Marine bird abundance

The UK target for population size of non-breeding waterbirds was met in the Greater North Sea but not in the Celtic Seas. The target was not met for breeding seabirds in either sub-regions.

Background

UK target on marine bird population size

This indicator is used to assess progress against the following target, which is set in the UK Marine Strategy Part One (HM Government, 2012): “At the scale of the Marine Strategy Framework Directive sub-regions, the abundance of marine birds is not significantly affected by human activities. Changes in abundance of marine birds should be within individual target levels in 75% of species monitored.”

Key pressures and impacts

The main offshore pressures on seabirds arise from climate change and from fishing. Climate-driven shifts in the food chain have combined with the previous over-fishing, reducing the availability of small fish that seabirds feed on, such as lesser sandeels. Conversely, some species have previously benefited from food provided by the fishing industry through discards and may suffer because of new regulations that aim to eliminate discards. Surface-feeding seabirds, in particular, fulmars , ingest floating plastic particles, which is likely to have a negative effect on their health, though the impact of plastic pollution on seabird populations is currently unknown. The main pressures on waterbirds arise in coastal waters. They include contamination by hazardous substances, competition with shellfish harvesting, disturbance, and habitat loss. Climate change has also driven change in waterbird numbers by increasing winter survival and enabling a greater number to spend the winter further north and east within the UK and Europe.

Measures taken to address the impacts

Measures to protect seabirds from human activities are set out in the UK Marine Strategy Part Three (HM Government, 2015). These include those taken under the EU Birds and Habitat Directive (European Council 1992), the Common Fisheries Policy and UK By-catch plans. Management measures at Special Protected Areas and Marine Protected Areas are likely to help reduce impacts from human activities and thus increase the resilience of seabirds facing the negative impacts of climate change. Management measures at protected sites for waterbirds are aimed at reducing disturbance from human activities such as recreation, bait digging, and shellfish harvesting and from predators such as foxes.

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Further information

This indicator includes information on marine bird species that, at some point in their annual life cycle, are reliant on coastal and/or offshore marine areas. The indicator is constructed from species-specific trends in annual abundance and includes:

1. seabird breeding abundance, estimated from counts of birds or pairs on land at breeding colonies or sites, nesting close to the coast, and using the marine environment for example, as their food source)
2. waterbird non-breeding abundance, estimated from counts of birds in intertidal areas or close to the shore and counted from land or from the air during migration or over the winter.

In this context ‘seabirds’ consist of petrels and shearwaters (Procellariiformes), gannets and cormorants (Suliformes), skuas, gulls, terns and auks (Charadriiformes), and ‘waterbirds’ consist of shorebirds (order Charadriiformes), ducks, geese and swans (Anseriformes), divers (Gaviiformes), and grebes (Podicipediformes).Seabirds spend most of their lives at sea, feeding on prey such as plankton, fish, and squid that live within the water column or picking detritus from the surface. Cormorants, gulls, and terns tend to be confined to inshore waters, whereas petrels, shearwaters, gannets, skuas and auks venture much further offshore and beyond the shelf break. Most seabirds are assessed using breeding abundance, because they are much easier to count when they aggregate on land to breed than when they are dispersed at sea over large areas. Abundance indicators could also be constructed from timeseries data collected at sea, but few data were available to be able to do so on this occasion.

Waterbirds, depending on the species, feed on land, above and below the high-water mark and in shallow areas offshore. Shorebirds, some duck species, and some gulls feed on benthic invertebrates in soft intertidal sediments and on rocky shores. Geese graze on exposed eelgrass beds (Zostera spp) as well as coastal marshes. Divers, mergansers, and grebes feed on fish in shallow inshore waters, in which diving duck species such as scoter also forage on invertebrate benthos like bivalves.

Most waterbirds are assessed using non-breeding abundance, because they are much easier to count when they are migrating or during the winter when they aggregate in intertidal and inshore areas. Waterbirds tend to be much more difficult to count during the breeding season because most species do not tend to breed colonially, and nesting pairs are distributed over large areas. Many waterbird species in this assessment breed inland and areas outside the OSPAR Maritime Area.

