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 (UKMS) Part One (2019) and to fulfil reporting commitments under the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).
As of the 2025 update of this indicator, components C3ai and C3aii (looking at trends in the abundance of harbour seals and grey seal pup production respectively) have been temporarily removed as part of an ongoing data audit and review of the methodology used to produce them. We intend to reinstate the components once the review is complete and sufficient refinements have been made.
Readiness and links to data
An interim indicator is presented here that shows 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 marine birds used for this interim indicator have been reported via the OSPAR Quality Status Report 2023 (QSR). The marine birds component of the indicator is based on the latest methodology developed for the OSPAR QSR.
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 to the Marine Birds Thematic Assessment reported for the OSPAR QSR 2023. A Marine Mammals Thematic Assessment is also available.
Notes on indicator
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 10 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 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 |
|---|---|---|
| 1996 | 100.00 | 100.00 |
| 1997 | 100.00 | 100.00 |
| 1998 | 100.00 | 100.00 |
| 1999 | 100.00 | 100.00 |
| 2000 | 100.00 | 96.43 |
| 2001 | 94.44 | 82.14 |
| 2002 | 94.44 | 78.57 |
| 2003 | 94.44 | 78.57 |
| 2004 | 88.89 | 71.43 |
| 2005 | 88.89 | 71.43 |
| 2006 | 77.78 | 71.43 |
| 2007 | 77.78 | 64.29 |
| 2008 | 72.22 | 57.14 |
| 2009 | 72.22 | 57.14 |
| 2010 | 72.22 | 57.14 |
| 2011 | 72.22 | 57.14 |
| 2012 | 72.22 | 57.14 |
| 2013 | 72.22 | 53.57 |
| 2014 | 66.67 | 53.57 |
| 2015 | 55.56 | 53.57 |
| 2016 | 55.56 | 50.00 |
| 2017 | 61.11 | 50.00 |
| 2018 | 72.22 | - |
| 2019 | 72.22 | - |
Trend description for C3bi
The proportion of marine bird species meeting targets for breeding abundance in the Greater North Sea and Celtic Seas has generally remained below the 75% threshold since 2011 and 2008, respectively. In the Celtic Seas, the proportion has been 72.2% for the latest 2 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 |
Percentage 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 |
|---|---|---|
| 1996 | 100.00 | 97.56 |
| 1997 | 100.00 | 100.00 |
| 1998 | 100.00 | 100.00 |
| 1999 | 100.00 | 97.56 |
| 2000 | 96.30 | 92.68 |
| 2001 | 96.30 | 95.12 |
| 2002 | 92.59 | 92.68 |
| 2003 | 92.59 | 92.68 |
| 2004 | 92.59 | 90.24 |
| 2005 | 88.89 | 87.80 |
| 2006 | 85.19 | 82.93 |
| 2007 | 81.48 | 80.49 |
| 2008 | 74.07 | 80.49 |
| 2009 | 74.07 | 78.05 |
| 2010 | 74.07 | 78.05 |
| 2011 | 74.07 | 73.17 |
| 2012 | 77.78 | 75.61 |
| 2013 | 74.07 | 68.29 |
| 2014 | 59.26 | 70.73 |
| 2015 | 59.26 | 73.17 |
| 2016 | 51.85 | 68.29 |
| 2017 | 51.85 | - |
| 2018 | 51.85 | - |
| 2019 | 44.44 | - |
| 2020 | 48.15 | - |
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 2016, 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% 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, medium 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 |
Percentage change refers to the difference seen from the first to last datapoint in the specified date range.