C3: Diverse seas: status of marine mammals and marine birds

Short Description

This indicator of diverse seas tracks changes in status assessments of marine mammals and marine birds. The assessments of marine mammals will be based on trends in the abundance of harbour seals; grey seal pup production; and the abundance of cetaceans (whales and dolphins). The assessments of marine birds will be based on the proportion of marine birds that have met breeding or non-breeding abundance targets, which were set to inform progress towards Good Environmental Status (GES). The GES assessments of marine mammals and birds were used in the updated UK Marine Strategy Part One (2019) and to fulfil reporting commitments under the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).

Readiness and links to data

This indicator is not available for reporting in 2023 in a finalised form as some further development is required. An interim indicator is presented here that shows (a) changes in the abundance of harbour seals and the production of grey seal pups in the north-east and south-east of England, and (b) changes in the abundance of breeding and non-breeding marine birds in the Greater North Sea and Celtic Seas (OSPAR marine regions including data from neighbouring countries). The data for seals and marine birds used for this interim indicator have been reported via the OSPAR Quality Status Report 2023 (QSR) and at a UK scale under the updated UK Marine Strategy Part One (2019). The marine birds component of the indicator is based on the latest methodology developed for the OSPAR QSR. The latest OSPAR assessment for seals used data collected from across the UK from 1994 to 2019, whereas the interim indicator outputs presented here in Figures C3ai and C3aii also include the most recent data available, published as part of annual outputs by the Special Committee on Seals (SCOS).

Trends in the abundance and distribution of whale and dolphin species were assessed in the OSPAR QSR using data derived from dedicated aerial and shipboard surveys to generate estimates of abundance. However, for most species, trends in abundance could not be determined because there were an insufficient number of population estimates. Cetaceans are not yet included in the C3 indicator for this reason, however it is expected that new population estimates, generated as part of the 2022 Small Cetaceans in Atlantic Waters and the North Sea (SCANS) IV programme will enable further development.

At this time, the marine bird component of the indicator is only based on breeding and non-breeding abundance. Future assessments of marine birds will be based on the integration of OSPAR abundance and breeding productivity indicators following the approach applied for the forthcoming Marine Birds Thematic Assessment that will be reported for the OSPAR QSR 2023.

The indicator will be kept under review during the development of ‘D5 Conservation status of our native species’ as some elements of this indicator may ultimately be included in D5 instead.

Notes on indicator

Seal species were deemed to meet abundance targets under the OSPAR QSR 2023 if harbour seal abundance and grey seal pup production: a) declined by less than an average of 1% per year in the previous 6-year period, or b) decreased by less than 25% since the baseline year (1992 or start of time series, if later). The UK Marine Strategy Part One (2019) GES assessment for seals covered the Celtic Seas and Greater North Sea.

The term “marine bird” includes seabirds that spend the majority of their lives at sea (petrels and shearwaters, gannets and cormorants, skuas, gulls, terns and auks) and waterbirds that mostly inhabit intertidal areas or inshore areas close by (waders, ducks, geese, swans, grebes and divers). For most seabirds, and some waterbird species, abundance is assessed when they are breeding, because they are much easier to count when they aggregate on land to breed in colonies than when they are dispersed at sea over large areas. Most waterbirds, and some seabird species, are assessed using non-breeding abundance, because they are much easier to count when they aggregate in intertidal and inshore areas during migration or in winter. Assessments of marine birds are conducted separately for breeding and non-breeding birds as these often do not belong to the same population and because most species in the breeding assessment are seabirds that use the wider marine environment and most species in the non-breeding assessment use intertidal and inshore areas. The breeding and non-breeding assessments therefore indicate impacts from different suites of pressures, operating in different parts of the marine environment.

Marine birds are considered in good status if at least 75% of species assessed achieve targets for relative breeding or non-breeding abundance (dashed line on figures C3bi and C3bii). The relative abundance of a species is the annual abundance expressed as a proportion of the baseline, which was either based on a regression analysis of the first 10 years of data (1991 to 2000) with the predicted value for the first year (1991) used as the baseline value, or the mean of the first ten years. Species were deemed to meet abundance targets if their relative abundance was either: equal or above 80% of the baseline for species that lay one egg or equal or above 70% of the baseline for species that lay more than one egg.

