- Described in 2003, the Indian purple frog is facing heavy threats from habitat loss as its forests are converted to cropland.
- Researchers monitored part of its range for five years, finding that harvesting of tadpoles by local communities may also be taking a big toll on populations.
- But they say community outreach and education programs can help convince people to stop eating them.
The Indian purple frog is an endemic, unique species that occurs exclusively in the southern portion of the Western Ghats. This ancient species has survived for about 120 million years and has witnessed the formation of new continents as well as the extinction of the dinosaurs. But it may be headed towards extinction itself, as its habitat is increasingly destroyed for agriculture. And now, new research published in Salamandra has uncovered a new threat: human consumption.
The Indian purple frog (Nasikabatrachus sahyadrensis) was first described by researchers in 2003. Bulbous, purple, and with a tube-like nose, the species proved distinct enough to warrant its own genus. But the purple frog is highly threatened by habitat destruction as its forests are cleared to grow crops like coffee, cardamom, and ginger. Because of this, it is listed as Endangered by the IUCN.
The Indian purple frog is not alone. Amphibians across the world are experiencing alarming population declines with nearly one-third of about 7,450 species threatened worldwide due to habitat destruction, chemical pollution, climate change, diseases, and invasive species, according to research.
India’s mountainous Western Ghats is a global biodiversity hotspot, including a host of endemic amphibian species found nowhere else in the world. More than 40 percent of the amphibian fauna found within the Western Ghats is threatened with extinction; this includes Critically Endangered species like the Chalazodes bubble-nest frog (Raorchestes chalazodes), the resplendent shrubfrog (Raorchestes resplendens), and Rao’s torrent frog (Micrixalus kottigeharensis).
The major threat to amphibians in the Western Ghats is the alteration of their natural habitat by an ever-increasing human population, which has resulted in large areas being converted for settlement and agricultural use, the study says. “The problem is exacerbated by the fact that approximately one-third of the 203 amphibian species in this hotspot are still categorized as Data Deficient [by the IUCN], lacking sufficient knowledge about their biology, distribution, population structure, population dynamics, and threats faced,” the authors write.
Gururaja KV, Key Scientist at Gubbi Labs in Bengaluru, India, told mongabay.com that 156 new species of amphibians have been described in India in the last 15 years alone – an average rate of more than 10 new species per year. Of the 390 known amphibian species in India, he said, over 200 are data deficient. Without credible data to indicate population trends and threats, there is no way of knowing how threatened these species are.
But the discovery of the Indian purple frog, Gururaja reckons, was a game-changer for India’s amphibians. Hailed as a once-in-a-century find, the purple frog has garnered considerable scientific and public attention since the discovery due to its secretive behavior and unusual appearance, focusing international attention on the diversity and conservation of the Western Ghats.
Now, researchers have added another threat to the purple frog’s survival. Ashish Thomas, author and principal investigator of the latest study published in Salamandra, is an assistant professor of environmental studies at the University of Delhi. As part of his PhD research, Thomas found that an old practice of consuming the endangered purple frog’s tadpoles by tribal communities in India’s southern state of Kerala, might push the species towards extinction.
The researchers conducted a five-year survey from 2008 to 2013 in Kerala’s Idukki region, where tadpole consumption is prevalent.
“The practice of consumption is an old one based on information from elders aged between 80 – 100 years,” Thomas told mongabay.com. Although the elders mentioned that they had consumed these tadpoles when they were children, the consumption at this particular study site has occurred for only about 40 years or so, since this communities first settled in the area.
Thomas and co-author SD Biju, who was part of the team that described the species in 2003, believe continuation of this practice could lead to local extinction.
Adults of the species remain underground in burrows for most of the year except for about a two-week period in pre-monsoon season when they come out to breed and lay eggs. Because tadpoles are available for only a small period of time every year before they metamorphose into adults, the communities that eat them consider them a delicacy.
There are about 100 to 150 tribal households in the study area, which is adjacent to the Idukki Wildlife Sanctuary. On an average, the researchers found a household of four people consumes approximately 1,500 tadpoles – or three kilograms – per season.
