California Red-Legged Frogs Make List of Most Threatened

As a nod to leap day a few days ago, I decided to continue the frog theme for this week’s post by discussing the trials and tribulations of the California red-legged frog. This frog, whose scientific name is Rana draytonii, is the largest native frog in the western United States. According to the Center for Biological Diversity, it is also one of the top ten most threatened frogs in the country, having lost 90 percent of its historic population.

ARKive – California red-legged frog photo – Rana draytonii – G106304

The National Wildlife Federation lists four main reasons for the frogs’ decline:

• Disease
•  Invasive predators
• Habitat destruction
• Contamination of freshwater habitats

Disease

Amphibian populations around the world have been falling victim to a fungal disease called chytridiomycosis, and the California red-legged frog is no exception. The spores of the fungus burrow into the skin of frogs and other amphibians while they are swimming. As the fungus spreads, it prevents the skin from transporting nutrients necessary for the heart to function, killing the amphibian. According to the Biodiversity Group, this disease causes more than half of local amphibian species to become locally extinct within six months in any area that it strikes. Any amphibian species remaining only retains about 20 percent of its former population levels.

Frog infected by chytrid fungus (By: Forrest Grem, Source: wikipedia.org)

Invasive Predators

Predators that have been introduced to California from other parts of the U.S. have been detrimental to the red-legged frog population. Invasive species include the crayfish, mosquitofish, and the American bullfrog. While all of these predators eat large amounts of the California red-legged frog, the American bullfrog causes the most damage. Native to the eastern U.S., bullfrogs were introduced throughout the western states to help supply the frog leg industry in these states. In addition, the American bullfrog acts as a carrier for chytrid fungus because it is resistant to the disease.

Habitat Destruction

Save the Frogs, American’s only public charity dedicated to amphibian conservation, estimates that 95 percent of California’s coastal wetlands have been destroyed or damaged. This has had severe consequences for the endangered red-legged frog.

Protecting California red-legged frog habitat has been an ongoing struggle. In 2007, the Center for Biological Diversity sued the U.S. Fish & Wildlife Service for designating only 450,288 acres of habitat for the frog in a decision that bowed to corporate interests and ignored scientific evidence. The U.S. Fish & Wildlife Service responded by increasing the protected habitat to 1.6 million acres. This was a great victory for wildlife conservation, but efforts to protect the red-legged frog have not been as fruitful as hoped.

A current example of habitat destruction is the development of California’s Sharp Park Wetlands, an important habitat for the red-legged frogs. The mayor of San Francisco vetoed legislation to protect the wetlands opting instead to approve the construction of a golf course. As San Francisco pumps water out of the wetlands every year, tadpoles are sucked out to sea, and large egg masses are left on the ground to dry out. Because the red-legged frogs are endangered, killing them is a violation of state and federal laws, including the Endangered Species Act. Save the Frogs has created a petition to stop the wetland draining, but only 3,109 people have signed so far.

Contamination of Freshwater Habitats

Despite the acreage set aside in 2007 to protect California red-legged frogs, they are still in danger because pesticides and other chemicals have contaminated their habitats. In 2002, the Center for Biological Diversity filed a lawsuit to force the Environmental Protection Agency to ensure that chemicals registered by the U.S. Fish & Wildlife Service would not be detrimental to the red-legged frog. In 2006, these agencies developed a list of 66 harmful pesticides that could not be used in or near California red-legged frog habitats. Unfortunately, the EPA and the U.S. Fish & Wildlife Service failed to uphold the agreement. The Center for Biological Diversity sued again in 2011, and the litigation is still ongoing.

What can you do to help?

• Sign the petition asking San Francisco’s mayor to uphold the Endangered Species Act and stop draining Sharp Park Wetlands.
• Spread the word that non-native species should not be released into the wild.
• Do not buy amphibians as pets. This encourages the pet trade, which depletes natural populations, introduces invasive species to new areas, and can lead to the spread of disease.
• Support the protection of your local wetlands to help amphibians and other wildlife in general. (This includes allowing wetlands to follow their own natural cycles of moisture and drying).
• To learn more about the importance of frogs and amphibians, please read my previous post “Why should we care about the global amphibian decline?”

Thanks for reading! Please let me know why amphibians are important to you in the comments.