Indicator components

Figure C3ai: Harbour seal abundance, north-east and south-east England, 1994 to 2021

Table C3ai: Harbour seal abundance, north-east and south-east England, 1994 to 2021

Year Northeast England Southeast England
1994 48.00 -
1995 46.00 2,793.00
1996 55.00 2,866.00
1997 54.00 3,223.00
1998 53.00 3,441.00
1999 48.00 3,557.00
2000 69.00 4,241.00
2001 69.00 4,404.00
2002 62.00 4,012.00
2003 48.00 3,361.00
2004 50.00 3,324.00
2005 67.00 3,312.00
2006 62.00 2,964.00
2007 50.00 3,177.00
2008 50.00 3,183.00
2009 58.00 3,952.00
2010 62.00 3,733.00
2011 66.00 3,946.00
2012 72.00 4,513.00
2013 83.00 4,504.00
2014 90.00 4,681.00
2015 91.00 4,740.00
2016 86.00 5,062.00
2017 87.00 4,965.00
2018 79.00 4,961.00
2019 79.00 3,752.00
2020 94.00 3,998.00
2021 89.00 3,505.00

Trend description for C3ai

In the south-east, where the majority of the England population is concentrated, numbers of harbour seals have increased from 2,793 in 1995 to 4,944 in 2018, followed by a sharp decline to 3,752 in 2019, corresponding to a reduction of 25%. Since 2019, numbers have continued to decline at a slower rate reaching a value of 3,505 in 2021. Smaller numbers of harbour seals are present in north-east England (mostly within the Teesmouth estuary). Here, the species has increased from 45 animals in 1994 to a high of 94 in 2020. In the latest year in the series (2021) this number has reduced to 89. The UK Marine Strategy Part One (2019) assessment based on the period 1994 to 2014 concluded that because of declines in Scotland, GES had not been achieved for harbour seal abundance in the UK Greater North Sea sub-region (which includes seal populations in the north-east and south-east of England). The more recent OSPAR QSR 2023 assessment for harbour seals based on the period 1992-2019 concluded that while long-term abundance has increased at sites along the east coast of England, in South-East England, the short-term (five year) assessment threshold of no decline at a rate greater than 1% per year has not been achieved.

Assessment of change

An increase (or improvement) in the abundance of harbour seals in both the north-east and south-east of England was observed in the medium and long-term. Increases were also found in the north-east over the short-term. A decrease (deterioration) in harbour seal abundance was found in south-east England over the short-term. In the north-east, numbers of harbour seals are much lower and small increases in population will correspond to high increases in percentage.

Change since 2018 has also been assessed. Since 2018, there was an increase in harbour seal abundance in the north-east, and a decrease in the south-east. However, this is based on only 4 data points so should be considered as indicative and not evidence of a clear trend.

Assessment results presented here are not directly comparable with analyses published elsewhere that use different methodologies to explore these indicators or are based on alternative datasets.

Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.

Table C3ai: Assessment of change

Component Subcomponent Period Date range Percentage change Assessment methodology Assessment of change
C3ai Southeast England Short term 2015 to 2020 -14.70 Loess Deterioration
C3ai Southeast England Medium term 2010 to 2020 3.87 Loess Improvement
C3ai Southeast England Long term 1995 to 2020 38.32 Loess Improvement
C3ai Northeast England Short term 2015 to 2020 8.08 Loess Improvement
C3ai Northeast England Medium term 2010 to 2020 34.96 Loess Improvement
C3ai Northeast England Long term 1994 to 2020 86.50 Loess Improvement

Note that assessment categories for the short, medium and long term were assigned based on smoothed data, so percent change figures in Table C3ai may differ from unsmoothed values quoted elsewhere. Percent change refers to the difference seen from the first to last year in the specified date range.

Figure C3aii: Atlantic grey seal pup production, north-east and south-east England, 1991 to 2019

Table C3aii: Atlantic grey seal pup production, north-east and south-east England, 1991 to 2019

Year Northeast England Southeast England
1991 927 227
1992 985 200
1993 1051 205
1994 1025 302
1995 1070 334
1996 1061 310
1997 1284 382
1998 1309 463
1999 843 503
2000 1171 618
2001 1247 659
2002 1200 811
2003 1266 940
2004 1133 1176
2005 1138 1276
2006 1254 1416
2007 1164 1659
2008 1318 1953
2009 1346 2268
2010 1498 2608
2011 1555 2911
2012 1603 3385
2013 1575 4018
2014 1740 5055
2015 1876 5500
2016 2295 5918
2017 2131 6558
2018 2737 7147
2019 2823 7902