The harvest season is critical because it coincides with the period when tadpoles are at the advanced stages of development.
“Because [the] number of individuals recruited back into the population is drastically reduced due to the timing of the harvest season,” Thomas said. Another concern, he says, is that populations of most amphibian species have a “highly skewed” sex ratio – for every 10 males, there is only one female. As fewer individuals are recruited back into the population, the harvesting of tadpoles will additionally affect this sex ratio. This may affect the number of breeding frogs in the future, he said.
Researchers found that even though the consumption of these tadpoles was common practice in other tribal areas as well, they did not observe the residents in the study area selling the collected tadpoles for a profit. Additionally, they found that some tribal people also eat adult purple frogs. Since adults emerge from burrows only for two weeks during the year, the researches worry this could reduce the breeding population.
The researchers say that the purple frog population in the area had already significantly declined based on interviews with locals.
“Tribals and locals do testify that populations were much higher 10-15 years back as compared to the scenario now,” Thomas said.
The number of tadpoles harvested by community members follows a similar trend, the study says, declining during the five-year study period. Exacerbating the problem, pre-monsoon rainfall was very erratic in 2011 and 2012 in comparison to previous years. This resulted in streams drying up quickly and staying dry for long periods during the frog’s breeding season. The researchers also saw a few egg clutches within the study site that had dried up. The marked decline of tadpoles in the study during these two years could possibly be a cumulative effect of both scant precipitation and harvesting, the authors write.
“Such a possibility indicates that even if harvesting is carried out at sustainable levels in the region, other direct and indirect threats (most of which are either subjective or undocumented until now) could significantly augment the threat of harvesting in the near future and lead to a substantial decline of local population of the purple frog,” the study says.
However, the researchers admit that it’s possible their findings were skewed by the relatively short duration of the study.
“Amphibian populations are known to fluctuate considerably in size from year to year due to stochastic factors [like the frequency and amount of rain, the presence or absence of predators, the impact of pesticides, etc.], especially in the case of seasonal and/or explosive breeders,” they write. It is thus imperative to conduct long-term monitoring studies to identify the influence of this direct threat on local purple frog populations, they advise.
The authors write that there may be hope for the Indian purple frog. With some sensitization and tribal education, they believe that they can convince communities to stop harvesting these endangered tadpoles.
“Most tribals engaged in harvesting are young, in the age group of 20 – 40, since it requires skill to maneuver on the extremely slippery rocks of these torrential streams,” Thomas said. He said that there have also been deaths from people having slipped on these rocks so for those who do engage in the activity, it is a kind of adventure. “Just like one goes fishing as a hobby or past time (sic.), the same is the case for the tribals. It’s kind of [a] ‘cultural hobby.’ We believe if these people are engaged in some job, they will reduce such risky undertakings.”
Thomas says researchers are hopeful that education programs tailored specifically for the benefit of the tribal communities will go a long way towards the purple frog’s survival in the region.
“As our sensitization and awareness efforts have yielded positive results, we surely feel that tribal-friendly programs will be quite impactful in this case,” he said.
The authors suggest that conducting awareness campaigns among tribal and local people could be an important conservation management step for this species. As most tribal people involved in tadpole-harvesting are unemployed youth, an underlying factor could be that they are not engaged elsewhere and look for an easy way to make a living.
“Society and conservation managers could design specific measures to educate tribal people and provide them with basic amenities and employment opportunities,” they write.
In fact, after the consequences of harvesting these endangered tadpoles were explained to them, five families stopped harvesting purple frog tadpoles during the five-year survey, according to Thomas.
“The point is that maybe in the distant past when the purple frog was neither rare nor endangered, this practice may not have made a significant dent in the overall population of this species,” Biju said in a statement. “Times have changed drastically and the purple frog now perilously survives only in a few pockets.
If the purple frog tadpoles continue to be on the tribal menu as a monsoon delicacy, the local population[s] of these frogs are destined to disappear.”
- Thomas, A., & Biju, S. D. (2015). Tadpole consumption is a direct threat to the endangered purple frog, Nasikabatrachus sahyadrensis.