Assessment method

This UK assessment uses the same methods and data as the OSPAR Intermediate Assessment (OSPAR Commission, 2017), for which the indicator development was led by the UK. The targets and thresholds used in this indicator assessment were developed for breeding seabird abundance data to assess the OSPAR Ecological Quality Objective on seabird population trends as an index of seabird community health (ICES, 2008, 2010, 2011, 2012). This indicator differs from the original Ecological Quality Objective because it incorporates data on more species, including waterbirds and also uses data on non-breeding abundance. This indicator has gone through extensive testing and development (see ICES, 2013a; 2013b; 2013c; 2013d, 2015).

This indicator assessment begins by constructing a time-series of annual estimates of ‘relative breeding abundance’ or ‘relative non-breeding abundance’ for each species in each Marine Strategy Framework Directive sub-region or sub-division thereof (see spatial assessment units below). This UK indicator assessment is confined to the Greater North Sea and the Celtic Seas. The assessment of the Greater North Sea includes both breeding and non-breeding data from all countries bordering the sub-region, except France. The assessment of the Celtic Seas is based on breeding data from Ireland and the UK and non-breeding data from the UK only. The assessment of this indicator for the OSPAR Intermediate Assessment (OSPAR Commission, 2017) also included the Arctic Waters of Norway, which provides a useful comparison with this UK assessment because some species breed in all three regions and some species which breed in the Arctic over-winter in UK waters.

For this UK assessment in the Greater North Sea, species were only included in the indicators if sufficient data were available from sites in the UK. Great cormorant was the only species for which data on breeding abundance and non-breeding abundance were available. Relative abundance is the number of birds or breeding pairs estimated each year as a proportion of a baseline. Each species-specific estimate of annual relative abundance is compared against thresholds. This indicator assessment is based on the proportion of species in a region or sub-division that have exceeded thresholds for relative abundance in the most recent year of the time series. Separate assessments were carried out for breeding relative abundance and non-breeding relative abundance.

Species-specific indicators of relevance abundance

Data acquisition

In 2016, the following data were requested from Contracting Parties on counts of breeding and non-breeding birds collected during the period from 1980 to 2015:

1. Breeding seabird colonies and breeding waterbirds nesting close to the coast and using the marine environment (for food, for example): counts of breeding pairs (or if not available counts of adults) per species per colony per year.
2. Wintering and migrating waterbirds: numbers of birds, per species, per site, and per year that are counted from the land or the air. These data consisted mostly of maximum or single counts conducted in January (except for North of the Arctic Circle where counts are conducted in March when there is sufficient daylight to do so). Data from the Wadden Sea Trilateral (Germany, the Netherlands, and Denmark) Monitoring and Assessment Programme and the UK Wetland Bird Survey also consisted of a mean of counts conducted throughout a year: from July in one year to June in the next

Most data refer to individual colonies or sites rather than large stretches of coastline. Exceptions are the Wadden Sea, the Dutch Delta and for non-breeding data in the UK, where colonies have been aggregated to regions and sub-divisions.

Spatial aggregation

Separate indicator assessments were conducted for each species in each sub-region. An assessment was also conducted for each sub-division of the Greater North Sea (Figure 1). These smaller sub-divisions may help to interpret the assessment results. The boundaries of the sub-divisions are based on a coarse assessment of the main oceanographic features such as currents and depths, and some relatively clear-cut differences in seabird/waterbird community structures and population trends (ICES, 2013c; 2013d).

Figure 1. Marine Bird assessment units. North Sea sub-divisions: a) Northeast coast of Britain, b) West coast of Norway, c) Skagerrak and Kattegat, d) Southern North Sea, e) The English Channel, f) North coast of Scotland and the Northern Isles.

Data used in this assessment

This UK indicator assessment was undertaken in the entire OSPAR Regions (approximate to each Marine Strategy Framework Directive Sub-region) of the Celtic Seas using data from the UK, Ireland, and the Isle of Man; and in the Greater North Sea using data from the UK, the Channel Islands, the Netherlands, Belgium, Germany, Denmark, Sweden and Norway. This large scale is relevant because almost all the species included in this assessment are highly mobile and migratory.

When all data from other countries had been collated, it became clear that before 1991, the number of annual counts per site was much lower in some areas, with many sites not being surveyed at all. A large amount of these early data would need to be interpolated and our confidence in the accuracy of trends in abundance during this period would be very low. For this reason, this indicator assessment was restricted to 1991 onwards. In the Celtic Seas, regional scale assessments used data collected between 1991 and 2015. In the North Sea, regional assessments were only possible for 1991 to 2014, because more recent data were not available from the Wadden Sea.

