The bullfrog (Lithobates catesbeianus) is a large frog native to eastern North America. Its average size is in the range of 100-175 mm, and it can weigh up to 600 grams. It usually inhabits large permanent bodies of water, such as swamps, ponds and lakes. The bullfrog gets its name from the sound the male makes during the breeding season, which sounds similar to a bellowing bull. The use of this frog as a food source has led to bullfrogs being distributed worldwide outside of their native range.

Bullfrog control program in the mediterranean region of Baja California

Bullfrog. Photo by A. Soriano.

Currently, they have been introduced almost everywhere in the world, so outside their natural range, they are considered a species with a high impact on biodiversity because they can eat any animal that fits in their mouths, for example, birds, mice, snakes, turtles, frogs, crustaceans and insects. Because of this, it is considered one of the 100 most invasive and ecologically damaging species in the world.

The first record of bullfrogs in Mexico dates back to 1953. During the period 1945-1950, the importation of adult individuals of this species was formally established in order to establish farms (ranicultivos) for human consumption. Since then, this species has spread throughout the country. In 2022, 20 states had registered the presence of bullfrogs.

In Baja California, Fauna del Noroeste has identified 20 localities with bullfrog presence, representing 66% of the wetlands in the region. This figure could increase over time if bullfrog control and management actions are not carried out.

Photo by Rebecca Hughes Sabac.

How to identify it?

In 2017 we initiated the bullfrog control program, which aims to eliminate threats that directly affect native species, and in the long term restore Baja California's wetlands. This program is divided into four stages: 1) mapping and selection of pilot eradication sites, 2) eradication at pilot sites, 3) eradication throughout the distribution, and 4) monitoring.

In 2018 we started with mapping to locate sites with bullfrog presence. We conducted the review of historical sites with bullfrog presence and surrounding sites with permanent water presence. At this stage, 11 localities with bullfrog presence were identified, and after conducting the monitoring it increased to 17 localities showing an increase of 55%.

Photo by Selene González

Eleven variables were also obtained that allowed us to construct the bullfrog eradication indicator. This indicator shows the sites with the greatest possibility of achieving eradication. With these values, Rancho Madrigal, located in the city of Ensenada, was selected as the pilot site to begin bullfrog eradication.

In 2019 and 2020 we will continue with the second stage at Rancho Madrigal. Before, during and after the eradication, native fauna sampling was conducted to document the existing impact of the bullfrog presence, as well as to document the changes after eliminating the bullfrog from this location.

In 2020-2021 we are working on the third stage. The eradication of bullfrogs in the locality of La Misión, and El Salto in Baja California. These locations were selected based on the bullfrog eradication index. To date we have managed to eliminate 121 frogs of different ages. We hope that in the future our efforts will be reflected in the increase of native species.

This project has been made possible thanks to funding from N-Gen (Sonoran Desert Researchers Network), JiJi Foundation, National Geographic Society, Rufford Foundation, and collaboration with The Wildlife Project and the Sonoma Mountain Ranch Preservation Foundation.

La Misión. Photo by Andrea Navarro.

El Salto. Photo by Andrea Navarro.

How can you help?

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Although we have managed to eradicate this invasive species from one of the sites and are working on two other sites, throughout this project we have seen the increase of this and other exotic species in sites where they were not previously present. We can all do our part to prevent exotic species from spreading and damaging ecosystems and their native species.

Avoid removing and moving these organisms to other sites.
Do not release animals outside their natural range.
Avoid buying exotic animals from other parts of the world.
Do not introduce animals or plants into the country without knowing what species they are and their characteristics.
If you have a terrarium or aquarium pet and no longer want it, never release it in natural places in the region.
Inform yourself and others about introduced species.

If you would like to collaborate, volunteer or just want to know more, contact us at info@faunadelnoroeste.org, or through Facebook @Faunadelnoroeste.

If you want to know more about exotic species you can visit CONABIO's webpage: https://www.biodiversidad.gob.mx/invasoras

Help us in this project by reporting a sighting of this species by registering it on the Naturalista platform.