Trend description for C3aii

In south-east England, grey seal pup production has increased exponentially from 200 pups in 1992 to 7,902 pups in 2019. In north-east England, the rise in pup production has been more gradual, from 985 pups in 1992 to 2,823 in 2019. The UK Marine Strategy Part One (2019) assessment based on the period 1992 to 2014 concluded that GES for both grey seal abundance, and grey seal pup production has been achieved in the Greater North Sea. The OSPAR QSR 2023 assessment based on the reporting period 1992-2019 concluded that grey seal pup production within the Greater North Sea is largely increasing or remained stable. Both in north-east and south-east England, pup production is achieving thresholds.

Assessment of change

An increase (or improvement) in grey seal pup production was found in both regions over most recent 5 years for which trends can be assessed (2013 to 2018), as well as over the medium and long-term. These overall trends were assessed using smoothed data do not pick up on small scale patterns in abundance.

Change since 2018 has also been assessed. An increase in grey seal pup production was found in both regions. However, this is based on 2 years of data so should be considered as indicative and not evidence of a clear trend.

Assessment results presented here are not directly comparable with analyses published elsewhere that use different methodologies to explore these indicators or are based on alternative datasets.

Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.

Table C3aii: Assessment of change

Component Subcomponent Period Date range Percentage change Smoothing function Assessment of change
C3aii Northeast England Short term 2013 to 2018 50.98 Loess Improvement
C3aii Northeast England Medium term 2008 to 2018 98.34 Loess Improvement
C3aii Northeast England Long term 1991 to 2018 170.54 Loess Improvement
C3aii Southeast England Short term 2013 to 2018 77.45 Loess Improvement
C3aii Southeast England Medium term 2008 to 2018 276.42 Loess Improvement
C3aii Southeast England Long term 1991 to 2018 2,931.89 Loess Improvement

Note that assessment categories for the short, medium and long term were assigned based on smoothed data, so percent change figures in Table C3aii may differ from unsmoothed values quoted elsewhere. Percent change refers to the difference seen from the first to last year in the specified date range.

Figure C3bi: Change in the annual proportion of marine bird species achieving relative breeding abundance targets, Greater North Sea and Celtic Seas, 1996 to 2019

Table C3bi: Change in the annual proportion of marine bird species achieving relative breeding abundance targets, Greater North Sea and Celtic Seas, 1996 to 2019

Year Celtic Seas Greater North Sea Threshold Value
1996 100.00 100.00 75.00
1997 100.00 100.00 75.00
1998 100.00 100.00 75.00
1999 100.00 100.00 75.00
2000 100.00 96.43 75.00
2001 94.44 82.14 75.00
2002 94.44 78.57 75.00
2003 94.44 78.57 75.00
2004 88.89 71.43 75.00
2005 88.89 71.43 75.00
2006 77.78 71.43 75.00
2007 77.78 64.29 75.00
2008 72.22 57.14 75.00
2009 72.22 57.14 75.00
2010 72.22 57.14 75.00
2011 72.22 57.14 75.00
2012 72.22 57.14 75.00
2013 72.22 53.57 75.00
2014 66.67 53.57 75.00
2015 55.56 53.57 75.00
2016 55.56 50.00 75.00
2017 61.11 50.00 75.00
2018 72.22 - 75.00
2019 72.22 - 75.00

Trend description for C3bi

The proportion of marine bird species meeting targets for breeding abundance in the Greater North Sea and Celtic Seas has remained below the 75% threshold since 2004 and 2008, respectively. In the Celtic Seas, the proportion has been 72.2% for the latest two years in the series (2018 and 2019), recovering to this level after a reduction to low of 55.6% in both 2015 and 2016. In the Greater North Sea, the proportion of species achieving abundance targets has reduced steadily since the start of the series to 50% in 2016 and 2017.

Assessment of change

In the Celtic seas, an increase (or improvement) in the breeding abundance of marine birds in the was observed in the long-term. However, there has been little to no change in breeding abundance in the medium term and an increase (improvement) was observed in the short-term. In the Greater North sea, decreases were observed over the long, medium and short-term assessment periods.

