Assessment of progress towards the achievement of Good Environmental Status for marine bird biodiversity.

Extent to which Good Environmental Status has been achieved

The UK has achieved its aim of Good Environmental Status for non-breeding waterbirds in the Greater North Sea but not in the Celtic Seas. Breeding seabirds have not achieved Good Environmental Status.

How progress has been assessed

In the UK Marine Strategy Part One, the UK set out the following ‘Characteristics of Good Environmental Status(HM Government, 2012):

“At the scale of the Marine Strategy Framework Directive sub-regions, and in line with prevailing conditions, the loss of biodiversity has been halted and where practicable, restoration is underway:

  • The abundance, distribution, extent, and condition of species and habitats in UK waters are in line with prevailing environmental conditions as defined by specific targets for species and habitats.
  • Marine ecosystems and their constituent species and habitats are not significantly impacted by human activities such that the specific structures and functions for their long-term maintenance exist for the foreseeable future.
  • Habitats and species identified as requiring protection under existing national or international agreements are conserved effectively through appropriate national or regional mechanisms.”

The progress towards achievement of Good Environmental Status for biodiversity was assessed separately for two groups of birds:

  1. Breeding seabirds: species that are monitored on land during the breeding season.
  2. Non-breeding waterbirds: species that are monitored outside of the breeding season while they are migrating or overwintering around the coast.

The division of non-breeding waterbirds and breeding seabirds makes ecological sense: the assessment of non-breeding waterbirds can potentially indicate human impacts in intertidal and subtidal areas while the assessment of breeding seabirds indicates human impacts in the wider marine environment. The status of both breeding seabirds and non-breeding seabirds would need to be consistent with the achievement of Good Environmental Status, for Good Environmental Status to be achieved for marine bird biodiversity.

The extent that Good Environmental Status, as articulated in the criteria for biodiversity in the Commission Decision 2010/447/EU (European Commission, 2010), had been achieved, was assessed using targets set out for marine birds in the UK Marine Strategy Part One (HM Government, 2012).The status of non-breeding waterbirds was assessed against a single target for population size. A second target for the species distribution of marine birds was also included in the UK Marine Strategy, and a corresponding indicator developed and assessed for non-breeding seabirds. However, the ability of this indicator to detect biologically meaningful changes in distribution of marine birds is unclear and further development is therefore required before it could be included in an integrated assessment of Good Environmental Status. The status of breeding seabirds was assessed against two targets, one for population size and one for population condition. Indicators relevant to the targets were agreed, some in co-operation with OSPAR, which used data collected by monitoring programmes in the UK and by neighbouring countries on the Celtic Seas and the Greater North Sea. Integrating the results of these indicator assessments has enabled us to evaluate the extent that these targets have been met, and a further integration of the target evaluations has enabled us to provide the overall assessment of what progress has been made since the Initial Assessment 2012 (HM Government, 2012), towards achieving Good Environmental Status for biodiversity (Figure 1).

Schematic showing how indicators and targets integrated to assess progress towards Good Environmental Status for marine birds in the Greater North Sea (top) and Celtic Seas (bottom).Figure 1. Schematic showing how indicators and targets integrated to assess progress towards Good Environmental Status for marine birds in the Greater North Sea (top) and Celtic Seas (bottom).

Progress since 2012

In the Greater North Sea, the proportion of waterbird species meeting thresholds for non-breeding abundance has declined sharply but is still on target. The proportion of seabird species meeting thresholds for breeding abundance has remained stable but below target. More seabird species are now experiencing frequent, widespread breeding failure.

In the Celtic Seas, the proportion of waterbird species meeting thresholds for non-breeding abundance has declined sharply. The proportion of seabird species meeting thresholds for breeding abundance has remained stable but below target. More seabird species are now experiencing frequent widespread breeding failure.

New measures include designation of marine Special Protection Areas offshore, and black guillemot Marine Protected Areas in Scotland.

