Humans ship hundreds of millions of animals around the world each year, for pets, food, bait, lab research, and for use in zoos. Unfortunately, animals are often either purposely set free in their new environment, or they escape. Many of these invasive species adapt to their new environments, where they reproduce and become established. These species can predate upon native species, outcompete native species for food resources, and spread infectious diseases to native populations. Invasive species are one of the most serious threats to native wildlife worldwide, as they are incredibly difficult to eradicate from the wild once they become established. On top of driving native species to dangerously low numbers or to complete extinction, invasive species cost humans billions of dollars each year in environmental damage.
There is an urgent need to drastically reduce the intercontinental trade and transport of wildlife species involved in the pet trade, bait trade, and food trade, as these trades provide little benefit to humans, but cause immense damage to Earth's ecosystems, and are therefore unsustainable.
Bullfrogs are native to eastern North America. Unfortunately, they have been transported around the world for use as food, and have now become established in at least 15 countries, as well as throughout western North America. Being a large amphibian, they not only compete with native amphibians for food resources, but they are actually voracious consumers of any frog that can fit in their mouth!
After the early settlers of California ate unsustainable numbers of native California Red Legged Frog populations, the 1890's Californian entrepreneurs decided that bullfrogs would be needed to appease the appetites of these frog-loving gold miners, so they imported large numbers of bullfrogs from the Eastern USA, starting bullfrog farms and setting them loose in the wild where they have wreaked havoc on native frog populations ever since. To this day, bullfrogs eat native frogs, outcompete them for food, and spread infectious diseases like chytridiomycosis, which has driven 100 frog species to complete extinction.
How bad is the problem? Over 5 million bullfrogs get imported into San Francisco, Los Angeles and New York City each year, and a recent study demonstrated that 62% of these frogs are infected with the deadly chytrid fungus! Bullfrogs have become established in California, Oregon, Washington, British Columbia, Colorado, China, Colombia, Cuba, Dominican Republic, France, Haiti, Italy, Jamaica, Japan, Mexico, the Netherlands, Puerto Rico, South Korea, Taiwan, Venezuela and Uruguay. (Note: In March 2010 the California Fish & Game Commission discontinued the issuing of permits for the importation of non-native frogs for food. Thanks to the 1,196 SAVE THE FROGS! supporters who sent letters to the Commission urging them to take action on this issue!)
Did you know that pet shops throughout the western United States still legally sell bullfrog tadpoles? We're working on getting laws in place to ban the sales of these known invasive species outside their native range. You can see this proposal we have submitted to California State Senator Joe Simitian. Can you help us out by donating $20 so that we can institute these new laws as soon as possible? The choice is native frogs and healthy ecosystems, or a lot of big fat bullfrogs.
Bullfrogs eat endangered Coho Salmon.
Many of the world's high alpine lakes and streams are naturally fishless, as waterfalls have prevented fish from swimming to these regions. In the last century however, anglers, with the help of government agencies and fishing groups, have stocked several trout species into these naturally fishless areas. Small aircraft have been used to release baby trout by the hundreds of thoudands into some ponds in the high Sierra Nevada of California. This has caused huge problems for frogs like the Sierra Nevada Yellow-Legged Frog (Rana sierrae). Both brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) have caused problems for the endangered Spotted Treefrog (Litoria spenceri) in the mountains of Australia.
Frogs that co-evolve with fish may have toxic, distasteful tadpoles, may be camouflaged, may exhibit defensive schooling patterns, or may hide in reeds to avoid fish. But the Sierra Nevada Yellow-Legged frogs have no evolved defenses against fish. As trout are voracious predators of tadpoles, this frog species has been driven to extinction at nearly all ponds into which trout have become established.
The Sierra Nevada Yellow-Legged Frog was once the most abundant frog in California, but has now been extirpated from 92% of its historic localities. As the frog is also threatened by chytridiomycosis, and pesticides from California's Central Valley, this species is critically endangered, and its future remains uncertain. However, the Sierra Nevada Yellow-Legged Frog is still not listed by the United States government as an endangered species. This makes it incredibly difficult to protect the species, or to implement conservation strategies such as removing trout from the lakes to which they have been introduced, a method known to provide suitable habitat for the frogs.