Change since 2018 has also been assessed in the Celtic Seas. Since 2018, there was little to no change in the breeding abundance of marine birds. However, this is based on 2 years of data so should be considered as indicative and not evidence of a clear trend.

Assessment results presented here are not directly comparable with analyses published elsewhere that use different methodologies to explore these indicators or are based on alternative datasets.

Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results pages.

Table C3bi: Assessment of change

Component Subcomponent Period Date range Percentage change Assessment methodology Assessment of change
C3bi Celtic Seas Short term 2014 to 2019 8.33 Rolling average Improvement
C3bi Celtic Seas Medium term 2009 to 2019 0.00 Rolling average Little or no change
C3bi Celtic Seas Long term 1996 to 2019 -27.78 Rolling average Deterioration
C3bi Greater North Sea Short term 2012 to 2017 -12.50 Rolling average Deterioration
C3bi Greater North Sea Medium term 2007 to 2017 -22.22 Rolling average Deterioration
C3bi Greater North Sea Long term 1996 to 2017 -50.00 Rolling average Deterioration

Percent change refers to the difference seen from the first to last datapoint in the specified date range.

Figure C3bii: Change in the annual proportion of marine bird species achieving relative non-breeding abundance targets, Greater North Sea and Celtic Seas, 1996 to 2020

Table C3bii: Change in the annual proportion of marine bird species achieving relative non-breeding abundance targets, Greater North Sea and Celtic Seas, 1996 to 2020

Year Celtic Seas Greater North Sea Threshold Value
1996 100.00 97.56 75.00
1997 100.00 100.00 75.00
1998 100.00 100.00 75.00
1999 100.00 97.56 75.00
2000 96.30 92.68 75.00
2001 96.30 95.12 75.00
2002 92.59 92.68 75.00
2003 92.59 92.68 75.00
2004 92.59 90.24 75.00
2005 88.89 87.80 75.00
2006 85.19 82.93 75.00
2007 81.48 80.49 75.00
2008 74.07 80.49 75.00
2009 74.07 78.05 75.00
2010 74.07 78.05 75.00
2011 74.07 73.17 75.00
2012 77.78 75.61 75.00
2013 74.07 68.29 75.00
2014 59.26 70.73 75.00
2015 59.26 73.17 75.00
2016 51.85 68.29 75.00
2017 51.85 - 75.00
2018 51.85 - 75.00
2019 44.44 - 75.00
2020 48.15 - 75.00

Trend description for C3bii

The proportion of marine bird species meeting targets for non-breeding abundance in the Greater North Sea has seen an overall decline since the start of the series to 68% in 2017, with the threshold of 75% not being met since 2012. The proportion of marine bird species meeting targets for non-breeding abundance in the Celtic Seas has also declined sharply since the start of the time series to a value of 48.1% in 2020, remaining below the 75% threshold in every year since 2012.

Assessment of change

In the assessment of non-breeding abundance of marine birds, a decrease, or deterioration was observed in the long-term, medium-term and the short-term in both regional seas: the Celtic Seas and the Greater North Sea.

Change since 2018 has also been assessed in the Celtic Seas. Since 2018, there was a decrease (a deterioration) in the non-breeding abundance of marine birds. However, this is based on 3 years of data so should be considered as indicative and not evidence of a clear trend.

Assessment results presented here are not directly comparable with analyses published elsewhere that use different methodologies to explore these indicators or are based on alternative datasets.

Further information on this assessment, along with details on the methodology, is provided in the Assessment background page. Summaries by 25 Year Environment Plan goal and information on indicator links are presented in the Assessment results.

Table C3bii: Assessment of change

Component Subcomponent Period Date range Percentage change Assessment methodology Assessment of change
C3bii Celtic Seas Short term 2015 to 2020 -18.75 Rolling average Deterioration
C3bii Celtic Seas Medium term 2010 to 2020 -35.00 Rolling average Deterioration
C3bii Celtic Seas Long term 1996 to 2020 -51.85 Rolling average Deterioration
C3bii Greater North Sea Short term 2011 to 2016 -6.67 Rolling average Deterioration
C3bii Greater North Sea Medium term 2006 to 2016 -17.65 Rolling average Deterioration
C3bii Greater North Sea Long term 1996 to 2016 -30.00 Rolling average Deterioration

Percent change refers to the difference seen from the first to last datapoint in the specified date range.

Indicator Metadata