Outstanding issues

Reduced availability of small fish, on which the seabirds feed, has been largely responsible for declines in seabird breeding abundance and the frequent, widespread breeding failures in some species. There is a lack of understanding of how climate change is driving shifts in the food web that have led to these reductions in food availability. The decline in wintering waterbird abundance in the Celtic Seas is thought to be part of a north-east shift in their distribution in response to milder winters. Climate change is thought to be driving these shifts, but the role of additional human impact is unclear.

Achievement of targets and indicators used to assess progress

Photographic credits: Abundance © Graeme Duncan. Breeding success/failure © Matt Parsons. Distribution © JNCC. Invasive mammals © Phil Davison. Kittiwake breeding success © Ian Mitchell.

Table 1. Summary of targets, indicators, and assessment results.

Target

Assessment result

Bird group status

Greater North Sea

Celtic Seas

Population size: Changes in abundance of marine birds should be within individual target levels in 75% of species monitored.

Target met in 78% of non-breeding waterbird species

Target met in only 53% of non-breeding waterbird species

Non-breeding waterbird status appears not to be consistent with Good Environmental Status.

Target met in only 59% of breeding seabird species

Target met in only 63% of breeding seabird species

Breeding seabird status appears not to be consistent with Good Environmental Status.

Population Condition: Widespread seabird colony breeding failures should occur rarely

Target not met: 35% of species experienced frequent, widespread breeding failures between 2010 and 2015

Target considered met: 75% of species did not experience frequent, widespread breeding failures between 2010 and 2015

Population Condition: The annual breeding success of black-legged kittiwakes should be in line with prevailing climatic conditions.

The target was met at kittiwake colonies on the UK mainland coast of the North Sea, but no colonies passed the assessment in Shetland and Orkney, where the population is in steep decline.

The target was not assessed in the Celtic Seas because we were unable to take prevailing climatic conditions into account and to thus distinguish impacts from human activities.

Population Condition: The risks to island seabird colonies from non-native mammals are reduced.

The UK target could not be assessed because there has been no previous assessment of this risk. But the risk from invasive predatory mammals has been minimised by effective biosecurity at only 3 out of 21 and nine protected sites assessed in the Greater North Sea and Celtic Seas, respectively.

Further information

Assessment of progress towards the achievement of Good Environmental Status for non-breeding waterbirds

The assessment of non-breeding waterbirds was based on progress towards a single target (HM Government, 2012):

Population Size: “At the scale of the Marine Strategy Framework Directive sub-regions 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.

This target was met for non-breeding waterbirds in the Greater North Sea but not in the Celtic Seas. In the Greater North Sea, an abundance of more than 75% of species assessed was sufficiently close to or above the baseline set in 1992. In the Celtic Seas, the proportion of species meeting targets for abundance declined since the mid-2000s to 53% in 2015. The assessment was unable to distinguish human impacts from the effects of prevailing environmental conditions. Milder winters are thought to be allowing waterbirds to move away from Celtic Seas coasts, to spend the winter foraging in the larger estuaries and more extensive intertidal areas in the Greater North Sea.

Evidence to support the evaluation of non-breeding waterbirds

The supporting evidence for this target evaluation and the extent that criterion the corresponding criteria for Good Environmental Status (European Commission 2010; 2017) have been achieved comes from the assessment of the marine bird abundance indicator. This indicator assessment has been undertaken as part of the OSPAR Intermediate Assessment (OSPAR Commission, 2017). As such, the indicator assessment was undertaken in each OSPAR Region (approximately corresponding to each Marine Strategy Framework Directive sub-region) using data from the UK and neighbouring countries. The UK assessment included species of waterbirds such as wildfowl and waders that regularly occur in the UK. Indicators of the abundance of each species in each sub-region were constructed from trends in numbers of birds using intertidal and inshore areas during migration or over-winter (46 species in the North Sea and 40 species in Celtic Seas). The ‘target levels’ for each species, as referred to in the UK target, are achieved if annual relative abundance (defined as the ratio of annual abundance to a chosen baseline abundance, here that of 1992 – the second year of the timeseries) is greater than 0.8 for species that lay one egg, or 0.7 for species that lay more than one egg, which reflects the resilience of different species to declines in their populations.

