Aquarium Nursery Raises Endangered Frogs for Wild Release

In a nursery at the Aquarium of the Pacific in Long Beach, hundreds of critically endangered mountain yellow-legged frogs and tadpoles are raised under the care of conservationists before being released into the wild.

The species was once the most populous vertebrate in its mountain habitat, but its wild population had fallen to fewer than 200 by 2021. The aquarium last month marked the release of 1,000 frogs since 2020, the year the Bobcat Fire destroyed about 95% of the frog's habitat. More than 650 frogs were released in August, nearly 400 of them raised at the aquarium. Captive rearing and breeding efforts under the U.S. Fish and Wildlife Service began in the early 2000s.

"Although they're pretty slow growers, given the right conditions, frogs are pretty successful, so my hope is that we can get them back," said Erin Lundy, the aquarium's conservation initiatives manager.

The frogs play an important role in native ecosystems, serving as food for several animals and, as tadpoles, helping keep waterways clean by eating large amounts of algae and other decaying organic matter.

Their decline began in the late 1800s, when nonnative trout that preyed on tadpoles were introduced to their habitats for recreational fishing. Populations began to recover in areas where the trout were removed. The frogs are also susceptible to chytrid fungus, which has caused declines or extinctions among hundreds of amphibian species worldwide.

After the 2020 fire, rainfall turned burn areas into mudslides and filled waterways with runoff. Scientists salvaged a handful of tadpoles from the area, which the aquarium raised and released.

The aquarium oversees the tadpole-to-frog metamorphosis of hundreds of tadpoles sent from the Los Angeles and San Diego zoos, which bred them. Lundy recently received a shipment of nearly 500 tadpoles from the San Diego Zoo. Some were descended from frogs in the San Jacinto Mountains and others from the San Bernardino Mountains, and they were separated into two groups because of slight genetic differences.

"These guys look amazing," Lundy said. "These are really, really healthy tadpoles."

The tadpoles are fed four to five times a day and eat ravenously at this stage, Lundy said. Scientists spread a mixture of spirulina, fish food and calcium on small plates, letting the tadpoles graze as they would on algae-covered rocks in the wild. Some had already grown legs, their bodies wiggling as they swarmed the food.

In another tank, tiny frogs not yet ready for release had stacked themselves under a heat lamp, about two weeks out of water. Frogs become eligible for release once they have all four limbs and no tail. About 60% to 65% of the aquarium's tadpoles survive to that stage, a rate considered high.

Lundy and her team periodically change water flow rates in the tanks so the young frogs grow strong limbs and get used to swimming in different conditions. She feeds them live crickets and fruit flies, and has added beetles to better mimic their wild diet.

She once worried the frogs would not know how to fend for themselves after release. During one release, she watched a frog jump from its container, land on a rock and immediately eat a housefly it had never seen before. It turns out, a frog just knows how to be a frog.