Monday, December 3, 2012

Tenacious Trespasser #2: Bullfrog

They secretly slither, swim, hitchhike and crawl their way, often traveling thousands of miles over land and sea to invade our local rivers, lakes and streams.  Once they make themselves at home, these pesky invaders wreak havoc on the aquatic ecosystem and local economy.  Yes folks, we are talking about Aquatic Nuisance Species.  In the next few months we will introduce you to 10 tenacious trespassers that pose a threat to the native flora, fauna, and fishes of the Columbia River Basin.  Keep a close eye out for these critters because we need to send them packing for good!

American Bullfrog   (Lithobates catesbeianus)

What is it?

The bullfrog is the largest species of frog in the United States with males reaching 8 inches in length and weighing up to one pound.  They inhabit a variety of freshwater habitats including ponds, marshes, streams, and rivers; as well as man-made habitats such as canals and storm water ponds. 

FACTUnlike other frogs, bullfrogs spend most of their time in the water where they feed.
What does it look like?

Tadpoles are dark green with black dots and yellow bellies and are up to 6 inches long.  Adults are greenish to dark brown with dark spots and gold eyes.  They have an exposed eardrum (tympanum) which can be twice the size of their eye in males.  The bullfrog lacks the two parallel lines of raised glandular skin between the back and side found on native frogs.  Instead a fold of skin begins just behind the eye and extends to its ear.
FACT:  The BULLfrog is named after its distinct call which sounds like a cow mooing.

Where is it from & where it is now?

The bullfrog is native to the eastern United States and southern Quebec and Ontario.  It has been introduced to many areas of the western United States, Europe, South America, and Asia.

FACT:  The bullfrog can now be found in all of the lower 48 states.

How did it get here?

Bullfrogs were probably originally introduced accidentally during fish stocking into many lakes in western states.  They were intentionally introduced as a food item (frog legs) during the early 1900’s and have been widely distributed through the aquarium trade.
FACT:  Bullfrogs can travel up to a mile over land during wet seasons, allowing them to colonize new waters and expand their range.

What are its impacts?

Adult bullfrogs eat anything they can catch and swallow including native frogs, turtles, birds, fish, crustaceans, and bats.  Because they lack predators and have a high rate of reproduction, bullfrogs can quickly establish themselves in areas resulting in declines in native populations.  Bullfrogs have been blamed for the decline of the native Western pond turtle in Oregon, Washington and California. 
FACTBullfrogs lay up 20,000 eggs each season while native species such as red-legged frogs only lay up to 5,000 eggs.

What is being done about it?

Control measures such as regulated harvests, introducing predator species (e.g. largemouth bass), trapping and collection of egg masses have been used to combat this fiendish frog, but most methods are considered too expensive and time consuming.  Prevention through public education is considered the best, most effective measure to combat the spread of Bullfrog.  And remember, Washington State has classified the bullfrog as a Prohibited Aquatic Animal Species, meaning they may not be possessed, purchased, sold, propagated, transported, or released into state waters.
FACT:  In Oregon, the bullfrog is considered a controlled species and can be legally harvested year-round; no license is required.

How can YOU prevent the spread of bullfrogs?

  • NEVER release unwanted pet frogs or science projects into the wild.  Instead, consider giving it to a friend.
  • DO NOT purchase or share bullfrogs at any life stage (eggs to adults).  Report any bullfrogs you see for sale to Oregon Department of Fish and Wildlife or Washington Department of Fish and Wildlife.

Submitted by Donna Allard

1 comment:

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