The UK target for population size was met for 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 Celtic Seas. Here, the proportion of species meeting targets for abundance in non-breeding waterbirds had declined since the mid-2000s to 53% in 2015. The non-breeding waterbirds that visit the North Sea and Celtic Seas coasts during migration and/or during winter are from all 5 marine bird functional groups (wading feeders, grazers, surface feeders, water column feeders or ‘divers’, and benthic feeders), with the majority being wading feeders. There were no clear differences in the assessments between these groups, except that a lower proportion of benthic feeding species of duck in the North Sea had met targets compared to the other groups.

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. 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 elsewhere in the North Sea, and fewer birds are wintering in the south-west of Britain.

Assessment of progress towards the achievement of Good Environmental Status for breeding seabirds

In both the Greater North Sea and Celtic Seas, breeding seabirds are not considered to be in Good Environmental Status. In more than a third of species, breeding abundance is 20-30% lower than in the 1990s. There have been frequent, widespread breeding failures in recent years in a third of species in the North Sea and a quarter of species in the Celtic Seas. Lower availability of small fish, on which the seabirds feed, has been largely responsible. Climate change is likely to be driving these reductions in food availability, but potential impacts from human-related activities cannot be ruled out. The assessment of breeding seabirds was based on progress towards two targets (HM Government, 2012):

  1. Population Size: At the scale of the Marine Strategy Framework Directive sub-regions 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 the species monitored.
  2. Population Condition: At the scale of the Marine Strategy Framework Directive sub-regions marine bird productivity is not significantly affected by human activities: annual breeding success of black-legged kittiwakes should not be significantly different, statistically, from levels expected under prevailing climatic conditions such as sea surface temperature); and widespread seabird colony breeding failures should rarely occur in other species that are sensitive to changes in food availability; and the risks to island seabird colonies from non-native mammals are reduced.

Assessment of the extent that the target for population size of breeding seabirds has been met

The UK target for population size was not met for breeding seabirds in both the Greater North Sea and the Celtic Seas.

Evidence to support the evaluation of the extent that the target for population size has been achieved for breeding seabirds

The supporting evidence for this target evaluation and the extent that criterion the corresponding criteria for Good Environmental Status (European Commission 2010; 2017) have been achieved comes from the assessment of the marine bird abundance indicator.

This indicator assessment has been undertaken as part of the OSPAR Intermediate Assessment (OSPAR Commission, 2017). As such, the indicator assessment was undertaken in each OSPAR Region (approximate to each Marine Strategy Framework Directive sub-region) using data from the UK and neighbouring countries. The UK assessment included species of seabirds that regularly breed in the UK. Indicators of the abundance of each species in each sub-region were constructed from trends in numbers of seabirds at specific breeding colonies, such as puffins, guillemots, gulls, and terns (22 species in the North Sea and 19 species in Celtic Seas). The ‘target levels’ for each species, as referred to in the UK target, are achieved if annual relative abundance (defined as the ratio of annual abundance to a chosen baseline abundance, here that of 1992 – the second year of the timeseries) is greater than 0.8 for species that lay one egg or 0.7 for species that lay more than one egg, which reflects the resilience of different species to declines in their populations. The UK target for population size was not met for breeding seabirds in both sub-regions, the proportion of breeding seabird species which meet targets for abundance had declined since the mid-2000s to 59% in the North Sea in 2014 and 63% in the Celtic Seas in 2015.

The breeding seabirds in this assessment forage offshore, mostly on fish. The species that feed on fish within the water column are faring much better than those that feed at the surface in that a higher proportion were meeting targets for abundance. This agrees with the results of the indicator on marine bird breeding success/failure: the availability of small forage fish species such as sandeel and sprat at the surface is probably limiting the breeding success of species like black-legged kittiwake. Ecosystem-specific changes are likely to determine food availability, possibly initiated by past and present fisheries, in combination with climate change.

