Thu, 19 Sep, 2019

The vanishing croak in our backyards

Climate change with prolonged dry-spells diminish frog’s chances of survival & fertilisers that run-off into water bodies can increase dissolved nutrient content and stress frogs

07th June 2019, 02:50 Hrs

Dr Manoj-Sumati R. Borkar  

Rains have arrived and the parched fields will once again magically transform into a visually soothing green carpet of seasonal flora and cultivars. Goa’s countryside in this wet season is mesmerizing; with the palms swaying to the rhythm of south-west torrent, open lush green paddy fields shivering as the rain drops lunge from the dark drooping clouds, paddy farmers and their bulls toiling relentlessly in anticipation of a good harvest, are all surrealistic visuals that one can witness in our land.   

A quintessential note of this monsoon melody is the croaking of the Indian Bull Frog. Anyone who strolls by the fields in Goa at dusk would be greeted by this cacophony emerging from the ponds and pools, the pitch growing louder as the night advances.   

This yellowish-green, big eyed, slithery, ‘long-jump champion of the wetlands’ had once inspired our Konkani poet Manohar Rai Sardesai to pen those famous lines, ‘’ Halduvo taall Bebo, Sheta merer ubo….’’ is reminiscent of the good old days when rains arrived on 1st of June, heralded by the appearance and croak of the Indian Bull Frog in our backyards.   

Regrettably, today our seasons are erratic and the seasonal biodiversity eroded! We are living in times of ‘biodiversity catastrophe’, with rapidly declining species and their fast disappearing habitats. With regular assessments being carried out by International Union for Conservation of Nature (IUCN), there is no doubt that the decline of amphibian species across the globe is alarming.   

The once ubiquitous frog in our Goan fields is no longer offering itself for easy sightings. And one may ask why should we care if we lose the frogs? Well, generations of medical aspirants have sacrificed this animal for their first lesson in anatomy, until the recent ban on use of live animals.   

Frog legs have been on the menu of many restaurants in the state; despite a statutory ban on their trapping, sale and consumption. Their key role in ecosystem function is well recognized, in that their tadpoles browse on algae keeping the water bodies decongested and devour tons of mosquito larvae, keeping a check on transmission of vector borne diseases like Malaria, Filaria, Dengue, Chikungunya, and Japanese Encephalitis.   

Frogs are at a greater peril today than at any time in recent history, as their habitats are being lost faster than ever, due to expanding human population and increasing demand for habitable space. The sprawling megacities have taken a toll of open green spaces and wetlands in Goa. Even the isolated plateaus of Goa which served as amphibian refuges, have been invaded by the concrete carpet!   

Climate change with prolonged dry-spells, further diminish the frog’s chances of survival and seasonal recruitment. Overuse of noxious agrochemicals that end up in wetlands results in toxic build-up in frog habitats, with a permeable skin frogs are vulnerable to bio-sorption as well as bioaccumulation. Fertilizers that run-off into water bodies can increase dissolved nutrient content and stress the frogs, slowing down their growth.   

However, pesticides pose the greatest challenge to their existence. Atrazine, one of most widely used pesticide has been shown to chemically castrate 75% of male frogs exposed to it, whereas the same substance can turn 10% of the exposed males into females! This has serious consequences for maintaining viable natural frog populations in countries where this herbicide is sold without regulatory control. Shockingly in 2018; an enquiry conducted by Directorate General of Trade Remedies under Ministry of Commerce, pertained to subsidized imports of Atrazine from China, clearly suggesting that the substance was in great demand in Indian agro-sector. The substance known to be a carcinogen and cause of congenital defects, can transfer into the frogs and eventually sink in the frog meat consumers.   

Frogs can also be decimated by an infectious fungal disease caused by Batrachochytrium dendrobatidis (Bd). Recently the Critically Endangered Amboli Toad and the Endangered White-lipped Cricket frogs of Western Ghats have tested positive for this fungal pathogen.   

Across the state frog croaks are getting feeble and in some former habitats have vanished completely, suggesting a local wipe out. Wherein there is a general anxiety about declining frog populations in Goa, there is no empirical proof to confirm that, as frog counts have never been tried. Leaf Litter Plots and Nocturnal Transects can give a good idea of diversity and abundance of frogs.   

However in Goa as elsewhere in the country, frogs are not a priority species for funded research. The state dorest department’s research & utilization wing must put in place a team of experts for Rapid Assessment (RA) or Visual Encounter Survey in known amphibian habitats.   

These methods are relatively inexpensive and require shorter time frame.   

Recently, this author and his students have recorded croaks and analysed their spectral characteristics to propose ‘Bioacoustics signature’ for 10 different species of frogs occurring in Goa. This method called the Manual Calling Surveys (MCS) is also useful in auditory monitoring of frog populations.   

Conservation of frogs in Goa shall require an Integrated landscape approach rather than a species-oriented focus. ‘Do No harm’ should be the first consideration followed by statutory protection with punitive provision for prosecution of offenders. The bull frog of Goa is a Schedule IV species as per IWPA, 1972; but a least concern species under IUCN.   

Conserving their habitat, and ensuring good quality of natural water are important considerations, besides restoring degraded habitats and landscape engineering to offer corridors between fragmented habitats can go a long way in ensuring that these precious monsoonal guests can stay back for longer in our backyards.   

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