Look out, Kermit! There’s a plague of invasive frogs and they’ve got big appetites.
American Bullfrogs (Lithobates catesbeiana) arrived in California at least 100 years ago and are now widespread. Bullfrogs eat just about anything, such as other frogs and bullfrogs, toads, snakes, turtles, birds and mice. In fact, California Department of Fish and Wildlife found a young coho salmon inside a bullfrog! And they’re blamed for causing the decline of native western red-legged and yellow-legged frogs by eating and outcompeting them.
In contrast, the bullfrog’s (really big!) tadpoles mostly eat algae and aquatic plants. Some fish, aquatic insects, garter snakes and wading birds eat the tadpoles. For more information on American Bullfrogs, visit University of Michigan Museum of Zoology’s Animal Diversity Website.
African Clawed Frogs (Xenopus laevis) were used worldwide for human pregnancy tests in laboratories during the 1940’s and 1950’s. When newer technology arrived, the frogs were released. Some that were kept as pets were released when owners no longer wanted them or they simply escaped from home aquaria. African clawed frogs can tolerate salinity, low oxygen, silt, pollution and both acidic and alkaline waters (pH 5-9). When ponds dry up in the summer, they can estivate in the mud for up to 8 months and can go without food for up to a year.
African clawed frogs can reach 5 inches long and they have claws on the three outer toes of their front legs. They are voracious and prefer aquatic insects, but they will eat fish, other amphibians (including their own kind), birds and even decaying debris. The African clawed frog can reproduce by the age of 6-10 months and a female can produce 27,000 eggs each season. Their ability to escape predators, secrete toxins and resist infections enables them to live up to 10-15 years in the wild.
Visit Columbia University's Website to learn more about African Clawed Frogs.
So, if these “ribbiting” invaders are already widespread, why are we writing about them? Their stories show how important it is to avoid releasing aquarium pets or schoolroom animals into the wild, where they can spread and harm native species.
Information on invasive frogs was included at a Spring 2013 workshop series for southern California public agency employees who work in aquatic habitats. The workshop was conducted by UC Cooperative Extension Advisors Leigh Johnson, Sabrina Drill and Darren Haver.
Getting the word out about especies invasoras acuáticas (aquatic invasive species) en Español is not just about translating English flyers and posters. For example the slogan, “Don’t Move a Mussel,” is catchy in English because it’s a play on words. The pun doesn’t work in Spanish. Myriam Grajales-Hall, News & Outreach in Spanish Program Manager for UC Division of Agriculture and Natural Resources, explains that English needs to be adapted, instead of translated, to Spanish. Adapting takes into account cultural differences and how each language is put together.
To address this challenge, UC Cooperative Extension Specialist Ted Grosholz and Advisors Jodi Cassell, Sabrina Drill, Leigh Johnson and Greg Giusti and California Sea Grant Extension Aquatic Resources Specialist Carolynn Culver teamed up with Grajales-Hall.
They held focus groups in northern and southern California during May and June 2013 to ask for advice from English- and Spanish-speaking boaters, anglers, kayakers, and staff of community organizations and the California Departments of Parks, Boating and Waterways, and Fish and Wildlife. The groups took a look at existing print materials and PSAs, gave their opinions on what else is needed, and suggested good ways to reach Spanish speakers who enjoy aquatic recreation.
The results are still being analyzed, but Grajales-Hall and her staff are already reaching out en Español. Click on these links to see their website article and YouTube video on especies invasoras acuáticas and their Facebook and Twitter pages en Español.
Renewable Resources Extension Act funding from US Department of Agriculture supported the focus group project.
The UPDATED Quagga and Zebra Mussel Eradication and Control Tactics Technical Report is now available from UCANR Coastal Resources and from California Sea Grant. This practical and well-researched 36-page report was developed to help lake, reservoir and irrigation district managers prepare for and implement eradication and control strategies for quagga and zebra mussels and other aquatic pests. The report was originally published in January 2013 and has been slightly revised to clarify a few items, add some photographs and update web links. Although most of the original material is unchanged, we encourage anyone who downloaded the original report to replace it with this June 2013 version. The new version can be distinguished by the close-up inset, photo of mussels shown below that has been added to the cover.
We would be delighted to hear from lake, reservoir and irrigation district managers who have used the manual. Are you willing to provide comments on how you have used the manual and the difference it has made? If so, please send an email to Leigh Johnson at firstname.lastname@example.org with the subject line: Mussel Control Manual Feedback and include in the body of the message: your name, organization and contact information. We'll follow up with a few questions. Thanks so much!
The manual explains how to use an Integrated Pest Management (IPM) approach and specific tactics for eradicating and/or controlling invasive dreissenid (quagga and zebra) mussels in lakes, reservoirs and irrigation canals. It covers how to develop and get started on a management strategy, manual and mechanical removal, oxygen deprivation, chemical application, emerging technologies, and an overview of permitting and regulatory processes. The report includes photos and diagrams, successful examples of eradication and control efforts that have used each of the tactics, and extensive weblinks to resources for more information.
It is based in part on presentations by experts at a joint workshop presented by Aquatic Resources Specialist Carolynn Culver of California Sea Grant Extension and by Coastal Resources Advisor Leigh Johnson and Natural Resources Advisor Jodi Cassell of University of California Cooperative Extension in San Diego on February 1-2, 2012.
People, weather and migrations move species to new locations all the time. Most newcomers (non-natives) settle in, get along with the natives and don’t interfere with human activities. In fact, some non-native species are brought in as biological controls for invasive species!