In the Wadden Sea (Denmark, Germany and the Netherlands), the status of non-breeding waterbirds in the area is best indicated by year-to-year changes in the mean of counts conducted throughout the year (from July in one year to June in the next year) (Blew and Südbeck, 2005; Blew and others 2016). These counts are also conducted in the UK and in the Netherlands (outside of the Wadden Sea) but are not carried out elsewhere in the Greater North Sea. All contracting parties supplied maximum or single counts conducted in January. These January counts were used for the indicator assessment in the North Sea Region as a whole and separately, in each Greater North Sea sub-division, apart from the Southern North Sea (sub-division d in Figure 1), where mean year-round counts from the UK, the Netherlands, Germany, and Denmark were used (year-round counts were not available for Belgium). Year-round counts for the Wadden Sea (Denmark, Germany and the Netherlands) were only available up to 2014. Hence, the indicator assessments for each North Sea sub-division were restricted to the period 1991 to 2014.

Trend analysis

This indicator assessment requires an annual estimate of abundance per site or colony for each species. Not all the colonies and sites had been counted every year. In years when no count had been made, abundance was estimated from counts made in other years using statistical models. The minimum number of years of counts for a particular species required for a colony or site to be included in the analysis was set at two for all species except northern fulmar, which was set at a minimum of five years (ICES, 2010, 2011). Some OSPAR Contracting Parties provided data that had no missing values because these had already been interpolated before submission, using published methods:

1. UK non-breeding abundance, all species (for details of methods see Underhill and others, 1994)
2. Denmark, Germany and the Netherlands in the Wadden Sea (North Sea sub-division d) non -breeding abundance, all species (for details of methods see Blew and Südbeck, 2005; Blew and others 2016; The Joint Monitoring of Migratory Birds Program)
3. Denmark, Germany and the Netherlands in the Wadden Sea (North Sea sub-division d) breeding abundance, all species. For details of methods on breeding birds – see Koffijberg and others , 2015,and The JMMB Program

For all other data submitted by Contracting Parties, missing annual observations were interpolated using a modified chain method (Thomas, 1993). This method estimates values of missing observations based on information in other years and sites. The advantage of this method is that it allows for site-specific variation at each site, thereby avoiding the conventional assumption that changes in abundance at different sites occur synchronously. A further advantage of this approach is that it can easily incorporate counts of whole colonies and counts from smaller plots within the same colonies that are monitored more frequently than the whole colony. ‘The Thomas estimation method’ has been used to construct trends in abundance for earlier iterations of this indicator and its Ecological Quality Objective predecessor. Details of the method are given in Annex 3 of ICES, 2008.

Applying regional weightings to abundance trends

Not all the colonies or sites in an assessment unit will be monitored and present in the dataset. The proportion of a population that is monitored varies between species and between countries. There is a resultant bias, in that those countries where few sites are monitored are under-represented in the resultant trends for a given assessment unit, compared to those countries where a larger proportion of sites are monitored.

To remove such bias, the annual estimates of breeding and non-breeding abundance in each country were weighted according to the size of the population in that country. Each Contracting Party provided recent estimates of total abundance for each species along their coastline within each of the assessment units in Figure 1. To apply a regional weighting, each annual estimate of abundance in each assessment unit was divided by the proportion of the total population that is present within the sites or colonies that are included in the data provided (p in the equation below). The total number of birds or pairs in an assessment unit were, in most instances, taken from the results of national censuses. As an example, the weighted annual breeding abundance of a species in the Celtic Seas, y_CS in year j, was calculated from estimates of abundance in year j, in each constituent country – UK coast within the Celtic Seas sub-region (y_UK-CSj) and Ireland (y_IREj) - as follows where p_UK and p_IRE are the proportions of the respective populations in the UK and Ireland that are contained in the sample of colonies that were monitored in each country in the Celtic Seas:

y_CSj = ( y_UKj / p_UK) +( y_IREj / p_IRE)

Data from some areas contained all the colonies or sites in that area, so regional weightings were not necessary. In Belgium, all the breeding and non-breeding sites in the country are monitored, so no weightings were required for these data. Regional weighting was also not necessary for estimates of annual abundance that had been interpolated before submission. These included trends in breeding and non-breeding abundance in the Dutch, German, and Danish Wadden Sea, and trends in non-breeding abundance in the UK.

