Northern Gannet Morus bassanus

Status;  International importance;  Population estimates;  Distribution;  Annual abundance/ productivity; Phenology/diet/survival

 

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Description

Northern Gannet vignette

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 18 gannetries around the British Isles, 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:

EC Birds Directive - migratory species

Amber listed in Birds of Conservation Concern 4 (2015 update)

(further information on Conservation Designations for UK Taxa)

Amber listed in  Birds of Conservation Concern in Ireland 2014-2019 (2014 update)


International importance

 

UK Population % Biogeographic Population % World Population
293,200 AOS* 418,441 55.6

 

*AOS = 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.

 


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. Since then, two full censuses were carried out in 2004/05 and 2013-15.

 

 

Operation Seafarer

(1969-70)

Seabird Colony Register

(1985-88)

Gannet Census

(2003-04)

Gannet Census

(2013-14)

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.

 


Distribution/abundance

 

The Seabird 2000 census provides the most comprehensive recent assessment of the distribution and abundance of breeding seabirds. Although many large northern gannet colonies were not surveyed during this census, numbers found in different regions, and a map showing the location and size of colonies, is provided in the Seabird 2000 northern gannet results page (PDF, 2.0 mb).

 

An interactive map is available on the NBN Gateway, where you can filter to display only the Seabird 2000 data.  For more recent, but less comprehensive, coverage view the distribution on the NBN with all available contributing datasets.

 

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

 


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% CLs 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.   

 



 

Breeding abundance

 

Gannet Abundance UK 2015

Figure 1: Trend in UK abundance index of northern gannet 1986-2015.

 

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 colonies, which increase at a greater rate than do large 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 and reached 218,000 AON in 2003/04.

All UK colonies have been surveyed at least once since the last census (Table 1). Most have continued to increase, except the gannetries at Sule Stack (Orkney) and Scar Rocks (Wigtown), and new gannetries continue to be formed (Berneray, Western Isles) or re-colonised (Rockall, Western Isles). All Scottish colonies were surveyed in 2013 or 20145,6,7,8. Data from these, with the addition of the most recent counts from Bempton Cliffs (Humberside) and Grassholm (Dyfed) in 2015, suggests the UK gannet population is now at least 293,161 AOS (the dominant survey unit). This would represent an increase of 34% since the 2003/04 gannet census.

 

Table 1: Recent counts at UK gannetries compared to counts during the previous 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 3,591 2014 +92 +6.7
Orkney Noup Head 14 751 2014 +5,264 +48.9
Orkney Sule Skerry 57 1,870 2013 +3,181 +47.4
Orkney Sule Stack 4,618 4,550 2013 -1 -0.2
East Coast Troup Head 1,547 6,456 2014 +317 +15.4
East Coast Bass Rock 49,098 75,259 2014 +53 +4.4
East Coast Bempton Cliffs 3,940 12,494 2015 +217 +11.1
West Coast Sula Sgeir 9,225 11,230 2013 +22 +2.2
West Coast Flannan Isles 2,760 5,280 2013 +91 +7.5
West Coast St Kilda 59,622 60,290 2013 +1 +0.1
West Coast Rockall N/c 28 2014 N/a N/a
West Coast Berneray 0 2014 N/a N/a
West Coast Ailsa Craig 27,130 33,226 2014 +22 +2.0
West Coast Scar Rocks 2,394 2,375 2014 -1 -0.1
West Coast Grassholm 32,094 36,011 2015 +12 +1.0

 

Productivity

 

UK gannet productivity trend

Figure 2: Trend in UK breeding productivity (no. of chicks fledged per pair) of northern gannet 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

Gannet productivity has varied very little since 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 km9) from their nest site to forage, and because they are adaptable in what they eat (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 breeding success 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 breeding success 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 breeding success were maintained then northern gannet populations may decline by 59% within 25 years. Results from population viability analysis further suggested that if breeding success is less than one, such a decline is likely. Because populations of northern gannets are currently increasing and breeding success 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.

 

 

Population estimates and change 1969-2013/4 (census data)

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Gannet Census    

(2003-2004)

Gannet Census

(2013-14)

Population estimate (AON/AOS*) 96,860 127,867 182,511

243,505

% change since previous census    N/a +32 +43 +33

 

* AON = Apparently Occupied Nests/Sites

 

Breeding Abundance

 

The few colonies counted annually tend to be smaller colonies, which increase at a greater rate than do 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 (East Lothian, now the world’s largest colony), St Kilda and Ailsa Craig (Kyle and Carrick) together holding 70% of the Scottish population. A new colony had been formed since the last census; gannets started to nest on Berneray in 2007 with the colony now holding seven AON in 2014. 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 Sule Stack and Scar Rocks were stable, but all other colonies had increased, some spectacularly. The colony on Sula Sgeir (Western Isles), the only one where harvesting of young by humans for food occurs, had increased by 2.2% per annum, reversing the trend recorded between 1994 and 2004 during which this colony declined at 1.2% per annum. Many of the gannet colonies appear to have plenty of unused, suitable nesting habitat thus have considerable potential for further expansion. Overall the Scottish population increased by 33% between 2003 -2004 and 2013-2014 at an average rate of increase of 2.9% per annum5.

