Wednesday, October 17, 2012

Invasive Species in our local Waterways

Invasive Species in our local Waterways
By John Reinke

Several species of invasive amphibians, reptiles, mollusks and mammals have established themselves in King County's lakes, rivers and streams. his piece discusses the three species that I've observed in the Sammamish River.   It is almost a certainty that they can also be found in Bear Creek, which flows into the Sammamish River.

The three species are: Asian clam (Corbicula fluminea), American bullfrog (Lithobates catesbeianus), and the red-eared slider turtle (Trachemys scripta elegans)

credit: John Reinke
American Bullfrog
   The American bullfrog is native to the eastern United States, but has spread throughout the country. It is a voracious feeder, and will consume anything that can fit in its large mouth. Body length can be as long as six inches, with the legs adding as much as another ten inches. Very large bullfrogs can weigh almost two pounds.  I have seen and photographed them in and near the Sammamish River.

   It has proven easy to raise in ponds for commercial sale. Consequently, the species is now factory farmed in many parts of the world for food. According to the New York Times, more than two million bullfrogs are imported live into the San Francisco Bay Area every year. The problem is that they bring with them the deadly chytrid skin fungus, which has wiped out hundreds of frog species worldwide. (It is not harmful to humans.) A study of nearly 500 fresh-bought frogs from San Francisco, Los Angeles and New York found that 62 percent were infected with this fungus. A few manage to escape and thus help spread the fungus in the U.S.

   Locally, these bullfrogs outcompete (and also eat) native species, which are in decline partly as a result. Bullfrogs also consume ducklings, garter snakes, and even the native western pond turtle. That's why the King County environment website says: "If you catch one, feel free to eat it!"

Credit:  John Reinke
Red-eared Slider Turtle
   Like the American bullfrog, the red-eared slider is native to the eastern U.S. It is the most commonly sold pet turtle across the country. This has greatly contributed to its spread, as some escape into the wild and others are let go by owners who no longer want them.

   Their name comes from the distinctive red patch of skin around their ears. The "slider" part comes about from their ability to quickly  slide into the water from rocks and logs. Red-eared sliders eat a variety of animal and plant materials including fish, crayfish, tadpoles, snails, crickets, aquatic insects and numerous aquatic plants.

   Red-eared sliders have overwhelmed native western pond turtles to the extent that according to Wikipedia, the latter have not been found in the Puget Sound area since 2007.

Red-eared sliders should not be confused with painted turtles, which are also found around Puget Sound. The latter have bright red or orange red markings on the plastron (bottom of the shell) and undersides of the marginal scales of the carapace (the top of the shell). Painted turtles are not endangered. They are also an introduced species around Puget Sound, although they occur naturally in the eastern part of the state.

   During the summer, I frequently see red-eared sliders hauled out on rocks or logs along the Sammamish River in Redmond. They are very skittish and will usually quickly disappear when you approach them. The turtle you see in the accompanying photo was an exception, in that I was able to get fairly close to it before it splashed into the water. A very strange thing was that after I took the photo, I noticed that there is an Asian clam attached to what looks like a plant stem, just below and to the side of the turtle! I have no way to account for this.  Read More >>

Asian Clam
   Asian clams originate in Southeast Asia, where they are an edible food source. They were first discovered in the U.S. in 1938, along the Columbia River. Since then, they have spread to 38 states across the country. The clams have caused millions of dollars worth of damage to the power and water industries. Young clam larvae are carried by water currents into the intake pipes of these facilities, where they attach themselves by byssal threads. They then grow and eventually obstruct the flow of water to the point where expensive efforts are necessary to remove them. Their presence was recently discovered in Lake Whatcom, up by Bellingham.

   In July, it took me only ten or fifteen minutes to collect about 25 specimens (alive and dead) from the Sammamish River where it flows underneath the Leary Way Bridge in Redmond. The open dead shells were easy to spot along the bottom, and a little scooping up of gravel and sediment turned up several live ones. In other words, they are quite well established in the river.

   According to various reliable sources, Asian clams are preyed upon by fish, crayfish, raccoons, otters and even muskrats. Among the dead shells I collected were a few with what appeared to be small neat holes drilled through the shells into the interior.  I don't have any idea what type of animal would be capable of drilling these holes.

   Locally, the problem with these clams is that they can outcompete our native freshwater mussels, thus contributing to their elimination from our local environment. They can also increase the amount of phosphorus and decrease the amount of dissolved oxygen in the water.

Photos and Story by John Reinke
First published in the Water Tenders Fall, 2012 Newsletter

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