Landmark Study Reveals Low National Rate Of Frog Abnormalities On Wildlife Refuges

Tuesday, November 19, 2013

An unprecedented 10-year-study by the U.S. Fish and Wildlife Service shows encouraging results for frogs and toads on national wildlife refuges. The study, published Tuesday in the peer-reviewed online journal PLOS ONE, finds that on average, less than two percent of frogs and toads sampled on 152 refuges had physical abnormalities involving the skeleton and eyes – a lower rate than many experts feared based on earlier reports.  This indicates that the severe malformations such as missing or extra limbs repeatedly reported in the media during the mid-1990s were actually very rare on national wildlife refuges.

“Frogs and toads are strong indicators of wetland and environmental quality. What affects them affects a broad range of other species,” said Service Director Dan Ashe. “This research significantly advances our understanding of amphibian abnormalities while amassing one of the world’s largest datasets on the issue.”

The study also highlights areas of the country with more abnormal frogs than expected. These areas, termed “hotspot clusters”, warrant further research to determine their causes.

Concern about amphibian abnormalities became widespread in 1995 when middle school students discovered frogs with misshapen, extra or missing limbs at a Minnesota wetland. Since then, scientists have continued to report frogs and toads with severe abnormalities and documented global amphibian population declines, disease outbreaks and an increased rate of species extinctions.

In 2000, Congress asked agencies within the Department of the Interior, including the Service and U.S. Geological Survey, to address growing concerns about the health of amphibians in the United States. In response, the Service launched a 10-year study, the largest ever of its kind, to determine the distribution and severity of amphibian abnormalities within the National Wildlife Refuge System. The research effort – called the National Abnormal Amphibian Program – sampled more than 68,000 frogs on 152 refuges, and in the process, compiled one of the world’s largest databases on amphibian abnormalities.

On average, only two percent of the frogs and toads were classified as having skeletal or eye abnormalities, the types of abnormalities most commonly studied. The expected background range of zero to two percent skeletal/eye abnormalities was found at many refuges. Extra limbs were exceedingly rare:  just 0.025 percent of all frogs sampled.

However, consistent with other, prior studies, the Service’s study detected areas where sites with higher rates of abnormalities tend to cluster together geographically. Within these regional hotspot clusters, which were found in the Mississippi River Valley (northeast Missouri, Arkansas and northern Louisiana), in the Central Valley of California, and in south-central and eastern Alaska, abnormality frequency often exceeded the national average of two percent, affecting up to 40 percent of emerging amphibians in some individual samples.

Analysis of the data showed that the location where the amphibians were collected was a better predictor of whether or not they would be abnormal than was their species or the year they were sampled. There was virtually no evidence that some species were more likely to be abnormal than others or that more abnormal frogs were found in some years than in others.  

Although this study was not designed to investigate the reasons behind amphibian abnormalities, the results strongly implicate localized causes. This is consistent with other research, some of which has identified contamination, predators, parasites or the interaction of these as potential factors.

The complete dataset from the study is being made available online at the Dryad Digital Repository (http://doi.org/10.5061/dryad.dc25r ) to facilitate future research to aid in the conservation of amphibians and their habitats. To view the journal article, visit http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0077467.

For more information on this study visit www.fws.gov/contaminants/Issues/Amphibians.cfm.


Invasive Zebra Mussels Found In Cherokee Lake

An invasive species has made its way into Cherokee Lake threatening to disrupt the lake’s ecosystem and clog the lake with harmful and unsightly mussel colonies. Last month, an angler fishing near the TWRA boat ramp at Olen Marshall Bridge in Bean Station discovered what he believed to be zebra mussels.  He contacted the TWRA office and biologists were able to positively ... (click for more)

Photo Contest Underway For 2015-16 Tennessee Wildlife Calendar Issue

The Tennessee Wildlife Resources Agency is now accepting entries for its 2014-15 photo contest for publication in the Tennessee Wildlife Magazine’s annual calendar issue. All interested photographers are invited to submit their best photos on fishing and wildlife species native to Tennessee, and fishing and hunting scenes in Tennessee. Interested photographers must submit ... (click for more)

2 Suspects Sought In Armed Robbery At Highway 153 Long John Silver's

Police are searching for two suspects in an armed robbery that happened Friday morning. At approximately  8:10  a.m. the Chattanooga Police Department responded to 5317 Highway 153 for a robbery at the Long John Silver's.  Officers discovered that two black men, wearing hoodies and masks, entered the Long John Silver's and forced the assistant manager ... (click for more)

Pair Charged With Beating Man With Stick, Taking His Wallet

Two men are charged with beating a man with a large stick while he slept on the steps of a downtown church, then taking his wallet. Jerry Quincy Allen, 45, and James Leo Boas, 40, both of 727 E. 11th St., are charged with aggravated robbery. In the incident on Wednesday, Bradley Casehart said he and a friend were asleep at Tompkin Chapel Church on Palmetto Street. He ... (click for more)

Please Don't Close The Piccadilly Cafeteria At Hamilton Place - And Response

Oh, no. The Piccadilly Cafeteria at Hamilton Place is closing.  Its last day is Christmas Eve.  I will miss the great food they have there but most of all I will miss their servers, cashiers and waitresses.  They are all so friendly and accommodating.  They make it like it’s a home-style restaurant. I sure wish there was some way that Hamilton Place and ... (click for more)

Roy Exum: ‘Scrooge’ Of The Year

As we move into the last weekend before Christmas, the “Scrooge of the Year” has just appeared in Aurora, Ill. Actually Connie Ley has just died. She passed away on Nov. 25, but in her wake left the worst will many around the country have ever heard – her last wishes included that her nine-year-old dog should be put to death, cremated, and buried with her. Bela, a beautiful German ... (click for more)