Introduced species no welcome guests in Surf City ecosystem

VIC LEIPZIG AND LOU MURRAY

Vic’s career as a biology and birding instructor and my current job

as restoration coordinator of Shipley Nature Center often dovetail

nicely. That happened last week.

The neat thing about working at Shipley Nature Center is that

there is always some interesting natural sight that I can share with

Vic. Sometimes it’s a sad sight, such as the dead juvenile pelican I

found a few weeks ago in the meadow by Blackbird Pond. The youngster

was probably one of the many pelicans dying of starvation off our

coast. Even though the ocean is filled with their favorite food,

anchovies, these gangly birds are dying in record numbers, and no one

knows why. This bird was just one more victim.

Sometimes what I see at the nature center is endearing, such as

the two 5-month-old coyote pups playing near their den in the

mulefat, or the bunnies and ground squirrels that scamper all over

the place.

Last week, I found three little frogs in an irrigation ditch. Our

Orange County Conservation Corps work crew had dug a channel to

extend an existing irrigation line to make our watering chores

easier. During installation of the gate valve, some water had leaked

into the ditch. The mud made the ditch attractive to the frogs. But

at only an inch in length, the young frogs were too little to hop

back out.

The kids on the work crew caught the frogs so we could release

them in the pond, but then I noticed the frogs had claws on their

hind feet. Our native frogs don’t have claws. I suspected they were

African clawed frogs (Zenopus laevis), an invasive, introduced

species. I put the frogs in a bucket with a little water until I

could get someone to confirm or refute my identification.

The guys from Orange County Vector Control came by later that

morning to spray for mosquitoes. They told me that African clawed

frogs like the ones in my bucket had been in the area for decades.

This is the species that was used in the old frog tests to confirm

human pregnancies in the 1940s and 1950s. When more modern methods

came along, the frogs were released to the wild.

Other potential sources were the release of pet frogs. The

cuteness and hardiness of these plump-bodied, small-headed frogs made

them suitable for the pet trade until society wised up to the fact

that more and more introduced species were wiping out native

wildlife.

In Southern California, competition from African clawed frogs is

one of the factors responsible for the decline of our native

red-legged frogs. Actually, it’s more than competition. African

clawed frogs, which are up to 5 inches in length, will eat red-legged

frogs. They compete with and consume native fish as well.

I took the three frogs home to Vic. Naturally, he was very

appreciative of my gift, but he pointed out that I had violated two

state laws. It is illegal to possess African clawed frogs or to

transport them. He kept the frogs long enough to show them to his

biology class, then dispatched the alien amphibians.

We know African clawed frogs have been in Central Park since at

least the early 1970s, because we found a booklet from the 1974

Central Park dedication that mentioned them. The frogs are now

widespread throughout local flood-control channels.

Biologists from the California Department of Fish and Game have

tried poisoning infested ponds with rotenone. Everything in the pond

was killed except the African clawed frogs, which hopped away. They

are more capable than other frog species of crossing land to get to

another body of water. California fish and game has tried drying up

ponds, but the African clawed frogs just burrow into the mud, where

they can survive for nine months without water. The department even

tried blowing up the frogs with detonator cords, but that too failed.

The African clawed frog is one more example of an introduced

species that can decimate local, native species.

This is happening all over the world. A handful of species, helped

along one way or another by the actions of humans, spread at the

expense of species that people don’t help.

Blackbird Pond is simply a microcosm of what is happening on a

global level. This Southern California coastal freshwater pond should

have Pacific tree frogs, Western toads, slender salamanders and

Western pond turtles. It doesn’t. Instead it has bullfrogs, African

clawed frogs, red-eared sliders and a soft-shelled tortoise -- all

introduced species. Someone sneaked a large snapping turtle into

Blackbird Pond last year. We haven’t seen the Western pond turtles

since.

People mean well when they release their pets back to the wild,

but they don’t think about whether those animals really belong in the

ecosystem in which they released them. The result of these deliberate

releases is ecological disaster. It’s not a pretty sight.