Assessment of the extent that the target for population condition of breeding seabirds has been met

The UK target for population condition was not met for breeding seabirds in the Greater North Sea: 35% of species experienced frequent, widespread breeding failures between 2010 and 2015. The species that frequently failed to raise young all feed and rely on small fish in the surface layers of the sea. The breeding success of one such species, the black-legged kittiwake was in line with prevailing climatic conditions (in this case, sea surface temperature) at colonies on the UK mainland coast of the North Sea, however, prevailing conditions did not explain the steep population decline in Shetland and Orkney, where no colonies passed the assessment. The reasons for the poor breeding success in the Northern Isles are unclear.

The UK target for population condition was met for breeding seabirds in the Celtic Seas. 25% of species experienced frequent, widespread breeding failures between 2010 and 2015. But given the uncertainty around the main causes of breeding failure, it may be reasonable to expect frequent, widespread breeding failure to occur in 25% or fewer species and still achieve the UK target for population condition.

The UK target of a reduction in the risks to island seabird colonies from invasive predatory mammals could not be assessed because there has been no previous assessment of this risk. A total of 30 Special Protection Areas in the UK did not have invasive non-native and native predatory mammals on islands, protected for their breeding seabirds. But the risk from invasive predatory mammals has been minimised by effective biosecurity at only 3 out of 9 sites in the Greater North Sea and at only 3 out of 21 sites in the Celtic Seas. A further 12 Special Protection Areas had rats or feral cats present on islands and did not have effective biosecurity measures.

Evidence to support the evaluation of the extent that the target for population condition has been achieved for breeding seabirds

The supporting evidence for this target evaluation and the extent that criterion the corresponding criteria for Good Environmental Status (European Commission 2010; 2017) have been achieved comes from the assessment of three indicators:

  1. Marine bird breeding success/failure (OSPAR Common Indicator)
  2. Kittiwake breeding success
  3. Invasive mammal presence on island seabird colonies

The assessment of the indicator on marine bird breeding success/failure was undertaken as part of the OSPAR Intermediate Assessment (OSPAR Commission, 2017). As such, the indicator assessment was undertaken in each OSPAR Region (approximate to each Marine Strategy Framework Directive sub-region) using data from the UK and neighbouring countries. The UK assessment included species of seabirds that regularly breed in the UK.

Indicators of breeding failure were constructed using time series of annual mean breeding success (number of chicks fledged per pair). In this context, ‘breeding failure’ is defined when almost no chicks (0.1 or fewer chicks per pair) are produced at a seabird colony in a year. ‘Widespread’ breeding failure occurred if the percentage of colonies failing per year was more than 5% (or, for tern species, the mean percentage of colonies failing over the preceding 15 years). Widespread failure was considered to occur ‘frequently’ if it occurred in more than 3 years out of 6, during the assessment period 2010 to 2015. It is of potential conservation concern if any species of seabird is experiencing frequent, widespread colony failure. But given the uncertainty around the main causes of breeding failure, it may be reasonable to expect frequent, widespread breeding failure to occur in 25% or fewer species and still achieve the UK target.

The UK target for breeding success/failure was met in 75% of species in the Celtic Seas, but not in the Greater North Sea, where 35% of species experienced frequent, widespread breeding failures between 2010 and 2015. In both sub-regions, the species that frequently failed to raise young, typically gulls and terns, all feed on small fish at the surface. Species that dive below the surface in pursuit of fish showed widespread breeding failures much less frequently. This suggests that it is not a shear abundance of prey that is affecting their productivity and breeding numbers, but the availability of the prey to predators confined to the surface.

For one surface-feeding species, the kittiwake, which is one of the most-studied seabirds in the UK, there is only weak evidence linking prey abundance to kittiwake breeding success. The poor breeding success of kittiwakes has been related to increases in sea surface temperature and stratification within the water column, suggesting these environmental factors are important in determining the abundance and/or the availability of sandeels to kittiwakes and other surface-feeders. There is also evidence to suggest an additional negative impact of industrial sandeel fishing on the breeding success of kittiwakes at nearby colonies.

