Skip to Content

Northern gannet (Morus bassanus)

The following has been adapted from original text by Sarah Wanless and Mike P. Harris in Seabird Populations of Britain and Ireland (with permission from A&C Black, London).

 

The northern gannet is the largest seabird in the North Atlantic. Gannets often perform dramatic plunge dives from high in the sky to catch fish up to depths of 20m and can stay submerged for over half a minute. They also feed from the surface on small shoaling fish like sandeels and on discards from fishing vessels, where their large size helps them out-compete most other scavenging species. The northern gannet is endemic to the North Atlantic and most breed in Britain and Ireland. There are 21 gannetries around Britain and Ireland, with most being on remote offshore islands and stacks, and two on mainland cliffs. Some colonies have been occupied for centuries and are large and conspicuous.

Conservation status

Northern gannet is currently identified as a conservation priority in the following:

Top

International importance

UK Population

Biogeographic Population

% World Population

293,200 AON*

418,441

55.6

* AON = Apparently Occupied Nests

 

The UK population figure (rounded to the nearest hundred), Biogeographic and World population figures were derived from data in Murray, S., Harris, M.P. and Wanless, S. 2015. The status of the gannet in Scotland in 2013-14. Scottish Birds 35: 3-18. However, figures were updated according to the latest Bempton Cliffs (Humberside) and Grassholm (Dyfed) counts in 2015, taking into account an increase of 1,151 AOS.

Top

UK population estimates and change 1969–2013/14 (census data)

There is a long tradition of counting northern gannets and the world population has been censused several times since the early 1900s, revealing a remarkably consistent increase of 2.0% per annum. While many of the smaller gannetries are surveyed annually, the larger colonies on remote offshore islands can only be censused by aerial survey which is a formidable undertaking. A complete census was carried out in 1994/95 and therefore full coverage of the species was not a top priority for Seabird 2000. Further censuses were conducted in 2004/05 and 2013-15.

 

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1984-85)

Gannet Census

(2003-04)

Gannet Census

(2013-15)

UK Population estimate (AON/AOS*)

113,006

157,247

218,546

293,161

% change since previous census   

n/a

+39

+39

+34**

*AON/AOS = Apparently Occupied Nests/Sites

**change between census in 2003-04 and colonies surveyed in 2013-14 and 2015.

For census results for individual countries and Ireland, the Channel Islands and the Isle of Man see under relevant sections below.

Top

Distribution/abundance

The Seabird 2000 census provides the most comprehensive recent assessment of the distribution and abundance of breeding seabirds. Numbers of Northern gannet found in different regions, and a map showing the location and size of colonies, is provided in the Seabird 2000 Northern gannet results page.

The locations sampled during the annual Seabird Monitoring Programme provide some information on distribution and are accessible via the Seabird Monitoring Programme online database.

Top

Annual abundance and productivity by geographical area

With reference to the regional accounts below please note the following:

Breeding abundance: graphs of abundance index with 95% confidence limits are only shown for a region where the trend produced has been deemed accurate (see methods of analysis). Where a trend was thought to be inaccurate, graphs of abundance at major colonies in a region may be shown instead, particularly if such colonies hold greater than 10% of the regional population, are monitored frequently and may thus help illustrate regional population fluctuations outwith national censuses. Occasionally, too few data have been collected regionally to produce either of these.

Productivity: graphs of productivity are only shown if analysis of breeding success data produced a significant result for regional and/or year effects (again see methods of analysis). If results were not significant, then a regional mean productivity value is given. However, on some occasions, too few data are available from which to provide a meaningful average. Furthermore, for 11 species where the quality of monitoring data available was considered high, population viability analysis was undertaken at the UK level and the results of this are also reported.

 

United Kingdom

Breeding abundance

northern-gannet-uk-ab.jpg

Figure 1. Trend in UK abundance index of northern gannet 1986–2018.


Given the logistical problems of surveying gannet colonies, annual sampling of all but the smaller colonies is impractical. The few colonies counted annually tend to be the smaller and increase at a greater rate than larger colonies (see Table 1), leading to bias in any estimated trends. Instead, decadal censuses have been undertaken since the 1980s1,2,3. The last census to cover all UK gannetries was carried out over two breeding seasons in 2003 and 20044. Figure 1 shows interpolated and extrapolated values from these complete censuses, expressed as an index. Over the long-term, the UK gannet population increased from 113,000 pairs in 1969/70 to 175,000 in 1984/85 to 218,000 AON in 2003/04 and reached 293,161 AON between 2013–2015.

