Breeding abundance

Figure 1: Trend in UK abundance index of northern gannet 1986-2010.

Given the logistical problems of sampling gannet colonies, annual sampling of all but the smaller colonies is impractical. Instead, decadal censuses have been undertaken, the last in 2004/5. Figure 1 shows interpolated and extrapolated values from three of these censuses, expressed as an index. In the longer term, the UK gannet population increased from 113,000 pairs in 1969/70 to 175,000 in 1984/5.

Productivity

Gannet productivity has varied very little since 1986. At the colonies monitored, the mean value between 1986-2010 was 0.72 chicks per breeding pair with no statistically significant annual variation within the sample. It is thought that because gannets can travel great distances (up to 500 km¹) from their nest site to forage, and because they are adaptable in what they eat (live fish and discards), they rarely encounter food shortages. This, and high adult survival rates, may have enabled the population increases shown above.

Population estimates and change 1969-2004/5 (census data)

* AON = Apparently Occupied Nests

Breeding Abundance

Figure 1: Abundance index of northern gannet in Scotland during three national censuses.

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 shown (Figure 1 and table above). Northern gannet populations in Scotland have been steadily increasing since 1969/70 although the rate of increase between the two most recent surveys has lessened.

Productivity

Figure 2: Trend in breeding productivity (no. of chicks fledged per pair) of northern gannet in Scotland, 1986-2010. Based on SMP data; view the methods of analysis (PDF 158 kb).

Data on northern gannet productivity has 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 in the last few years has been remarkably consistent.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Breeding Abundance

Figure 1: Abundance of northern gannet at Bempton Cliffs, England 1986-2010.

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 large increase can be seen between counts in 2004 and 2008, with an uncharacteristic dip in 2005, and between 2008 and 2009 numbers increased by just over 900 nests from 6,954 to 7,859. With a further 1,470 non-breeding immatures in 'club' areas of the gannetry, further increases are likely in the near future.   

Productivity

Analysis of productivity data from Bempton revealed there was no statistically significant variation over time with productivity averaging approximately 0.79 chicks fledged per pair per year.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Breeding Abundance

Figure 1: Abundance of northern gannet on Grassholm, Wales 1986-2010.

Like England, there is just a single gannetry 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 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. The most recent survey in 2009, using high resolution digital images, indicates that the gannetry now holds 39,282 AOS - the third largest in the UK and Ireland. Directly comparable with counts in 1984, 1999 and 2004, in terms of image quality and coverage, the 2009 count raises the possibility that the growth rate is increasing.

Productivity

Relatively few data on productivity are available from Grassholm for analysis.

This species does not breed in Northern Ireland.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Breeding Abundance

Figure 1: Abundance of northern gannet at five colonies in the Republic of Ireland, 1986-2010.

Few colonies are counted annually and these tend to be smaller colonies, which tend to increase at a greater rate than do large colonies. For example, Lambay was colonised between 2004 (when no birds bred) and 2007 (87 AON), rising to 187 AON in 2009 although, unusually, numbers fell to 138 AON in 2010. The gannetry at Ireland's Eye also increased in size and in 2010 now holds 360 AON (26% more than in 2004). Census results indicate that northern gannet populations in the Republic of Ireland have been increasing since 1969/70.

Productivity

Few systematic productivity data have been collected for northern gannet in the Republic of Ireland as part of the SMP.

Northern gannet nests only in the Republic of Ireland. Thus all data and text displayed for the Republic of Ireland is fully relevant to the whole of Ireland but is not repeated here.

This species does not breed on the Isle of Man.

Population estimates and change 1969-2002 (census data)

* AON = Apparently Occupied Nests

Breeding Abundance

Figure 1: Abundance of northern gannet on Ortac and Les Etacs, Channel Islands, 1986-2010.

There are two gannetries in the Channel Islands, on Ortac and Les Etacs. Small in size compared to others around the British and Irish coastlines, they nevertheless also show the familiar upward trend visible in the others since Operation Seafarer, although Les Etacs has apparently been increasing at a greater rate than Ortac since 1986. The most recent surveys in 2005 recorded 2,547 AON on Ortac with 4,862 AON on Les Etacs.   

Productivity

Little systematic productivity data have been collected for northern gannet in the Channel Islands as part of the SMP.