The indicator on kittiwake breeding success incorporates sea surface temperature data to distinguish between the effects of prevailing climatic conditions from those that may have resulted from human activities, such as fishing. The UK target for kittiwake breeding success was met for 9 out of a sample of 10 colonies on the UK mainland coast of the North Sea during the period 2010 to 2015, where breeding success of kittiwakes was in line with prevailing climatic conditions in at least 5 years out of 6. But in Shetland and Orkney, all 12 colonies assessed failed to meet the UK target during the period 2010 to 2015 and have failed to do so since the period 2001 to 2006. On the mainland North Sea coast, breeding success has recovered since 2000 when sandeel fishing that operated in eastern Scotland during the 1990s was banned. It is unclear what has produced the poorer than expected levels of breeding success in Orkney and Shetland. It is unlikely to have been due to fishing pressure because no sandeels were landed in Shetland during the period 2004 to 2015 and no sandeel fishery exists around Orkney. Natural factors such as predation from great skuas are likely to be the cause of poor breeding success at some colonies. Changes in ocean currents may have also led to low levels of sandeels in waters around Shetland. The indicator was also constructed using data from the Celtic Seas but there were no clear relationships between kittiwake breeding success and sea surface temperature at most of the colonies studied. Therefore, the target was not assessed in the Celtic Seas because we were unable to take prevailing climatic conditions into account and distinguish impacts from human activities.

Surface-feeding seabirds, in particular, fulmars, ingest floating plastic particles, which is expected to probably have a negative effect on their health, however the impact of plastic pollution on seabird populations is currently unknown.

The reduction of other pressures on seabirds through active management at colonies in the UK will help to enhance the resilience of the UK’s breeding seabirds to the impacts of climate change on their natural food supply. One such pressure comes from invasive predatory mammals, which can reduce seabird breeding numbers and breeding success and can lead to the desertion of whole colonies. This presents a significant risk to many important colonies around the UK. The assessment of the indicator on invasive mammal presence on island seabird colonies was the first such assessment, so could not be used to assess the UK target on reduction of risk from invasive predatory mammals. However, the assessment was able to determine if the risk has been minimised by existing biosecurity measures.

The assessment found that out of a total of 42 Special Protection Areas, designated for their island seabird colonies, 30 had no invasive predatory mammals. However, 14 of these sites had no biosecurity measures. The risk from invasive predatory mammals has been minimised by effective biosecurity at only 3 out of 9 sites in the Greater North Sea and at only 3 out of 21 sites in the Celtic Seas. Twelve out of the 42 seabird island Special Protection Areas had rats or feral cats and did not have effective biosecurity measures.

Moving forward

Further develop our understanding of the impacts of human pressures on marine birds.

References

Acknowledgements

European Commission (2010) ‘Commission Decision of 1 September 2010 on criteria and methodological standards on Good Environmental Status of marine waters’ (notified under document C (2010) 5956) (Text with EEA Relevance) (2010/477/EU). Official Journal of the European Union L232, 2.9.2010, pages 14-24 (viewed on 5 July 2018)

European Commission (2017) ‘Laying down criteria and methodological standards on good environmental status of marine waters and specifications and standardised methods for monitoring and assessment’ Commission Decision (EU) 2017/848 of 17 May 2017, repealing Decision 2010/477/EU Official Journal of the European Union L 125, 18.5.2017, pages 43-74 (viewed on 5 July 2018)

HM Government (2012) ‘Marine Strategy Part One: UK Initial Assessment and Good Environmental Status’ (viewed on 5 July 2018)

HM Government (2015) ‘Marine Strategy Part Three: UK Programme of Measures’ December 2015. (viewed on 5 July 2018)

OSPAR Commission (2017) ‘Intermediate Assessment 2017’ (viewed on 21 September 2018)