Tangled in the food web
|Puffins Credit: photos.com|
Several, but certainly not all, of the key seabirds of the Northeast Atlantic:
Northern fulmar: Fulmars look much like seagulls, but they can be distinguished by flight pattern: fulmars hold their wings stiffly and alternate between rapid wingbeats and long glides low over the water. They spend most of the year in the open ocean, migrating south in the winter. Young birds are valued for human consumption because of their strongly scented flesh. Fulmars are close relatives of petrels.
Northern gannet: These huge seabirds, with wingspans up to nearly six feet, fly with slow, graceful wingbeats and suddenly plunge in spectacular style to seize fish below the surface. The northern gannet is very successful in consuming discards from boats. It also steals food from other birds; when ranking species according to their robbery index (what they steal from other birds vs. what is stolen from them), the northern gannet, great black-backed gull, and great skua are at the top.
Great cormorant: They consume a wide variety of fish, especially small cod, haddock, or herring. Populations are increasing in Denmark and the Netherlands, but there is a marked decline in Scottish waters. Mass killing of this bird occurs because fishers believe great cormorants damage fish stocks. But there is no scientific evidence that killing any marine predator has enhanced any commercial fishery.
Shag: Similar in appearance to cormorants, and with a similar diet.
Gulls: Herring gulls predominate around fishing vessels in English waters. Black-backed gulls are also numerous at fishing boats near shore in the north and northwest of the UK. Seabirds prefer round fish to flatfish because they are easier to swallow and generally have a higher fat content.
Kittiwake: With a tern-like wingbeat, the black-legged kittiwake is highly maneuverable, and able to land on narrow ledges in strong winds. An opportunistic feeder, it feeds on small surface fish and invertebrates. It prefers live fishes over discard, and the species consumed most often are capelin (Barents Sea), young herring (Norwegian Sea), and sandeels (North Sea).
Arctic tern: Even though it is a small bird (weighing about four ounces), it migrates over 22,000 miles each year. Black markings under each wing and its bright red beak make the arctic tern stand out among other birds. In the North Sea, sandeels are the main part of the diet.
Guillemot (Black, Common): A relatively small seabird, black guillemots are adept at wing-propelled swimming, allowing them to dive above and into the kelp forest in nearshore waters, where they feed mainly on fish. The larger common guillemot, which is able to dive to 180 meters, uses fewer food items, which makes it vulnerable to reductions in a single food-source species. Because they have a long life-span, start reproduction at a late age, and rear only one chick a year, they are extremely vulnerable to factors affecting adult mortality (food shortage, bycatch in fishing gear, oil pollution, contamination, and so forth).
Puffin: A parrot-like beak, bright orange legs, and exceptionally rapid wingbeats readily identify the Atlantic puffin or "sea parrot." They hunt a variety of small fish, including herring, capelin, and sandeels. Puffins are excellent divers and can reach depths of 60 meters. They often feed far offshore and spend the entire winter at sea. Puffins can live 25 years or more (the Norwegian record is 36 years). They tolerate food shortages well and can endure several successive years of marginal feeding.
Skua (Great and Arctic): In Shetland colonies, the diet of great skuas is primarily fish, predominantly whitefish (discards), sandeel, and herring. In poor sandeel years, bird meat comprised a significant portion of its diet, with kittiwakes, puffins, and fulmars the most common prey. The bird appears to have altered its historic diet, because even during good sandeel years, skuas still consume an estimated 200,000 other birds.