The Northern Gannet Trilogy. Part II – You Will Not Be Surprised By What Seabirds Eat

The Northern gannet eat fish. In the latter part of the first decade of this century, French scientists Ms. Emeline Pettex and Mr. Jean-Baptiste Pons, spent a few weeks at Gjesværstappan Nature Reserve one summer after another. The information they mustered was to master the gannet beyond just dietary measures. Compared to other colonies in Europe, the findings reveal some seabird secrets: In particular, between the colonies at Store Ulvøyholmen in Lofoten and Gjesværstappan in Nordkapp. Part of the questions to be answered by the research is:

  1. Why the colony in Nordkapp is getting bigger?
  2. Why colonies in Lofoten are struggling?

Of the dozen colonies establish in Lofoten after 1960, most colonies are now extinct. Could it be that it is more difficult to fish in Lofoten?

Estimates of stock sizes of pelagic fish from the Norwegian and Barents Sea (ICES2009). Emeline PETTEX, Ecologie alimentaire du fou de Bassan Morus bassanus en Atlantique Nord à des échelles spatio-temporelles multiples.UNIVERSITE MONTPELLIER, France. 2011

No, to the contrary: The smaller the colony, the easier it is to fish. At North Cape the gannet diet consist of:

  • Herring
  • Garfish
  • Gadids (saithe and cod)
  • Mackerel
  • Sand eels

The longest catch was a mackerel stretching 40 cm. In Lofoten, the diet was saithe, herring, mackerel and sand eel. Food shortage is an unfamiliar term.

As a whole, research shows that the gannet spend more effort fishing if they are breeding in “bigger cities”. The gannet at Gjesværstappan outnumbers Store Ulvøyholmen four times. In the very large colonies such as Bass Rock in Scotland, the gannet will not return to the nest until the next day. Here, the pair must often leave their offspring unattended.

Not so in Norway. In 2010, mean fishing/foraging trip was 8.3 hrs at Gjesværstappan. In 2007, North Cape gannets were fishing almost two times longer than the “lofotarians”.  Another big difference was the fishing area. The gannet in Gjesvær had a fishing area of close to 14 000 square kilometer. In Lofoten, the area was close to a mere 1 800 square kilometer. On a normal fishing trip the gannet in Gjesvær would fly a distance of 190 kilometers. In Lofoten, the flying distance would be 110 kilometers.

Comparison of foraging trip duration in relation with the colony size among Northern gannet colonies from Norway, British Isles and France. Emeline PETTEX, Ecologie alimentaire du fou de Bassan Morus bassanus en Atlantique Nord à des échelles spatio-temporelles multiples.UNIVERSITE MONTPELLIER, France. 2011

The GPS devices on equipped gannets show how the gannet were fishing. The North Cape gannet will cover a distance from the nest to the fields of fishing beyond the horizon. Cruising at 50 km/h, at some 30 meters above sea level, the gannet would sail more or less straight to the fishing ground, and back. A daily new fishing route was more often the case than not. It had four main routes in 2009:

  • West towards Rolvsøya
  • Southwest through Kobbefjord
  • North of North Cape
  • Southeast to Porsangerfjord

Along these routes are fishing hotspots.

Main feeding routes followed by Northern gannets. Emeline PETTEX, Ecologie alimentaire du fou de Bassan Morus bassanus en Atlantique Nord à des échelles spatio-temporelles multiples.UNIVERSITE MONTPELLIER, France. 2011

Without visual points to guide it, the gannet knows where to fish. It is a master of finding profitable areas for fishing. It must be able to cash in on:

  • Physical features of ocean basin
  • Tidal fronts
  • Upwelling areas
  • Shelf edges and so on

This information is also essential for fishermen.

How the gannet have this knowledge is still not quite clear. The gannet do not necessarily fish together with other gannets. It seems, they have an individual fishing plan. Must likely, it is a combination of:

  • Community wisdom
  • Individual experiment and memory
  • Sight
  • Olfactory input

What is also interesting is that the gannet can change prey and fishing practices from one period to another, one year to the other. This know-how tells us that the individual gannet are very adaptable to changes in its fishing environment. Adaptable birds – Strong colonies.

The gannet’s game is the smaller seabirds’ gain. The game is competing with the smaller seabirds for the same food/prey. So there is more food for the auks, for instance, when the gannet is around and eating the auk competitor. The gannet is a steward of the balance of nature.
In conclusion, the fishing situation, an inability to get enough food for the gannet itself and its chick is not the reason for the extinction of gannet colonies in the Lofoten area. The Lofoten gannet spend less time and cover less distance compared to the North Cape gannet in gathering food by far.

Some say the answer to that question might be the rise of the gannet chick predator: The White-tailed Eagle. The local guard in the Lofoten area says that he saw eagles attacking adults. Harassment and disturbance could be the cause. At Storstappen, smaller preys are available for White-tailed Eagles (Auks, Kittiwakes). Much easier to predate, than the dangerous gannets. The scientists think that the huge colonies of auks and gulls might “protect” gannets from eagle disturbance.

ø Question:

What do you think is the worst threat to the seabirds?

The Northern Gannet Trilogy

The seabirds at Gjesværstappan is a surprising attraction at North Cape. In a series with three blog post you can fly into the life of the beautiful gannet.

I. The Secrets of the Regal White Bird

II. More details on what the Northern Gannet eat

III. What does Thomas Cook and Northern Gannets have in common

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