In 2013 and 2014 all Scottish colonies were surveyed5, 6, 7, 8, while Bempton Cliffs (England) and Grassholm (Wales) were counted in 2015 (Table 1). Most have continued to increase, except the gannetries at Sule Stack and Scar Rocks, and new gannetries continue to be formed (Berneray, Western Isles) or re-colonised (Rockall, Western Isles). Since the 2013-15 gannet census, a few colonies have been surveyed again resulting in an additional 2,117 AOS (the dominant survey unit). Most colonies recorded an increase, however, at Troup Head numbers reduced from 6,456 AOS in 2014 to 3,847 AOS in 2016.

 

Table 1. Recent counts at UK gannetries compared to counts during the 2003-04 census (all data are of AON/AOS).

Area

Colony

2003-04 Census

Count (Year)

Change (%)

per annum

Shetland

Hermaness

15,633

25,580 2014

+64

+4.6

Shetland

Noss

8,652

11,786 2014

+36

+2.9

Shetland

Foula

919

1,226 2013

+33

+3.3

Shetland

Fair Isle

1,875

4,291 2018

+129

+6.1

Orkney

Noup Head

14

1,148 2018

+8,100

+37.0

Orkney

Sule Skerry

57

4,600 2018

+7,970

+36.8

Orkney

Sule Stack

4,618

4,550 2013

-1

-0.2

East Coast

Troup Head

1,547

3,847 2016

+149

+7.9

East Coast

Bass Rock

49,098

75,259 2014

+53

+4.4

East Coast

Bempton Cliffs

3,940

13,392 2017

+240

+9.9

The Minch

Berneray

Not counted

8 2016

n/a

n/a

Irish Sea

Ailsa Craig

27,130

33,226 2014

+22

+2.0

Irish Sea

Scar Rocks

2,394

2,375 2014

-1

-0.1

Irish Sea

Grassholm

32,094

36,011 2015

+12

+1.1

North West

Sula Sgeir

9,225

11,230 2013

+22

+2.2

North West

Flannan Isles

2,760

5,280 2013

+91

+7.5

North West

St Kilda

59,622

60,290 2013

+1

+0.1

North West

Rockall

Not counted

28 2014

n/a

n/a

 

Productivity

northern-gannet-uk-prod.jpg

Figure 2. Trend in UK breeding productivity (no. of chicks fledged per pair) of northern gannet 1986-2018. Based on SMP data; view the methods of analysis.

 

Gannet productivity has varied very little since monitoring started in 1986. At monitored colonies, productivity generally lies between 0.60-0.90 chicks per breeding pair over the study period (Figure 2). It is thought that because gannets can travel great distances (up to 500 km) from their nest site to forage9 and they are adaptable in what they eat (including live fish of various species and discards from the fishing industry), they rarely encounter food shortages. This and high adult survival rates, may be the main factors behind observed population increases.

Analysis of the SMP dataset found mean productivity of northern gannets to be 0.69 chicks per nest per year between 1986 and 200810. The quality of the dataset meant a change in productivity of 10% or more would be detected with confidence. Using available life history information (population size, clutch size, age at first breeding and survival rates of different age classes), it was predicted that if this level of productivity were maintained then northern gannet populations may decline by 59% within 25 years. Results from population viability analysis further suggested that if productivity is less than one, such a decline is likely. Because populations of northern gannets are currently increasing and productivity can never be above one for a species that lays a single egg this suggests that survival (which is not currently measured as part of the SMP), or some other parameter, may be underestimated.

The new EU Common Fisheries Policy came into effect in 2014. It included the obligation that all catches of regulated commercial species had to be landed and counted against quota. From 2015 to 2019, the landing obligation was phased in across the majority of EU fisheries. This is likely to impact on seabird populations that feed on discards. Species native to the north-east Atlantic that are currently extensively exploiting fishery discards are kittiwake, herring gull, lesser black-backed gull, great black-backed gull, great skua, northern fulmar and the northern gannet11. It is, therefore, possible that this decline in discards may affect the growth rate of the UK gannet population in the future.

