Sunday, September 1, 2013
Here are just a few of the shots I got of a Great Cormorant eating an American Eel in the Washington Channel of the Potomac River here in Washington, D.C. You can see all 15 shots here.
The Great Cormorant is a large seabird with an extensive range across North America, Europe, Australia, and Asia. It only weighs about three to five pounds, but it has a wingspan of four to five feet! The Great Cormorant is the largest of all cormorants, and is usually black colored with a yellow or dun throat. Great Cormorants vary widely in color, however, and it is not unusual to see them in brown, mottled brown, or grey.
The Great Cormorant is a diving bird, and in fact goes to great depths in lakes, rivers, and the ocean. Dives times of 20 to 30 seconds are not uncommon. It brings its prey to the surface, where it uses its hooked beak to manipulate it into position and then swallow it whole. Cormorants feed on fish, including eels.
Cormorants were once hunted almost to extinction, because fishermen felt that they competed for fish. But that stopped a few decades ago, and now there are maybe 1.6 million cormorants in Europe, as many in North America, and twice that number in Asia and Australia.
The American eel is one of the most widely spread eels in the world. Its habitat ranges from Mississippi on the Gulf Coast, around Florida, and up the East Coast of the United States and Canada as far north as Nova Scotia. Eels are fish, and although they have tiny scales they are covered in mucous that makes them look naked like a snake. They are somewhat vertical than round, and have a fin along the spine. Like snakes, they wiggle back and forth through the water to swim, using their tiny front fins for stability. American eels are generally dark green to greenish-grey, with lighter colors in clearer water. American eels spend most of their lives in fresh water -- rivers, inlets, creeks, and streams. They travel into the ocean to breed, heading for the Sargasso Sea. The female lays up to 4 million eggs in the seaweed, then dies. The hatchlings spend seven to 12 months in the seaweed, and once they are bigger they move toward the shore. Because they are still transparent (their skin has no color), they are known as "glass eels". They continue feeding, mostly on insect larvae, for about two months as they adjust from saltwater to fresh water. Once the eels reach the coast, they move into rivers and streams and take on a yellow-green color, during which time they are known as "elvers". This takes another three to 12 months, and many eels spend this time migrating far upstream. Once they reach "home" (wherever that is), they start changing color and become known as "yellow eels". During this stage, eels take on a sex (male or female). They begin preying on small fis, clams and oysters, crabs and crawfish, insects, worms, frogs, and plants. The final stage of adulthood is the "silver eel" stage, which the eel reachs just before it is ready to spawn. It lasts a few months, as the eel moves downstream to the ocean. Then it dies. Eels can live anywhere from six to 30 years!
American eels are mostly active at night. During the day, they hide in the mud near the shore. Eel populations are in decline all along the East Coast. This is partly due to pollution, and partly due to a loss of the small fish that eels feeds on during the elver and yellow eels stages of their life. Dams significantly disrupt their life cycle, because they cannot use fish ladders. They don't handle low-oxygen water well, but a lot of water in rivers and streams has low oxygen because of dams.
Cormorants are well-known to eat eels. But are eels a big part of their diet? We don't know. We see cormorants eating eels a lot, but that's because the eel writhes around a lot and the cormorant has to shake it (to stun and subdue it) at the surface, then get the eel into position (head down) so that the cormorant can eat it. This takes a minute or so. Fish, crustaceans, and then like doing fight back as much, aren't slimy, and are easier to get down in one gulp. So maybe we just don't see cormorants gulping down fish because they do it so fast.
Anyway, it was cool to see this Great Cormorant eating an American eel. The Potomac River is so polluted, seeing eels there is a big deal.