It’s a frog-eat-frog world: Local amphibians face tough
challenges that could signal changes ahead for humans
By Colleen Valles, Special to the South Valley Newspapers
Outsiders moving in; no more places available for living in; the danger of getting attacked; the spread of disease.
It’s the story of a changing neighborhood, but not the kind you might think. It’s what’s happening to South Valley’s native amphibian population. From those with colorful names to singing frogs, amphibians have been plentiful in southern Santa Clara County and San Benito County. But that diversity, like the diversity of amphibians the world over, is decreasing rapidly.
“The sensitive species, which a lot of amphibians are thought to be, are in short supply,” said Jae Abel, a biologist with the Santa Clara Valley Water District. “We have a couple of listed species – the California red-legged frog and the California tiger salamander – and they’ve largely been chased out of the valley bottoms where humans like to live.”
South Valley is home to a variety of amphibians, including the Western chorus frog, which is a tree frog that’s often heard on movie soundtracks; the Western toad; and the foothill yellow-legged frog, among others. The California red-legged frog and California tiger salamander are on the federal government’s threatened-species list, and the foothill yellow-legged frog is on the federal species-of-concern list, meaning the populations of all these animals has decreased significantly through the past several decades. In some areas, the populations have been wiped out altogether.
Amphibians are considered sensitive because of their very permeable skin, which makes it easier for them to absorb any pollution that is in the environment. For that reason, they’re considered a sentinel species, like a canary in a coal mine.
“Amphibians are one of the latest groups of organisms to show us changes are afoot on the landscape,” Abel said. “They’re susceptible to a lot of things that would be good for us to pay attention to. If you’re losing them, you start to look at why. Is the landscape changing, and for what reasons? And are those reasons going to affect us, too?”
Voracious Intruders
In the South Valley, the reasons for the amphibians’ decline are numerous. One of them is the introduction of species that aren’t native to the area. In the case of local amphibians, a major culprit is the bullfrog, which eats other frogs’ larvae.
Gold miners, who enjoyed eating frogs, brought bullfrogs to California in the 1800s to raise for food, said Kevan Urquhart, the Central Coast regions’ fisheries supervisor for the state Department of Fish and Game. Some of those frogs managed to escape and reproduce in the wild.
“Bullfrogs are better at surviving in disturbed and degraded habitats than the native fauna,” Urquhart said. Often, the native species get eaten, and the non-native species flourish.
The mosquito fish is another threatening outsider. The fish, a North African import, eats more than just mosquitoes; it also has been known to bite the legs off juvenile amphibians. A legless amphibian doesn’t stand much of a chance of survival.
Non-native species aren’t the only predation threat to amphibians. With humans and their trash come what are known as “subsidized predators” – animals such as raccoons, skunks, ravens and crows that feed on what humans leave behind. With more food to sustain their populations, the numbers of these predators, which also feed on frogs and salamanders, increases, and the numbers of amphibians can decrease.
Habitat Destruction
The disturbed habitats Urquhart mentioned – habitats that have dried out or have been completely lost – are another reason native frogs, salamanders and others are having a hard time hanging on.
When a community is developed, much of the land is paved for roads, basketball courts, patios and other features, a practice known as “hardscaping.” Hardscaped areas don’t absorb rainwater anymore; instead it is sent gushing into nearby waterways. That means there’s very little reserved water when the rainy season passes, making things tough on the critters.
“Because the (rain)water doesn’t percolate in, the creeks dry up in summer and fall. So urban development starves creeks of water in fall and summer and causes above-normal flows in winter. All this wipes out aquatic resources in the area,” Urquhart said.
But, he added, developments can be designed to maintain a waterway, and some are, but it’s something that developers need to plan for.
“If you don’t try to do it from the start, you wipe out the creek,” he said.
Another problem is the extraction of water from waterways and the ground to support communities.