 

Scotland

Population estimates and change 1969–2013/14 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Gannet Census

(2003–2004)

Gannet Census

(2013–2014)

UK Population estimate (AON/AOS*)

96,860

127,867

182,511

243,505

% change since previous census   

n/a

+32

+43

+33

*AON/AOS = Apparently Occupied Nests/Sites

 

Breeding abundance

The few colonies counted annually tend to be smaller colonies, which often increase at a greater rate than large colonies leading to bias in any estimated trends. Thus, only data from national censuses, when all colonies are surveyed, are considered to show an accurate trend. Northern gannet populations in Scotland have been steadily increasing since 1969/70 when 96,860 AON/AOS were recorded; numbers increased by 32% by the time of the Seabird Colony Register and then by 43% by the time of the gannet census in 2003 and 2004. All 16 gannet colonies in Scotland were counted in 2013 and 2014 (see Table 1 in UK section) with combined colony totals indicating that Scotland currently holds 243,505 apparently occupied sites (58% and 46% of the east Atlantic and world populations, respectively)5. Numbers were divided very unevenly between the colonies with Bass Rock (now the world’s largest colony), St Kilda and Ailsa Craig together holding 70% of the Scottish population. A new colony on Berneray was formed in 2007 and held eight AON in 2016. Breeding may also now be regular on Rockall where 28 AOS were recorded in 2014, although all nests were subsequently lost in a storm5. Numbers at St Kilda, Sule Stack and Scar Rocks were stable, but all other colonies had increased, some spectacularly. The colony on Sula Sgeir, the only one where the harvesting of young for food occurs, increased by 22% between 2004 and 2013, reversing the trend recorded between 1994 and 2004 during which this colony declined by 12%. Many of the gannet colonies appear to have plenty of unused, suitable nesting habitat and thus have considerable potential for further expansion. Overall the Scottish population increased by 33% between the 2003/04 and 2013/14 gannet censuses, or by 2.9% per annum5.

Note: During analysis of the 2014 survey, the images used to assess the population at Bass Rock in 2009 were re-counted. This gave a revised colony total of 60,853 AOS for 20097, 5,371 AOS higher than the total given in previous editions of this report and elsewhere. However, this change for 2009 does not affect any of the data presented in the tables for the UK and Scotland.

 

Productivity

northern-gannet-scotland-prod.jpg

Figure 3. Trend in breeding productivity (no. of chicks fledged per pair) of northern gannet in Scotland, 1986-2018. Based on SMP data; view the methods of analysis.

 

Data on northern gannet productivity have been collected each year at several gannetries in Scotland. Productivity at these monitored colonies has generally been high, seldom lower than 0.60 chicks fledged per pair, and appears to have increased over the study period. Productivity was low in the years 1987, 1990 and 1993, but the reasons for this are unclear. However, in 1993, productivity was severely reduced on Ailsa Craig due to poor weather (including snow and ice) in May. In 2015, northern gannet again had a successful breeding season on Ailsa Craig fledging 0.90 chicks per pair. During 2018, gannets in Scotland suffered a freezing spring followed by a very warm summer which may have contributed to the low productivity recorded that year (0.73 chicks fledged per pair).

 

England

Population estimates and change 1969–2013/14 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Gannet Census

(2003–2004)

Gannet Census

(2013–2015)

 Population estimate (AON/AOS*)

18

780

3,940

12,494

% change since previous census   

n/a

+4,233

+405

+217**

*AON/AOS = Apparently Occupied Nests/Sites

**change between census in 2003-04 and colony surveyed in 2015.

 

Breeding abundance

northern-gannet-england-ab.jpg

Figure 4. Abundance of northern gannet at Bempton Cliffs, England, 1986–2017.

 

Only one northern gannet colony exists in England, at Bempton Cliffs in Humberside. This colony has been increasing steadily since its formation in the 1960s although, in recent years, the growth rate appears to have escalated. A steep increase can be seen between counts in 2004 and 2017, although there is an uncharacteristic decrease in 2005. Between 2008 and 2009 numbers increased by just over 900 AON from 6,954 to 7,859. During the survey in 2009, a further 1,470 non-breeding immature birds were counted in 'club' areas of the gannetry which suggested further increases could be expected. Predictably, the high rate of increase was sustained in 2017, when 13,392 nests were counted. On average, approximately 700 AON have been added each year since 2009. Gannets at Bempton Cliffs were not counted in 2018.

