Why 5,000 Tadpoles Were Shipped From Nashville to Puerto Rico

It's an example of long-distance conservation.

Puerto Rican crested toad tadpoles
Puerto Rican crested toad tadpoles are smaller than peas.

Kate Johns / Nashville Zoo

A special care package is on its way from Nashville to Puerto Rico. More than 5,000 tadpoles have been shipped to be released into their native habitat.

The tadpoles are Puerto Rican crested toads, the only toad native to Puerto Rico. They’re listed as endangered by the International Union for Conservation of Nature (IUCN) with their population numbers decreasing. There are only an estimated 1,000 to 3,000 of the animals left in the wild in the Guanica State Forest in the southwest part of the island.

Because of its perilous position, the Puerto Rican crested toad was the first amphibian placed on a Species Survival Plan (SSP). That’s a program developed by the American Zoo and Aquarium Association (AZA) to help ensure the survival of threatened or endangered species in captivity.

The plan was created in 1984 with a handful of zoos participating. Now 20 zoos take part, including the Nashville Zoo. Since the program’s inception, 263,575 tadpoles bred at zoos and aquariums throughout North America have been released into protection ponds in the Guanica State Forest.

The Nashville Zoo has been working with the Puerto Rican crested toads since 2008 and was first successful at breeding them in 2012. To date, the zoo has sent more than 21,000 tadpoles to Puerto Rico to be released.

“All the participating AZA institutions that are selected for a certain release follow a specific protocol for cooling and placing the toads in the rain chamber to stimulate breeding,” Sherri Riensch, lead herpetology keeper at Nashville Zoo, tells Treehugger. “This allows for all of the tadpoles to be the same age and size upon release thus none of the different genetics will have a leg up on any of the others.” 

Puerto Rican crested toad
The species is known for its crested head. R. Andrew Odum / Getty Images

Puerto Rican crested toads are known for their distinctive bony head crest. They can range in color from yellow-green to brown-black on top with a creamy white underside. They are medium-sized, with adults reaching between 2.5 to 4.5 inches (6–11 centimeters).

Handling with Care

Nashville Zoo employees package tadpoles
Nashville Zoo employees prepare tadpoles for shipping. Kate Johns / Nashville Zoo

The tadpoles are carefully packaged for their 1,700-mile trek.

“They are shipped like fish, in large plastic bags with clean water and oxygen added. The bags are placed in foam boxes inside cardboard boxes to insulate them from extreme temperatures and rough handling,” Riensch says.

“The tadpoles are small, less than the size of a pea when we ship them which allows us to put several hundred per box.”

When they arrive, the tadpoles are released in their native habitat. They are monitored by the U.S. Fish and Wildlife Service and the Puerto Rico Department of Natural and Environmental Resources (DNER) until they metamorphose and move on from the pond where they were released.

In some instances in the past, schoolchildren have taken part in the tadpole release as part of a local initiative to educate citizens on Puerto Rican crested toad conservation.

While this latest batch of tadpoles makes its way south to new ponds, the Nashville Zoo and other zoos across the country will be working on replenishing the habitat with more upcoming shipments.

“There are lots of different factors affecting threatened and endangered species across the globe. The local community doesn't always have the expertise, time, money, or space to be able to hold and breed a struggling species while the problems facing them—habitat loss, pollution, disease, and invasive species—are fixed,” Riensch says.

“The Nashville Zoo is just one of the many zoos and aquariums across the country working with these species and it is just one example of the conservation we are a part of both in our backyard and across the planet.”

View Article Sources
  1. "Species Information." Nashville Zoo.

  2. "Puerto Rican Crested Toad." IUCN Red List, 2020, doi:10.2305/iucn.uk.2021-1.rlts.t54345a172692429.en

  3. "About." Puerto Rican Crested Toad Conservancy.

  4. Sherri Riensch, lead herpetology keeper at Nashville Zoo

  5. "Puerto Rican Crested Toad." U.S Fish and Wildlife Service.