Parameter/metric

To compare the state of species that have very different population sizes, estimates of abundance that were measured in numbers of birds or breeding pairs were converted into an indicator metric that uses a single scale (a proportion) for all species. The indicator metric is ‘relative abundance’, which is annual abundance expressed as a percentage of the baseline: relative abundance = annual abundance / baseline abundance

It is preferable to set baselines objectively, by using one of the methods recommended by ICES (ICES, 2015). However, most Contracting Parties did not provide baselines in 2016. As an alternative, relative non-breeding abundance was calculated using a baseline equal to the abundance in the second year of the time series (1992). The start year, 1991, was not used because the first year in an estimated time series is usually less reliable. Therefore, in 1992 the relative non-breeding abundance of all species is equal to one. For relative breeding abundance, the baseline abundance of 1992 was predicted by a linear model fitted to the annual abundance estimates during the period 1991 to 2000. This meant that the baseline abundance in 1992 was not necessarily equal to the annual abundance estimate in 1992. Therefore, the relative breeding abundance in 1992 did not necessarily equal one.

Species selection and aggregation (functional groups)

There were sufficient data to construct species-specific indicators of relative breeding abundance for 22 species and indicators of relative non-breeding abundance for 53 species. Species were assigned to the functional groups given in Table 1. The species assessed and the functional groups to which they were assigned, are listed in the ‘extended Results’ section below.

Table 1. Marine bird functional groups.

Functional group	Typical feeding behaviour	Typical food types	Additional guidance
Wading feeders	Walk/wade in shallow waters	Invertebrates (molluscs, polychaetes, etc.)	Example: oystercatcher
Surface feeders	Feed within the surface layer (within 1 to 2 m of the surface)	Small fish, zooplankton and other invertebrates	“Surface layer” defined about the normal diving depth of plunge-divers (except gannets) Example black-legged kittiwake
Water column feeders	Feed at a broad depth range in the water column	Pelagic and demersal fish and invertebrates such as the squid and, zooplankton.	Include only species that usually dive by actively swimming underwater, but including gannets. Includes species feeding on benthic fish such as flatfish. Example: common guillemot
Benthic feeders	Feed on the seafloor	Invertebrates such as molluscs and echinoderms	Example: common eider
Grazing feeders	Grazing in intertidal areas and shallow waters	Plants such as eelgrass, saltmarsh plants and algae	Geese, swans and dabbling ducks, coot Example: mallard

Assessments

Species-specific threshold

This assessment uses two different thresholds that are designed to reflect the resilience of different species to declines in their populations (ICES 2008, 2010, 2011). It is desirable for the annual relative abundance of a species to be above:

• 0.8 (80 % of the baseline) – for species that lay one egg
• 0.7 (70 % of the baseline) – for species that lay more than one egg.

The reason for these different thresholds is because species that lay only one egg are expected to recover more slowly from declines in population size than species that can potentially produce more than one chick per year. If relative abundance is below the appropriate threshold, it is considered to be in ‘poor’ status and further research or management is recommended, depending on what is appropriate.

An upper threshold of 1.3 (130% of the baseline) was applied to the annual relative abundance of all species. This upper threshold is used to identify potentially disruptive increases in some species that might impact on other species (ICES, 2008). For instance, large predatory seabird species have benefited from the provision of food from fishery discards. The increase in numbers of species such as the great-black backed gull and great skua have, in some areas, led to declines in their prey species such as kittiwake. However, this has the potential to wrongly identify a species as having a detrimental impact on other species when in fact it is in recovery to levels greater than the baseline (ICES, 2010; 2011; 2013c). As a result, this upper threshold is not used as an indicator of status and is only used to provide a trigger for further research or management, if increases in one species are likely to result in decreases of others.

Integration of species-specific assessments

To assess the status of marine bird communities, the proportion of species was calculated exceeding the lower thresholds, as previously used for breeding seabirds in the Ecological Quality Objective on seabird population trends as an index of community health (ICES, 2008). We applied the following integration rule: ‘Changes in abundance of marine birds should exceed species-specific thresholds in 75 % or more species that are assessed’. Humphreys and others (2012) also recommended a value of 75 % for non-breeding shorebirds and coastal breeding waterbirds in the UK because it is comparable to the thresholds used for shorebirds by the Wetland Bird Survey Alerts System.

