Endangered Frogs Find Refuge in Los Angeles Aquarium Nursery

The Aquarium of the Pacific in Long Beach is playing a crucial role in the survival of the critically endangered mountain yellow-legged frog, nurturing hundreds of tadpoles and frogs in its specialized nursery before their release into the wild.

This conservation effort is vital as the species, once the most populous vertebrate in its mountain habitat, had dwindled to fewer than 200 individuals by 2021. The aquarium has celebrated releasing 1,000 frogs back into the wild since 2020, with more than 650 released in August alone, nearly 400 of which were raised at the facility.

Captive rearing and breeding programs for the mountain yellow-legged frog, supported by 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.

These frogs are essential to their native ecosystems. As adults, they serve as a food source for other animals, and in their tadpole stage, they contribute to waterway health by consuming algae and decaying organic matter.

Threats to the Mountain Yellow-Legged Frog

The frog's population decline began in the late 1800s with the introduction of nonnative trout to their habitats for recreational fishing. In areas where these trout were removed, the frog populations showed signs of recovery. Additionally, the species is highly susceptible to chytrid fungus, a pathogen that has devastated amphibian populations globally.

A significant blow to the mountain yellow-legged frog occurred in the fall of 2020 when the Bobcat Fire destroyed approximately 95% of its natural habitat. Subsequent rainfall exacerbated the situation, turning burn areas into mudslides and contaminating waterways with runoff. Scientists managed to salvage a small number of tadpoles from the affected region, which were then raised at the aquarium.

From Tadpole to Frog

The Aquarium of the Pacific receives hundreds of tadpoles from the Los Angeles and San Diego zoos, which are responsible for the initial breeding. Lundy described the arrival of nearly 500 tadpoles from the San Diego Zoo as exciting, noting that the tadpoles, some originating from the San Jacinto Mountains and others from the San Bernardino Mountains, were kept in separate groups due to minor genetic variations.

"These guys look amazing. These are really, really healthy tadpoles," Lundy said. At this developmental stage, the tadpoles are fed four to five times daily, consuming a mixture of spirulina, fish food, and calcium, mimicking their natural diet of algae-covered rocks.

The aquarium's care team meticulously manages the metamorphosis process. Tadpoles are housed in tanks where water flow rates are periodically adjusted to encourage the development of strong limbs, preparing them for life in varied aquatic conditions. They are also fed live crickets and fruit flies, with the occasional addition of beetles to further diversify their diet and simulate natural foraging.

Survival rates are high, with about 60% to 65% of the aquarium's tadpoles successfully reaching the stage where they have all four limbs and no tail, making them eligible for release. Despite the intensive care, Lundy expressed initial concerns about whether the frogs would adapt to the wild. However, observations during one release showed a frog immediately catching and eating a housefly, demonstrating an innate ability to survive in its natural environment. "It turns out, a frog just knows how to be a frog,” Lundy remarked.