, as expressed by positive trends in this indicator. Declining waterbird populations often suffer from predation of eggs and chicks, which is partly caused by introduced predators such as American mink and raccoon dog (HELCOM 2013). On the other hand, the strong increase of an indigenous predator, the white-tailed sea eagle, has negative impacts on the breeding population of common eiders (and probably other waterbirds) through the removal of indviduals and the failure of broods (Ekroos et al. 2012). As many species are influenced by several natural and anthropogenic drivers, indicator results have to be examined carefully in order to draw appropriate conclusions and implement suitable management measures.

 

Breeding success

The status evaluation based on the breeding success parameter of the indicator is poorly developed. No current results can yet be presented. There are no operational country-wide monitoring scheme which could currently supply data for the evaluation, although productivity is observed in several case studies (Herrmann et al. 2013). Therefore, this part of the indicator has been regarded as only providing qualitative support to the status evaluation based on the abundance of breeding waterbirds parameter. If monitoring schemes covering a number of waterbird species are available, it could be relevant to construct the breeding success parameter as an independent indicator with its own threshold value comparable to the operational indicator in the OSPAR region (ICG-COBAM MSFD Indicator B-3 'Breeding success/failure of marine birds', OSPAR 2017b).

Breeding success can directly show the suitability of prevailing environmental conditions for the reproduction of waterbirds. Whereas the bird abundance parameter alone may react slowly to changes in the environment owing to the high longevity of the individuals of the population, breeding success reflects short-term changes much better and could potentially act as an "early warning system". For example, decreased food availability would directly translate into breeding failure as soon as a certain threshold is no longer met. As long as marine food is taken for chick provisioning, the marine ecosystem can thus be evaluated by the reproductive output in relation to reference values. However, breeding failure is often connected to predation. As this mainly involves terrestrial mammals, a breeding success indicator reflects the conditions in the coastal landscape as well. Therefore, evaluations based on measurements of breeding success have to include careful considerations about the reasons responsible for breeding failure. As the drivers behind changes in population sizes are often either unknown or very complex, monitoring of reproduction would potentially improve our understanding very much.

 

Confidence of the indicator status evaluation

The overall confidence of the indicator is currently intermediate.

Regarding the temporal coverage, the confidence is high because data from all years of the assessment period (2011-2016) are included. However, not all species are monitored in each country annually. Commonly found intervals are three or six years (as adaptation to Natura 2000 reporting cycles, see European Commission 1992, 2010) or even ten years. This results in many missing data for part of the years in the dataset. Although TRIM is designed to handle this by imputing the missing data, the analysis needs a substantial amount of yearly "real" data to calculate reliable imputed values. Missing counts for particular sites are estimated (´imputed´) from changes in all other sites. If there are too few of these "other sites" with "real" data, the obtained estimates for focal sites are strongly influenced by site-specific processes at the sites providing the real data.

The spatial representability is estimated to be intermediate, because this evaluation is lacking information from two Contracting Parties of HELCOM (Lithuania, Russia) and contains only fragmentary information from Latvia. Therefore, the current analyses are based on unevenly distributed sites around the Baltic Sea.

The accuracy of the estimate is high, because the results clearly show whether or not the threshold values are met. The reference period (1991-2000) used to define the modern baseline for the indicator is arbitrarily chosen to reflect as early abundance data as possible. The modern baseline does not reflect pristine conditions. In order to enhance the confidence in the overall threshold values, future work to explore the abundance of the baseline period in relation to pristine conditions could be undertaken.

Methodological confidence can be regarded as intermediate. Though there are no HELCOM guidelines for monitoring breeding bird abundance, the methods applied in breeding bird surveys can be expected to meet international agreed standards and to result in data qualities according to at least local standards.