In this indicator assessment, non-breeding relative abundance and breeding relative abundance were assessed separately. This is because most species in the non-breeding assessment use intertidal and inshore areas, and the majority of species in the breeding assessment are seabirds that use the wider marine environment. The breeding and non-breeding assessments, therefore, indicate impacts from different suites of pressures, operating in different parts of the marine environment.

To provide greater insight into the likely impacts operating on relative non-breeding and breeding abundance, species-specific assessments were integrated at different spatial scales: for each sub-region and sub-division of the North Sea (see Figure 1). Within each sub-region, species-specific assessments were also integrated for each functional group (see Table 2).

Results

Findings from the 2012 UK Initial Assessment

This indicator, thresholds and targets were not used during the UK’s Initial Assessment, but the following conclusions were made:

1. Although numbers of seabirds breeding in the UK had increased from around 4.5 million in the late 1960s to 7 million by the end of the 1990s, mainly as a result of increased protection from hunting and persecution in the UK and overseas, recent downward trends in the Greater North Sea and the Northern Celtic Seas were of concern.
2. The average abundance of waterbird species wintering in or migrating through marine areas in the UK doubled between the mid-1970s and the mid-1990s. By the winter of 2007, average abundance declined to 185 % of what it was in the mid-1970s when co-ordinated monitoring began.

Latest findings

Status assessment

Table 2 shows the proportions of species that achieved their respective thresholds (> 0.7 or 0.8) for relative breeding abundance in 2014 and 2015, and for relative non-breeding abundance in 2015 in each sub-region, against the UK target of 75% or more of species. In the Greater North Sea, the UK target was partially met: 78% of waterbird species met the thresholds for non-breeding abundance, but only 59% of seabird species did so for breeding abundance. In the Celtic Seas, the UK target value of 75% of species, was not met for both breeding seabirds (63%) and non-breeding waterbirds (53%). The species of seabird that have not met thresholds for relative breeding abundance are shown as red in Figure 2.

Table 2: Percentage of species assessed that had a relative abundance in 2015 above the species-specific threshold values (0.7 or 0.8), in each functional group in the Greater North Sea (2014) and the Celtic Seas.

	Percentage of species above thresholds for relative abundance
	Greater North Sea		Celtic Seas
Functional group	Breeding	Non-breeding	Breeding	Non-breeding
Wading feeders		82% (22)		47% (19)
Surface feeders	47% (15)	100% (1)	50% (12)	100% (1)
Water column feeders	86% (7)	83% (6)	86% (7)	50% (4)
Benthic feeders		56% (9)		50% (8)
Grazing feeders		88% (8)		63% (8)
Breeding/non-breeding total	59% (22)	78% (46)	63% (19)	53% (40)
All	72% (68)		56% (59)

Figure 2. Species–specific assessment of relative breeding abundance of seabirds in 2014 in the Greater North Sea and in 2015 in the Celtic Seas. Species grouped by functional group.

Trend assessment

For breeding seabirds, the proportion of species exceeding thresholds for relative abundance has remained stable but below the target of 75% since the time of the initial assessment in both the North Sea and Celtic Seas (late 2000s, Figure 3). For non-breeding waterbirds, the proportion of species exceeding thresholds for relative abundance has declined sharply below 75 % in the Celtic Seas and has declined less so in the North Sea, where it has been above 75 %, except in 2010 (Figure 3). The numbers of species considered for relative breeding abundance were 22 and 19 in the Greater North Sea and Celtic Seas, respectively, and for relative non-breeding abundance 46 and 40 in the Greater North Sea and Celtic Seas, respectively. There was moderate confidence in both the methodology and the data used in this assessment.

Figure 3: Changes in the annual proportion of species meeting targets for a) relative breeding abundance and b) non-breeding abundance, during 1992 to 2015. The bold horizontal line denotes the target threshold of 75 % or more. The number of species.

Further information

Species-specific assessments

Species specific assessments of relative non-breeding abundance are shown in Figure 4. This figure is analogous to the relative breeding abundance results in Figure 2.

