Amphibian Conservation: Crawfish Frogs in Crisis

What is the best way to repurpose a basement in one of the buildings at the Detroit Zoo? Turn it into an amphibian’s paradise!

Amphibians across the globe are in crisis, with populations declining rapidly due to climate change, habitat destruction and a disease called the chytrid fungus. In an effort to reverse this trend for the crawfish frog (Lithobates areolatus), which is listed as Endangered in the state of Indiana, the Detroit Zoological Society (DZS) partnered with the U.S. Fish and Wildlife Service, the Department of Natural Resources and staff at Indiana University. In 2013 these entities began a repatriation project, which is an effort to return a species to its natural habitat. This involved the collection of egg masses from grasslands in Indiana, which were then transported to the Detroit Zoo, where staff raised them until they were almost froglets before releasing them back into the wild.

The crawfish frog can lay egg masses with as many as 5,000 eggs. That might make one wonder how these animals could be endangered, right? Well, even if all of those eggs hatched into tadpoles, less than one percent of those tadpoles would ever make it out of the water. Tadpoles are an easy prey for a wide variety of animals including birds, fish, mammals, frogs and even larger tadpoles. And even fewer tadpoles would make it far enough into adulthood to breed. This shows how vulnerable the tadpole stage is in a frog’s life, which is why we focused our efforts on this stage.

We knew what we needed to do, but where is there enough room for thousands of tadpoles at the Detroit Zoo? How about right under the noses of Jasiri and Tamba, two Southern white rhinos! Not directly under them, since 12,000 pounds of rhino would be harmful to a tadpole, but rather in the basement of their indoor habitat. It took a lot of hard work from staff, but the space was eventually turned into a fantastic temporary home for crawfish frog tadpoles. Some of their luxury items include manufactured ponds with an automatic rain system, spotlights and temperature control systems – and of course, plenty of food.

In April, the crawfish frog egg mass is transported from Indiana to the Detroit Zoo in a cooler. We take this egg mass right down to the basement where it is placed in water. In a couple of weeks, tadpoles start to emerge, which are then counted and moved into long pond-like pools. We raise these newly hatched tadpoles for about three months, with the amphibian department staff feeding and cleaning them daily. It takes hours to care for the tadpoles each day, but it is all worth it in the end when they are driven back to Indiana and released. The total number of tadpoles varies from year to year, but since this project started in 2013, the DZS has released a total of 10,411 tadpoles back into the wild.

While wild tadpoles have less than a one percent chance of survivability, we were able raise that to an astounding 99 percent in 2014 and 2015 for these “basement” tadpoles. That’s because they don’t need to worry about predators, disease, lack of food or pollution. This lets them get a good head start on life – but we don’t make it too easy for them. Otherwise, they wouldn’t know what to do once they got back to the wild. So before they fully metamorphose – or turn into frogs – they are taken back to Indiana and released into the ponds. Since some frogs lead a “double life” – aquatic and terrestrial – they are able to finish their aquatic life stage in enclosed repatariums, or screened-in containers, that allow protection before they are released as full frogs in the environment in which they will live. This method works well and provides exposure to the environment they will be living in before they become too accustomed to the luxury of the rhino basement.

The DZS crawfish frog conservation project requires long hours, but it is also the best time of the year as a member of the amphibian department staff. Seeing how the DZS can make a positive impact on this species and the ecosystem is very rewarding.

– Michael Andrus is an amphibian department zookeeper for the Detroit Zoological Society and works in the National Amphibian Conservation Center at the Detroit Zoo.

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