Can you donate $20 to help us force the U.S. governement to classify the Sierra Nevada Yellow-Legged Frog as an endangered species, so that it receives the legal protections it requires?
Cane toads (Bufo marinus) are the world's most famous toad, and for good reason: they are masters of invasion. Native to Central and South America, they were introduced to numerous countries in the early 1900's. In 1935, 101 cane toads were taken from Hawaii (where they had been previously introduced) and were set free in the Townsville area of North Queensland, Australia, where it was hoped that the toad would combat the cane beetles (pests of the sugarcane). Unfortunately, the beetles are out by day and the toads come out at night. Further, the beetles live up high in the cane, and the toads are terrestrial. So the cane toads did not eat many beetles. They did however reproduce! A female cane toad can lay 20,000 eggs, and the cane toads were well adapted to the Australian environment, due to the toxins they hold in their paratoid gland. These toxins deter native wildlife from feeding on the toads, and the toads have taken full advantage of their freedom to wander the landscape virtually unscathed: there are now hundreds of millions of toads in Australia, and they are on an incessant march westward. They have now taken over a large portion of the top half of Australia, and are expanding their westward at a rate of about 50km per year.
Cane toads can grow very large, up to nearly a kilogram. To do this, they have to eat a lot of insects! This means they are competing for food resources with native Australian frogs, and this is likely a problem.
The Red Swamp Crayfish (Procambarus clarkii) is native to the southeastern United States. It is commonly used as bait by fishermen. Unfortunately, crayfish either escape or are intentionally released, and have become established in southern California, Spain and Portugal, where they are causing serious problems, as they have an appetite for newts and salamanders.
By Wildlife Biologist Mark Allaback
Although it has taken a decade and is (somewhat) ongoing, I believe I have been instrumental in eradicating bullfrogs after they were introduced to the Big Sur Watershed in 2000 at a California Red-Legged Frog (Rana draytonii) breeding pond. Of course, the bullfrog eradication effort required lots of work, including 2 pond drainings and endless hunting. But since there were no known bullfrog sources from the relatively isolated area, it was a worthwhile effort.
Unfortunately, we have also lost the California Red-Legged Frog breeding population from the site, almost certainly due to Louisiana Red Swamp Crayfish. Although present when I arrived in 2000, after draining the pond, they completely took over, effectively removing all submergent vegetative cover and presumably feasting on eggs and tadpoles (scattered detections of tiny numbers of late-stage tadpoles were nearly all hammered by pincers). The pond is perennial. Daily crayfish trapping does nothing, although 5000-6000 crayfish are removed each year.
This year we may essentially take the pond out of commission, at least half the year, by dewatering in late May and keeping it dry until the rains begin in Oct. Perhaps if we do this, the crayfish reproductive cycle will break, and Red-Legged Frogs will one day re-colonize. However, Red-Legged Frogs have not bred successfully since about 2002, although they attempted to for many years (egg mass counts have dropped from ~45 in 2004 to 1 this year).
The crayfish burrow but maybe reducing the hydro-period to 6-7 months for 1 or more years will take them out. My fear is that they will return, since I have seen them disperse overland and found them under debris far from water.
The mosquitofish (Gambusia holbrookii and Gambusia affinis) is often introduced into backyard ponds by homeowners, and into larger waterbodies by local governments attempting to control mosquito populations. Mosquitofish are known predators of native frogs and newts in California, and are also a problem for native frogs in Australia. Mosquitofish photo by S. Curtis.
Defenders of Wildlife wrote an excellent report in 2008 entitled Broken Screens.
If you'd like to learn more about invasive amphibians and reptiles, have a look at Fred Kraus' book 'Alien Reptiles and Amphibians: a scientific compendium and analysis'.