Species that become invasive can multiply fast. We may miss them when they are new and few. Some aquatic invasive plants can reproduce from a fragment and some animals can reproduce without a mate. Typically, invasive species can endure difficult environmental conditions, giving them an edge over other species.
Invasives cause problems when their populations boom. For example, waterweeds, such as Water Hyacinth, Hydrilla, Brazilian Egeria, Giant Salvinia and Spongeplant create dense mats on the surface of the water. They interfere with water flow, water delivery and navigation. The mats block sunlight, so algae in the water below cannot produce oxygen. The algae and animals in the water die and the decay process uses even more oxygen. The California State Parks’ Division of Boating and Waterways works to control waterweeds in the Sacramento-San Joaquin Delta.
Invasive species can out-compete native species for food and living space and some actually eat the natives. Quagga and Zebra Mussels, the Asian Clam and some species of Asian Carp (a catch-all term for several species of freshwater fish) out-compete other species by consuming large amounts of plankton (microscopic plants and animals). Other species of Asian Carp eat aquatic plants or small shellfish. The big, beautiful Apple Snail can decimate plants that native fish and birds need for food and shelter. Snapping Turtles, American Bullfrogs & African Clawed Frogs are voracious eaters of others and they can also out-compete for food and space. These two frogs and the Red-Eared Slider Turtle can carry disease to native animals.
Invasives that out-compete native species can cause problems up the food chain. For example, the Killer Seaweed (Caulerpa taxifolia) rapidly covers the seabed, crowding out other marine plants, because fish dislike it. Marine animals die or leave the area, because an inedible, green carpet has replaced their food. The New Zealand Mud Snail crowds out native snails, but tends to pass right through the digestive tracts of fish. The single-celled alga called Rock Snot (yuck!) or Didymo forms dense mats that smother cold-water streambeds, choking out native species that are food for trout and other fish.
Aquatic invasive species can also wreak havoc with our economic activities. The Red Swamp Crayfish and the Chinese Mitten Crab burrow in the mud, causing erosion in rice fields and levees. Quagga and Zebra Mussels and Asian Clams are probably best known for clogging water supply systems. Sharp mussel shells can cut fishing lines, anglers’ hands, and waders’ feet. Apple Snails are major pests in Asian rice fields and could pose a problem in California.
We’ll talk more in other blogs about some of these species, control programs, what you can do to alert authorities if you spot them, and how you can avoid spreading them.
This blog series is drawn from information presented in Spring 2013 workshops conducted by UC Cooperative Extension Advisors Leigh Johnson, Sabrina Drill and Darren Haver and from other reputable sources.
They’re not really invisible, but New Zealand Mud Snails (Potamopyrgus antipodarum) are so tiny you’d probably miss them in the mud on your boots. They can range from about 1/8 inch long to the size of a grain of sand. What’s the big deal about a tiny pest?
They multiply fast! In Yellowstone National Park they’re reported to be as dense as 100,000/square meter (83,613/square yard). In the United States all NZMS are females, who can reproduce without a mate.
They crowd out native species, such as mayflies, caddis flies and midges for food and space. NZMS is a poor replacement for native species as a food source for fish, because it provides little energy and may pass right through the fish’s digestive system. UC Santa Barbara has more information and scientific references on ecological impacts of NZMS.
In southern California NZMS are found near Pyramid Lake along I-5 and along the coast from Ventura to San Clemente. They’re also in the Central Valley, San Francisco Bay and Delta, and along the north coast. Check out USGS’s map of NZMS sightings. Expand and move it to see California locations.
Mud snails are tough. They can tolerate a range of temperatures, as well as silty and brackish water. When water flows fast, NZMS burrow into the mud to avoid being swept away. If the mud snail finds itself out of the water, it closes its operculum (shell door) until it’s back in the water. US Geological Survey has a fact sheet with more information on NZMS.
NZMS and the native Physa snail can occur together. The mud snail’s shell tapers gradually from mouth to peak. In contrast, the Physa’s shell is much wider near the mouth and it lacks an operculum. UC Santa Barbara has tips to help you distinguish NZMS from similar snails.
What can boaters, anglers, scientists and field staff do about NZMS? Inspect your boots, hem of your pants, vehicle tires, fishing and field gear, and so forth for mud, pondweeds, debris and snails. Also check float tubes, boats, trailers, and in fact anything that’s been in contact with the water or mud. In our workshops* for public works and parks staff in southern California, we mixed tiny beads into mud and they competed to see how many they could find. They saw first-hand how hard it is to spot tiny, gray to dark-brown NZMS.
Use a scrub brush to remove snails that you see and then rinse away any remaining mud, weeds or debris. It’s important to do this onsite, so you don’t carry mud snails (and other invasive species you may not notice) to another lake or stream. California Department of Fish and Wildlife recommends also freezing waders, boots, and other gear overnight (for at least 6 hours). If you have extra gear, keep one set to use only in infested waters. For more information visit the CDFW’s NZMS page.
In a future blog, we’ll tell you how to report a sighting of suspected New Zealand mud snails and other aquatic invasive species.
*UC Cooperative Extension Advisors Leigh Johnson, Sabrina Drill and Darren Haver trained 181 public works, watershed and parks staff in San Diego, Orange, Los Angeles and Ventura Counties on how to recognize and report aquatic invasive species and how to inspect and decontaminate gear and boats. This blog series is drawn from information used in these Spring 2013 workshops and other reputable sources.