 

Productivity

The productivity of gannets breeding at Bempton Cliffs shows no statistically significant variation over time; on average 0.80 chicks were fledged per nest between 1986 and 2018.

 

Wales

Population estimates and change 1969–2013/14 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Gannet Census

(2003-2004)

Gannet Census

(2013-2015)

Population estimate (AON/AOS*)

16,128

28,545

32,095

39,011

% change since previous census   

n/a

+77

+12

+21**

*AON/AOS = Apparently Occupied Nests/Sites

**change between census in 2003-04 and colony surveyed in 2015.

 

Breeding abundance

northern-gannet-wales-ab.jpg

Figure 5. Abundance of northern gannet on Grassholm, Wales, 1986–2015.

 

There is just a single gannet colony in Wales, although occasionally single pairs have set-up territories elsewhere without colonies becoming established. Changes in the size of the Grassholm gannetry have been documented since its foundation around 1820. Since the 1940s, when 6,000 apparently occupied sites (AOS) were estimated, the colony has grown rapidly, with 15,500 AOS estimated by aerial survey in 1964. Since 1984, counts have been made from aerial photographs, varying in quality of resolution and coverage. In 2009, using high resolution digital images, 39,282 AOS were recorded – making it the third largest gannetry in the UK and Ireland. The most recent survey in 2015 counted 36,011 AOS.

Directly comparable with counts in 1984, 1999 and 2004, in terms of image quality and coverage, the 2015 count suggests that the colony has decreased by 8% since 2009.

 

Productivity

Productivity data have been collected on Grassholm since 2002. Analysis shows no statistically significant variation over time; an average of 0.71 chicks are fledged per nest each year.

 

Northern Ireland

Northern gannet does not breed in Northern Ireland.

 

Republic of Ireland

Population estimates and change 1969–2013/14 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Gannet Census

(2004)

Gannet Census

(2013-14)

Population estimate (AON/AOS*)

21,655

24,740

36,111

47,946

% change since previous census   

n/a

+14

+46

+33

*AON/AOS = Apparently Occupied Nests/Sites

 

Breeding abundance

Census results indicate that northern gannet populations in the Republic of Ireland have been increasing since 1969/70. In 2004, when all gannetries in Ireland were counted, five colonies were known (Little Skellig, Bull Rock, Great Saltee Ireland’s Eye and Clare Island), supporting 36,111 AOS. A census of gannet colonies in Ireland in 2013–2014 showed an increase of 32.8% (47,946 AOS) compared to the 2004 census12. A new (sixth) colony on Lambay had established since the last census (in 2007) and significant increases at all sites were recorded, although Ireland’s Eye apparently reached capacity between 2004 and 2014. The largest proportion of the Irish population nests on Little Skellig, which held 29,683 AOS in 2004 and 35,294 AOS in 2014, an increase of 19%. Factors underlying the sustained growth of the Irish gannet population are not known, but food supply cannot be a limiting factor up to the present time. Recent changes to the EU Common Fisheries Policy have led to a reduction in discards which may, in due course, effect gannet population growth11. No northern gannet abundance data from the Republic of Ireland have been submitted to the SMP since 2015.

 

Productivity

Data submitted to the SMP on the productivity of northern gannets in the Republic of Ireland are sparse; thus, no meaningful average productivity value can be given.

 

All Ireland

Population estimates and change 1969–2013/14 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Gannet Census

(2004)

Gannet Census

(2013-14)

Population estimate (AON/AOS*)

21,655

24,740

36,111

47,946

% change since previous census   

n/a

+14

+46

+32**

*AON/AOS = Apparently Occupied Nests/Sites

 

Breeding abundance

Within Ireland, the northern gannet only breeds in the Republic of Ireland. Thus, all data and text for the Republic of Ireland is also pertinent to the status of the species for the whole of Ireland.

 

Productivity

This species does not breed in Northern Ireland and data submitted to the SMP on the productivity of northern gannets in the Republic of Ireland are sparse; thus, no meaningful average productivity value can be given.

 

Isle of Man

Northern gannet does not breed on the Isle of Man.

 

Channel Islands

Population estimates and change 1969–2015 (census data)

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Seabird Census

(1998–2002)

Channel Islands Census

(2015)

Population estimate (AON/AOS*)

3,000

4,521

5,920

8,686

% change since previous census   

n/a

+51

+31

+47

*AON/AOS = Apparently Occupied Nests/Sites

**change between census in 2003-04 and colony surveyed in 2015.

 

Breeding abundance

northern-gannet-channel-isles-ab.jpg

Figure 6. Abundance of northern gannet on Ortac and Les Etacs, 1986–2015.