Figure 4. Species–specific assessment of relative non-breeding abundance in 2014 in the Greater North Sea and in 2015 in the Celtic Seas. Species grouped by functional group.

Examples of the region and species-specific trends in breeding abundance and in non-breeding abundance on which this indicator assessment is based, are shown in Figures 5 and 6. Trends were estimated at various spatial scales (. sub-regions and for sub-divisions thereof), depending on there being sufficient data available, for which the trends were estimated for each species. The assessments of each species in 2014 or 2015 presented in Figures 2 and 4 , are broken down into the sub-divisions of the North Sea in Figures 7 and 8. The number of species included in the sub-divisional assessments are fewer than those in the regional assessments because there are fewer colonies and sites at the smaller scales that have data from a sufficient number of years. There was only one species included in the assessment for the Celtic Seas and the North Sea for which breeding and non-breeding abundance were both be assessed.

Figure 5. Atlantic Puffin: example of species-specific trends in relative breeding abundance in each sub-region (approximate to OSPAR Region) and sub-division (shown in Figure 1) from 1991 to 2015. The baseline is where relative abundance = 1.0. Black dotted line indicates the lower threshold of 0.7 (for species that lay more than 1 egg) or 0.8 for species that lay one egg only); the black dashed line indicates the upper threshold of 1.3.

Figure 6. Species-specific trends in relative non-breeding abundance in each sub-region (approximate to OSPAR Region) and sub-division (shown in Figure 1) during 1991 to 2015, except where data are only available in 1991 to 2014 for all parts of the Greater North Sea. Trends presented for both sub-regions and r region II sub-divisions a-c, e, f, are derived from counts in January of each year. Trends for North Sea sub-division d are derived from the annual mean of counts conducted throughout the year (July – June). The baseline is where relative abundance = 1.0. Black dotted line indicates the lower threshold of 0.7 (for species that lay more than one egg) or 0.8 for species that lay one egg only); the black dashed line indicates the upper threshold of 1.3.

Figure 7. Species–specific assessment of relative non-breeding abundance in 2014 in the sub-divisions of the Greater North Sea (see Figure 1).

Figure 8. Species–specific assessment of relative breeding abundance in 2015 in the sub-divisions of the Greater North Sea (see Figure 1).

Conclusions

The UK target for population size was met for only non-breeding waterbirds in the Greater North Sea: the abundance of more than 75% of species assessed was sufficiently close to or above the baseline set in 1992. The UK target was not met in the North Sea for breeding seabirds where the proportion of species meeting targets for abundance had declined since the mid-2000s to 59% in 2014. The UK target was also not met in the Celtic Seas. Here, the proportion of species meeting targets for abundance in both breeding seabirds and non-breeding waterbirds had also declined since the mid-2000s to 63% and 53% respectively in 2015.

There were no clear differences in the assessments between the five functional groups within the non-breeding waterbirds that visit the North Sea and Celtic Seas coasts during migration or during winter. However, species of seabird that feed on fish within the water column have fared much better than those that feed at the surface. The availability of small forage fish species such as the sandeel and sprat at the surface is likely limiting the breeding success of some species such as the black-legged kittiwake. Drivers of food availability are likely to be ecosystem-specific changes, possibly initiated by past and present fisheries, in combination with climate change.

Further information

This assessment may reflect a continuation of a shift in the centre of abundance of waterbird populations from south-west to north-east, as reported in the Initial Assessment 2012 (HM Government, 2012). This shift is thought to be caused by warming seas (see a review of the evidence in Pearce-Higgins and others, 2013). In the past, severe winter weather increased the mortality of some species, but recent milder winters have increased survival rates. This has allowed more birds to take advantage of the richer feeding in the muddier east coast estuaries with a much-reduced risk of cold weather mortality. As a result, more birds are now wintering on the east coast of Britain, and fewer birds are wintering in the south-west. Such benefits may be countered in the future by the negative impacts of ‘coastal squeeze’ as rising sea levels lead to the loss of intertidal feeding areas. It is not clear whether birds will continue to move north-eastwards and relocate elsewhere in Europe, or if total numbers migrating through and wintering in Europe will decline because of these climate-related changes.

Knowledge gaps

The following two knowledge gaps are identified:

1. This indicator assessment method could also be applied to data on seabirds and waterbirds collected at sea. Extending the assessment of abundance of seabirds and waterbirds at sea may provide a more direct indicator of impacts from human activities. However, the temporal and spatial coverage of monitoring of seabirds and waterbirds at-sea in the UK would need to be improved to achieve this.

