Gannet - 2013 research

Article from Science Daily, March 14, 2013

The European Parliament recently voted to scrap the controversial discards policy, which has seen fishermen throwing thousands of edible fish and fish waste back into the sea because they have exceeded their quotas.

Scientists at Plymouth University believe this could have a negative impact on some seabirds, which have become used to following the fishing vessels and are increasingly reliant on their discards.

But they say others could return to using foraging as their sole source of food, as long as there are sufficient numbers of fish to meet their needs.

Dr Stephen Votier, Associate Professor in Marine Ecology at Plymouth University, led the study. He said: "Policy changes can have unforeseen consequences, and the recent decision on the EU discards policy will pose challenges for a number of species. Many seabirds have come to rely to some extent on fishing vessels for food and globally, commercial capture fisheries generate huge quantities of discards. However, we believe there is a level of resilience among seabirds which means they will be able to overcome these challenges." The study focused on populations of northern gannets on Grassholm Island, in Wales, with tiny cameras and GPS trackers being attached to birds to monitor their foraging habits.

The cameras captured more than 20,000 images, allowing scientists for the first time to analyse where the birds had flown to source food, precisely what they had fed on, and other details such as their sex and reproductive status.

The findings showed 42% of birds regularly targeted fishing vessels, as well as searching for naturally occurring prey, while 81% of male gannets used fishing vessels to source food and 30% of female birds did so.

Dr Votier added: "We have used cutting-edge technology to reveal the private lives of seabirds at sea -- in this instance how they interact with fisheries -- and the findings suggest scavenging is more common in this species than previously thought. This suggests a discard ban may have a significant impact on gannet behaviour, particularly so for males, but a continued reliance on 'natural' foraging shows the ability to switch away from discards, but only if there is sufficient forage fish to meet their needs in the absence of a discard subsidy." The research study, which also involved scientists from the Plymouth Marine Laboratory and the Centre d'Etudes Biologiques de Chize in France, was conducted under licence from the Countryside Council for Wales and the British Trust for Ornithology.

It received funding from the National Environment Research Council, and the full findings are published in the latest issue of the PLOS ONE scientific journal.

Stephen C. Votier, Anthony Bicknell, Samantha L. Cox, Kylie L. Scales, Samantha C. Patrick. A Bird’s Eye View of Discard Reforms: Bird-Borne Cameras Reveal Seabird/Fishery Interactions. PLoS ONE, 2013; 8 (3): e57376 DOI: 10.1371/journal.pone.0057376

Update on Tuesday, November 12, 2013 at 8:27AM by Pembrokeshire Avifauna committee

More on this story at BBC Nature including a video clip - a gannet's eye view of the world.

Gannet - 1949

Sula bassana

The colony on Grassholm now (1948) numbers approximately 7,000 pairs.  Its history is to be found in various places: in I knew and Island by R.M.Lockley; and in The Breeding, Distribuion, History and Population of the North Atlantic Gannet by J.Fisher and H.G.Vevers (Journal of Animal Ecology, 1943, XIX 177-8).

R.M.Lockley, G.C.S.Ingram, H.M.Salmon, 1949, The Birds of Pembrokeshire, The West Wales Field Society

Gannet - 2003-07

Despite being relatively widespread around the coast, gannets are confined to breeding on just one small remote island, Grassholm – about 12 miles off the Pembrokeshire mainland. Here they nest at very high density, the only breeding colony for this species in Wales. Because of the importance of the Gannet population on Grassholm (in European and indeed World terms) the island has been designated a Special Protection Area for them (under the EC Directive on the conservation of wild birds (79/409/EEC).  

Counting the population is a special operation requiring skilled observers. The colony is now so dense that visitors are no longer able to land on the island as this causes too much disturbance. Because of this, assessments of the colony population size have to be made from aerial surveys usually done in late summer. This is done by counting the number of apparently occupied nest sites (AOS) observed in photographs. This process is now considerably aided by modern high quality digital photographic equipment and computer mapping software.

The most recent aerial survey during the 2003-07 atlas period was undertaken in July 2004 by ornithologists from the Centre for Ecology and Hydrology with a follow up ground survey (after the young had fledged) in September the same year to confirm the colony boundary areas. (Wanless et al 2005).

During the 1984-88 atlas period, the population estimate was 28,600 AOS in 1984–85, with an estimated 30,000 AOS in 1986 (Lloyd et al. (1991).

By 1999, the population was an estimated 30,688 AOS. In 2004 the population had risen to 32,094 AOS; an increase in colony size between 1999 and 2004 of 4.6% (a rate of approx 0.7% per annum). Comparison with other UK and Irish Gannet colonies in 2004 indicated that Grassholm is the third largest northern Gannet colony in Britain, supporting approximately 12% of the UK and Irish population, about 8% of the World population (Wanless, et al, 2005).