 

There are two gannetries in the Channel Islands, on Ortac and Les Etacs, which became established during 1940-45. Small in size compared to some other gannet colonies around the British and Irish coastlines, they nevertheless also show the familiar upward trend in numbers since Operation Seafarer visible at other gannetries. However, the most recent surveys, in 2015, recorded 2,777 AON on Ortac with 5,909 AON on Les Etacs. In summary, Les Etacs has apparently been increasing at a steady rate since 1986 while numbers on Ortac appear relatively stable over the same time period13.

 

Productivity

Data submitted to the SMP on the productivity of northern gannets on the Channel Islands are sparse; thus, no meaningful average productivity value can be given.

 

Top

UK phenology, diet, survival rates

No data have been collected as part of the Seabird Monitoring Programme.

Top

References

1 Murray, S. and Wanless, S. 1986. The status of the Gannet in Scotland 1984–85. Scottish Birds, 14, 74–85.

2 Murray, S. and Wanless, S. 1997. The status of the Gannet in Scotland in 1994–95. Scottish Birds, 19, 10–27.

3 Murray, S., Wanless, S. and Harris, M.P. 2006. The status of the Northern Gannet in Scotland in 2003–04. Scottish Birds, 26, 17–29.

4 Wanless, S., Murray, S. and Harris, M.P. 2005. The status of Northern Gannet in Britain and Ireland in 2003/2004. British Birds, 98, 280–294.

5 Murray, S., Smith, I. and Smith, A. 2014. Gannet and Guillemot breeding on Rockall, North Atlantic. Scottish Birds, 34, 13–15.

6 Murray, S., Wanless, S. and Harris, M.P. 2014. The Bass Rock – now the world’s largest Northern Gannet colony. British Birds, 107, 765–769.

7 Murray. S., Harris. M.P. and Wanless, S. 2014. An aerial survey of Northern Gannets Morus bassanus on Scar Rocks, southwest Scotland, in 2014. Seabird, 27, 104–109.

8 Murray, S., Harris, M.P. and Wanless, S. 2015. The status of the gannet in Scotland in 2013-14. Scottish Birds, 35, 3-18.

9 Hamer, K.C., Phillips, R.A., Hill, J.K., Wanless, S. and Wood, A.G. 2001. Contrasting foraging strategies of Gannets Morus bassanus at two North Atlantic colonies. Marine Ecology Progress Series, 224, 283–290.

10 Cook, A.S.C.P. and Robinson, R.A. 2010. How representative is the current monitoring of breeding success in the UK? BTO Research Report, No. 573, BTO, Thetford.

11 Bicknell, A.W.J., Oro, D., Camphuysen, J.C. and Votier, S.C. 2013. Potential consequences of discard reform for seabird communities. Journal of Applied Ecology, 50, 649–658.

12 Newton, S.F., Harris, M.P. and Murray, S. 2015. Census of Gannet Morus bassanus colonies in Ireland in 2013-2014. Irish Birds, 10, 215–220.

13 Veron, M. and Veron, C. 2016. Seabird Count 2015; monitoring the status of Guernsey’s Seabirds. La Société Transactions, Channel Islands.

Top

Partners

Data have been provided to the SMP by the generous contributions of its partners, other organisations and volunteers throughout Britain and Ireland. Partners to the SMP are: BirdWatch Ireland; The British Trust for Ornithology; UK Centre for Ecology and Hydrology; Natural Resources Wales; Department of Environment, Food and Agriculture (Isle of Man); Department of Environment, Heritage and Local Government (Republic of Ireland); States of Guernsey Government; JNCC; Manx Birdlife; Manx National Heritage; The National Trust; National Trust for Scotland; Natural England; Northern Ireland Department of Agriculture, Environment and Rural Affairs; The Royal Society for the Protection of Birds; Scottish Natural Heritage; Seabird Group; Shetland Oil Terminal Environmental Advisory Group; Scottish Wildlife Trust. More about the SMP partners >>

 

Image of Northern gannet appears courtesy of Ian Rendall ©, is subject to international copyright law and may not be reproduced in any form whatsoever.

Top

Categories:

SMP Report 1986–2018

Published: .

Back to top