2. The baselines used in this indicator assessment were assigned to the beginning of the time series of data being assessed. It would be more objective to set baselines that include ‘reference levels,’ at which we would expect the population size to be if anthropogenic impacts were negligible.

Further information

Inclusion of at-sea data

Data on seabirds at sea, collected from boats or planes, were not included in the abundance indicator. However, these data could be included in the future to obtain reliable results on trends of species that occur in substantial numbers in the offshore regions. At present, several other Contracting Parties of OSPAR carry out or plan to carry out national at-sea monitoring programmes. In UK waters and elsewhere, there are either limited or no at-sea surveys. Those that do exist are sparse in spatial and temporal coverage. Overall, co-ordination of surveys, for example in timing, between countries is lacking There is a need to develop a concept for joint survey efforts providing the necessary data basis for the abundance indicator work, and also to implement this concept in the framework of national survey programmes in future years. It would be additionally helpful to develop a methodological approach for aggregating and analysing the data.

Baselines

The baselines for the relative breeding and non-breeding abundance of each species was equal to the abundance in the second year of the time series (1992). However, the UK initially proposed baseline values for seabird breeding abundance followed advice that it is preferable to set baselines objectively, by using one of the methods (1) or (2), listed below (ICES, 2015).

1. ‘Historical reference’ - where we know abundance at a point in the past long before the time -series began, but don’t know why it may have changed since. Use of historical population estimates as baselines if they were recorded: 
   • before known human impacts; or
   • before other major declines in population; or
   • at known plateaus in population trends, following increases and peaks in population size.
2. ‘Reference level’ - what we would expect the population size to be if anthropogenic impacts were negligible (this can be derived from known population sizes either historically or from within available time series). Use of the highest known population estimate when the population has decreased in size, because of human impacts such as. periods of severe contamination or following stochastic natural impacts like severe weather wrecks. Use of recent population estimates (for example, the (previous five-year mean) when a species has been colonising.

However, most other OSPAR Contracting Parties did not provide objective baselines, and hence this international assessment defaulted to baseline set at the start of the available time series. Future assessments would be more objective if international baselines could be set that followed the methods outlined above.

References

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Blew J, Günther K, Hälterlein B, Kleefstra R, Laursen K, Scheiffarth G (2016) ‘Trends of Migratory and Wintering Waterbirds in the Wadden Sea 1987/1988 - 2013/2014’ Wadden Sea Ecosystem No. 37. Common Wadden Sea Secretariat, Joint Monitoring Group of Migratory Birds in the Wadden Sea,Wilhelmshaven, Germany (viewed on 22 October 2018)

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ICES (2010) ‘Report of the Working Group on Seabird Ecology (WGSE)’ 15–19 March 2010, Copenhagen. ICES CM 2010/SSGEF:10. 81 pages (viewed on 22 October 2018)

ICES (2011) ‘Report of the Working Group on Seabird Ecology (WGSE)’ 1–4 November 2011, Madeira, Portugal. ICES CM 2011/SSGEF:07. 77 pages (viewed on 22 October 2018)

ICES (2012) ‘General advice on EcoQO for seabird populations in OSPAR regions II and III’ In: Report of the ICES Advisory Committee, 2012. ICES Advice 2012, Book 1, Section 1.5.5.1 (viewed on 22 October 2018)

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Acknowledgements

Assessment Metadata

Please contact marinestrategy@defra.gov.uk for metadata information

Recommended reference for this indicator assessment

Ian Mitchell,¹ Graham French,¹, Andrew Douse,² Simon Foster,² Melanie Kershaw,³ Neil McCulloch⁴, Matty Murphy⁵, & Jane Hawkridge¹ 2018. Marine Bird Abundance*. UK Marine Online Assessment Tool, available at: /biodiversity-food-webs-and-marine-protected-areas/birds/abundance/

* Adapted from OSPAR Intermediate Assessment 2017 on Marine Bird Abundance

¹Joint Nature Conservation Committee

²Scottish Natural Heritage

³Natural England

⁴Department of Environment, Agriculture & Rural Affairs, Northern Ireland

⁵Natural Resources Wales