 

Note: During analysis of the 2014 survey, the images used to assess the population of the 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

 

UK gannet productivity trend

Figure 2: Trend in breeding productivity (no. of chicks fledged per pair) of northern gannet in Scotland, 1986-2015. Based on SMP data; view the methods of analysis (PDF 158 kb).

 

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 as to why are often not clear. However, in 1993, breeding success 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.

 

 

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

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Gannet Census    

(2003-2004)

Gannet Census

(2013-14)

Population estimate (AON/AOS*) 18 780 3,940 12,494
% change since previous census    N/a +4,233 +405 +217**

 

* AON = Apparently Occupied Nests/Sites

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

 

Breeding Abundance

 

Gannet Bempton Cliffs SPA abundance

Figure 1: Abundance of northern gannet at Bempton Cliffs (Humberside), England, 1986-2015.

 

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 2015, although there is an uncharacteristic decrease in 2005. Between 2008 and 2009 numbers increased by just over 900 nests 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 2015, when 12,494 nests were counted. On average, over 1,000 new breeding pairs have been added each year since 2009.

 

Productivity

 

The productivity of gannets breeding at Bempton Cliffs shows no statistically significant variation over time; on average 0.82 chicks are fledged per nest between 1986 and 2015.

 

 

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

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Gannet Census    

(2003-2004)

Gannet Census

(2013-14)

Population estimate (AON/AOS*) 16,128 28,545 32,095

39,011

% change since previous census    N/a +77 +12 +21**

 

* AON = Apparently Occupied Nests/Sites

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

 

Breeding Abundance

 

Gannet Grassholm abundance 2015

Figure 1: Abundance of northern gannet on Grassholm (Dyfed), Wales, 1984-2015.

 

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 suggested that the colony has slightly decreased by 8% since 2009.

 

Productivity

 

Breeding success data has been collected on Grassholm since 2002. Analysis of the available data shows no statistically significant variation over time; an average of 0.74 chicks are fledged per nest each year.

 

 

Northern gannet does not breed in Northern 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 47,754
% change since previous census    N/a +14 +46 +32**

 

* AON = Apparently Occupied Nests/Sites

** change between census in 2003-04 and colony surveyed in 2011.

 

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, there five colonies were known (Little Skellig (Kerry), Bull Rock (Cork), Great Saltee (Wexford) Ireland’s Eye (Dublin) and Clare Island (Mayo)), supporting 36,111 AOS. A census of gannet colonies in Ireland in 2013-2014 showed an increase of 32.8% (47,946 AOS). A new (the sixth) colony on Lambay had established since the last census 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 (Co. Kerry), which held 29,683 AOS in 2004 and 35,000 AOS in 2014, an increase of 18%. 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 in European fisheries policy on discarding may in due course reduce food supply and availability for gannets and this might curtail further population expansion.

 

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.

 

 

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 47,754
% change since previous census    N/a +14 +46 +32**

 

* AON = Apparently Occupied Nests/Sites

** change between census in 2003-04 and colony surveyed in 2011.

 

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.

 

 

Northern gannet does not breed on the Isle of Man.

 

 

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

 

 

Operation Seafarer    

(1969-70)

Seabird Colony Register    

(1985-88)

Gannet Census    

(2005)

Gannet Census

(2013-14)

Population estimate (AON/AOS*) 3,000 4,521 7,409

7,885

% change since previous census    N/a +51 +64 -6

 

* AON = Apparently Occupied Nests/Sites

 

Breeding Abundance

Gannet Abundance Channel Islands 2015

Figure 1: Abundance of northern gannet on Ortac and Les Etacs (Channel Islands), 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 2011, recorded 2,120 AON on Ortac with 5,765 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 period.   

 

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.

 

 


UK phenology, diet, survival rates

 

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

 


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

6 Murray, S., Smith, I. and Smith, A. 2014a. Gannet and Guillemot breeding on Rockall, North

Atlantic, Scottish Birds 34: 13–15.

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

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

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.

 


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; 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 Environment Agency; 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.