Pingers and an Attempt to Save the Ganges River Dolphin

I make my way through the thickets of reeds that line the waterfront of the Hooghly River in West Bengal’s Purbha Bardhaman district. The silt-laden banks crumble underfoot as I tread carefully, oscillating my field of view between my next footing and the water that flows so effortlessly to my right. A fisherman in his dunga (diminutive tin craft) passes by, unfurling his net as they float downriver in perfect synchrony. I signal to him and use my hands to gesticulate a dolphin breaching. He smiles back and points ahead, a little beyond where the river turns left.

I continue for a little bit, till I hear a sound I have not heard before, but it is so distinct that it leaves no doubt in my mind. The swooshing of a Ganges river dolphin (Platanista gangetica gangetica) spouting. I wade into the murky brown water, distracted briefly by the soft sediment that melts away and envelopes my feet in surprising warmth. Then, almost as if out of a dream, the dolphin breaches again, less than ten metres from me. I hold my breath. Is it going to breach again? Is it curious about me? Should I wiggle my toes underwater to draw its attention? But that was it. The fairy of the Hooghly disappears as quickly as it came, leaving no sign that it was ever around. I sit down at the banks, scanning the water once again till I see it 20 minutes later, a distant speck, breaking ever so slightly through the surface, on the trail of the fisherman who had passed me. 

Interactions between dolphins and traditional freshwater fishers in West Bengal are on the rise. Ganges river dolphins have evolved to life in the highly turbid waters of the Ganga and Brahmaputra River systems and are functionally blind. They rely almost entirely on echolocation to navigate and hunt. The dolphins are unable to “see” the thin monofilament gillnets that are used by traditional fishers, only detecting the frantic vibrations made by stressed fish as they try to break free. This promise of any easy meal drives dolphins close to active gear, resulting in one of two outcomes: them successfully making away with the fish, as they do in most cases, or getting entangled in the nets themselves. While seemingly benign, this interaction has immense socio-ecological consequences, threatening dolphins with accidental entanglement in fishing gear and burdening fishers with catch loss and damage to their nets.

“At one time, this was a river of abundance” says Shanto Rajbanshi, a current jaal fisher from Naliapur village. “Now it is almost as if we are competing with the dolphins for whatever fish are left.” Shanto has fished the Hooghly for over three decades, and like most fishers believes that this increase in the frequency of interactions with dolphins can be attributed to dwindling fish stocks and restrictions to the species linear habitat, imposed by the erection of a barrage along the river.

Shanto is now one of the fishers participating in trials by WWF-India and partners, to understand the effectiveness of an acoustic deterrent (pingers) at reducing Ganges river dolphin bycatch in this traditional gillnet fishery.

The application of acoustic deterrents, or pingers, in commercial marine fisheries has demonstrated significant potential at a global scale for effectively reducing or even eliminating marine mammal bycatch. Pingers emit clicks that are audible to dolphins — the acoustic equivalent of a neon billboard — which deters the animals from the active fishing gear when the devices are attached. Given that accidental entanglement in gillnets is one of the leading threats faced by all four extant species of river dolphins, it comes as no surprise that pingers have been getting significant attention from the conservation community as a potential solution to the river dolphin bycatch issue.

Some of the most successfully concluded pinger trials in freshwater systems include those by the Yayasan Konservasi RASI (Rare Aquatic Species of Indonesia), in Indonesian Borneo, to protect the last 80 remaining Irrawaddy dolphins in the Mahakam River. The findings from this study showed that the dolphins did give a wide berth to pinger equipped nets — resulting in no instances of entanglement as well as a 40 per cent increase in fishers’ total catch over the course of the study. Since 2023, WWF-India along with the West Bengal Forest Directorate, the Wildlife Institute of India and local fishing communities, have been conducting trials to understand the efficacy of pingers at reducing Ganges river dolphin bycatch in West Bengal. Following the first trials undertaken by the Wildlife Institute in the Brahmaputra River in 2022, these trials mark only the second time that a long-term experiment such as this has been undertaken in the country.

Over the course of the experiment, which ran for a total of 70 days, nets were deployed both with and without pingers in ten-day phases. During this period, instances of dolphin breaching, along with proximity of the animals to the pingered and non-pingered nets were recorded by the field team. These visual observations on dolphin presence and activity were supplemented using specialised hydrophones, known as F-pods, that were placed 500 meters up and downstream of the setup. Given that Ganges river dolphins vocalise, almost continuously, any dolphins entering or exiting the study area are picked up by these hydrophones. This is especially useful, since the dolphins can go up to two minutes without surfacing and sometimes leave as little evidence as ripples on the water’s surface when they do.

“While the project is still in the early stages, the results so far seem promising” says Shahnawaz Khan, Lead Ganges Dolphin Biologist at WWF-India. “Based on the data so far and feedback from fishers participating in the trials, dolphins do seem to avoid nets which are equipped with pingers without any visible changes to their foraging and social behaviours. We will have to wait to have a large enough sample size to say this conclusively.”

Dr Pradip Bauri, DFO, Nadia Murshidabad, West Bengal Forest Directorate said, “We are excited about these initial findings and look forward to scaling up the pinger trials. If found to be effective over the course of long-term studies, the next steps will involve working towards subsidizing pingers so that it is economically feasible for fishers to use them during operations.”

Findings from the study indicated that the quantity and composition of fish catch was not negatively impacted by the use of pingers. However, despite this early success, concerns do exist regarding the use of pingers as bycatch reduction devices and how they impact dolphins. These include the risk of gradual acclimatation of dolphins, with some studies even pointing out that it could possibly build an association between pingers and food — referred to as the “dinner-bell” effect. Other concerns include behavioural changes and habitat avoidance by dolphins from this additional source of underwater noise. A few commercially targeted marine fish species are also known to avoid pingered nets, resulting in a decrease in the quantity and quality of catch for fishers when using pingers on their gear.

Given the dearth of long-term work surrounding the use pingers in freshwater habitats, site-specific studies such as this are needed to understand at a fine scale their effectiveness at reducing river dolphin entanglement. These localised studies allow for conservationists to assess how dolphin behaviour changes in the presence of pingers, while also demonstrating the impacts, if any, on a fisher’s total catch. Conducting trials across our rivers is an essential first step before pingers can be presented as a singular solution — using these devices to eliminate river dolphin bycatch and secure the livelihoods of traditional fishers.

 

This work is funded by a Darwin initiative grant and is part of a joint project along with the West Bengal Forest Directorate, the Wildlife Institute of India, WWF International, Chelonia Ltd., Fishtek Marine and community members from Naliapur village.