If the well documented population expansion and gradual spread of the colony across Grassholm continues, it is interesting to speculate where a new Gannet colony may form if they eventually run out of space! For a few years, (during the 2003-07 atlas recording period) one Gannet appeared to be resident on St Margaret’s Island each summer, making a nest and even laying an egg in one year. However, no mate was ever confirmed and successful breeding did not occur, so Grassholm currently retains its status as the only Gannet colony in Pembrokeshire and in Wales.  

Bob Haycock

Update on Monday, May 7, 2012 at 10:30AM by Pembrokeshire Avifauna committee

Since the atlas fieldwork period was completed, another aerial survey was undertaken in 2009. This survey produced a mean population estimate of 39,292 AOS. Between 2004 and 2009 numbers of Gannets on Grassholm had therefore increased by 22.4%, at a mean rate of 4.1% pa. Grassholm remains the third largest gannetry in the UK; by 2009 holding approximately 15% of the UK and Irish population and 9.5% of the world population (Murray, 2009).

Bob Haycock

Gannet - 1994

Breeding resident

The only breeding site for the Gannet in Wales is on Grassholm. Williams (1978) provides a résumé of the history of the colony which seems to have been established shortly before 1860, when 20 pairs were present, though Gurney (1913) suggests birds may have been present as early as 1820.

They were beset by problems during the early years, mainly from egg collectors, while in 1890 members of the Cardiff Naturalists Society, who were camping on the island at Whitsun, witnessed a party of naval and military officers from Pembroke Dock shooting Gannets and taking and smashing eggs. The miscreants were brought before the bench at Haverfordwest in August of that year and fined a total of £22.17s. in what the magistrates described as "a somewhat novel case ... but it was also a charge that could not be passed over lightly."

The growth of the colony aroused the interest of a succession of ornithologists, resulting in a series of nest counts, initially made by eye, then by photographs taken on the ground first by Acland and Salmon (1924), followed by the first aerial survey in 1956 (Lockley 1957); this remains the standard census method (see Table 1). Colony growth has not been uniform, Nelson (1978) demonstrating that Grassholm must have exported breeding birds in the 1960s but imported them in the 1920s and 1970s.

A fresh count of the Grassholm gannetry is clearly overdue as observations show a continued advance by the Gannets. The days are gone when visitors stood on the summit of the island viewing the colony spread below; the high point is now fully occupied by breeding birds which are advancing southwards across the island. The RSPB, who have owned Grassholm since 1948, have had to prohibit landing at two points in order to minimise disturbance to birds nesting in their vicinity, it being a matter of conjecture how long it will be before the sole remaining landing point is also occupied by breeding birds.

With apparently plenty of food to support their ever increasing numbers and few enemies the Grassholm Gannets have little to fear save for man­made hazards. The most obvious of these is that posed by entanglement in nylon lines and netting. The Gannets gather prodigious quantities of nesting material, normally seaweeds with the addition of grasses pulled from near the colony. However, anything floating in the sea which can be carried is likely to be incorporated into the nest. For the past two decades this has included nylon, and some nests can be bright orange in colour, so significant is the quantity. Adults and chicks can become entangled and deaths occur, either through birds being anchored to their nests or by becoming so entangled that they cannot fly properly.

Over 5,000 Gannets were ringed on Grassholm, largely by the staff of the Skokholm Bird Observatory, up until the late 1960s. There have been recoveries from as far apart as the Faeroes and Senegal, with most immatures following the traditional route south to west African waters where some remain for the first two years of life. Most adults do not travel so far but remain in home waters throughout the winter.

Large passages occur off Strumble Head in the autumn which probably include many birds from colonies other than Grassholm. Passage peaks in August, the average rate from 14 counts made in 1980 and 1981 being 180 birds per hour, the maximum 1,700 in five hours on 25 August 1980. An albino recorded at Strumble Head on 15 September 1985 was also seen passing Towan Head, Cornwall, on 16 September 1985, indicating through passage.

Although fairly sparsely distributed inshore during the winter months, typically less than ten at any locality, onshore gales temporarily push greater numbers towards the land; for example, up to 100 were seen at Strumble Head on 2 January 1988. Grassholm is usually deserted from about late October and reoccupied in January.

Fieldwork 1984-88

Red = breeding confirmed

Orange = breeding probable

Yellow = breeding possible

Donovan J.W. & Rees G.H (1994), Birds of Pembrokeshire

Gannet - 1980s winter

The BTO winter atlas showed that Gannets were present in a few coastal 10km squares during the winters of 1981-82, 1982-82 and 1983-84.

The coloured 10km squares represent 1-3 birds seen in a day.

Graham Rees

Gannet - 1970s breeding

Red = breeding confirmed

Orange = breeding probable

Yellow = breeding possible

Gannet - 1894

Species account from M Mathew, 1894, "The Birds of Pembrokeshire and its islands"

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