“The more people you have in an area, the more straws you have sucking on a water supply, and it is scarce,” said Patricia Anderson, an associate fisheries biologist with the state Department of Fish and Game’s Resource Assessment Program. “The constant changes in the hydrology of the area – it’s happening way too fast in the Gilroy/Hollister area.”
Some native amphibians, such as tree frogs, are holding their own against the drying out and destruction of habitat. These frogs have a short reproductive time, allowing them to be successful in places where there’s a short wet period.
“They have a sort of opportunistic component to their life history pattern that’s much more flexible than others,” Abel said.
Disease
Those amphibians that don’t have an opportunistic component find their numbers weakened by habitat loss and predation, as well as disease. One of the most common disease-causing agents that biologists are worried about is the chytrid fungus, which appears on amphibians’ skin, through which they breathe.
Fungal and viral transfers are a real concern, Urquhart said, so those out in waterways looking to study the bodies of water or the organisms that live in them are taking care to clean their gear and boots to prevent the spread of disease. However, others are unaware of the dangers they could pose to amphibians simply by walking around their habitats.
What’s Being Done
With assaults on all sides, local amphibians are in need of humans’ help. Efforts are being made to protect those that have received federal or state recognition as species in trouble.
When builders find a species that is endangered or threatened, or when county planners see on maps that an area proposed for development is habitat for a listed species, the developer may have to take measures to mitigate the effect on the species. Those measures could include things such as moving the building site to another part of the parcel of land, said Colleen Oda, a Santa Clara County planner.
When a sensitive species is found on a proposed building site, the actions and requirements the county has for developers are largely dictated by state and federal law, said Art Henriques, director of planning and building services for San Benito County.
“If you have a site that’s obviously habitat, the requirements and protocols go up,” he said. “We are trying to make sure we are following the requirements and practices of the state Fish and Game Department.”
Santa Clara County and other counties around the state have gone further and have adopted or are working on developing habitat conservation plans. These plans aim to head off any disagreements between builders and regulators on how best to mitigate the environmental impacts of development.
The plans in Santa Clara County are expected to identify county land that is considered critical habitat for the listed species and set it aside for species preservation. The county is also expected to determine clear requirements for developers in order for them to build. The county expects to approve the plan in early 2009.
“A (habitat conservation plan) is a highly technical product involving a lot of biological and land-use issues and interrelating them,” said Ken Schreiber, HCP/Natural Community Conservation Plan program manager for the county. “We are under way, but there’s a good way to go yet. The current schedule seems like a long time, but is actually very ambitious.”
In the meantime, county, state and federal governments, and nonprofit organizations are working to lessen the impact on amphibians.
The Santa Clara Valley Water District has a wetland development project that itself poses unique challenges in trying to help local amphibians.
“When you’re trying to recreate habitat, you do it in hopes the amphibians can use it, and you have to manage it in hopes you keep the bullfrog from being successful,” said Don Arnold, ecological services unit manager for the Water District.
One of the best ways to protect the amphibians is to buy up large tracts of land, Anderson said. That helps keep habitats connected, so when species are on the move, they have a safe way to go from one area to another. The state Department of Fish and Game works with such organizations as the Nature Conservancy to acquire land.
Still, once the amphibians have taken a hit, it’s tough for them to get back on their webbed feet.
“One of the problems these things face is they’re in low numbers and scattered about in pockets, and if you lose a pocket, their ability to recolonize that spot is difficult. It’s looking kind of grim in many respects for the amphibians,” said Abel, the Water District biologist.
That grim future could be the catalyst to change course toward a more balanced use of land, Abel said. But, he added, “that’s a nice argument, but the practicality of the numbers of people on the planet is the bottom line. You have to find a place for all the people.”
South Valley’s Native Amphibian Population
The area covering southern Santa Clara County and San Benito County has been rich in amphibians. Some of the native species include:
– California Red-legged Frog: Rana aurora draytonii
– Foothill Yellow-legged Frog: Rana boylii
– California Tiger Salamander: Ambystoma californiense
