Environment

Keep the exotics out of our waters

A brimming lake but how healthy is it?  

Coimbatore has been seeing a lot of rain in the past few months and, thanks to that, our lakes are brimming with water. As long as the water bodies are full, everyone thinks all is well. “Not really,” says Dr Sanjay Molur, Executive Director of Zoo Outreach Organisation, who has also been working to enhance the biodiversity aspect of the lake restoration project in the city. “The lakes may well be dead from an ecological perspective.”

An ideal stream inlet with a variety of vegetation

An ideal stream inlet with a variety of vegetation  

One of the most important aspects of keeping a water body alive is the quality of the input. “Today our inlets are mostly sewage lines. Like Achankulam,” says Sanjay. Haphazard urbanisation leading to encroachment on the inlets is another issue. “Most lakes were gravity-fed water collection spots but not any longer.” Sewage treatment plants are important but there is another aspect as well. “We keep saying these lakes were bigger and held more water in the past. Why? Because the area was larger.” Now what we do is to increase the depth by desilting. “It’s the worst thing to do,” Sanjay exclaims. “Desilting removes an entire wealth of biodiversity and rich soil. Since the bed is still moist, life forms continue to exist in cracks and crevices and come to life when it next rains.” This goes for the inlets as well. Dredging inlets in dry weather will remove the dormant parts of the native vegetation, which are crucial in maintaining the lake's ecological profile. “When you desilt a lake, its profile becomes a deep bowl with no biodiversity allowing people to fill it with exotic species,” he rues.

Which brings us to native flora and fauna. He shows photos of a lake in Bengaluru: full of water, green islands, trek paths... It looks beautiful but points out that the water is overly green. And that, he says, is due to a lack of biodiversity. “We need to differentiate between eco-restoration and beautification. The ideas are perhaps influenced by lake fronts abroad with promenades and walkways and places to sit. Which is fine. But the vegetation and aquatic life must be local.” Not exotics like the water hyacinth, which deprives the water of oxygen spelling doom for other life forms.

Albizia lebbeck or the Indian Raintree

Albizia lebbeck or the Indian Raintree  

Sanjay points out of his office window to a large tree. “That is the Indian Raintree (Albizia lebbeck). Unfortunately it has been replaced by the exotic Avenue Raintree. The native species has golden yellow pods after the flowering. When the wind blows, the shaking pods create a sound like a waterfall.” Eco-restoration around lakes is an opportunity to bring in native species and “we should look not just at big trees but also medium and small ones, apart from a variety of shrubs and plants.” The good news, he says, is that these are all available.

The exotic African catfish has taken over most of our waterbodies

The exotic African catfish has taken over most of our waterbodies  

Next, Sanjay shows a video of a lake with what looks like a fish fight in one corner. “Those are African catfish. Notice that there’s nothing else on the lake. Not even a single bird.” At my surprised look, he nods, “The birds can’t eat these; it’s more likely that the fish will attack them.” Sanjay explains how many lakes are auctioned to fisherfolk who release spawns of exotic fish like tilapia (from Mozambique), rohu, katla... “The last two are native to the Indo-Gangetic belt; not to Coimbatore region. Just because it is Indian doesn’t make it native to this region,” he emphasises. He calls this the positive feedback loop of negativity to an ecosystem, when people think they’re doing something good and actually make matters worse.

The Channa Gachua was a delicacy just over 20 years ago

The Channa Gachua was a delicacy just over 20 years ago  

What are the fish species native to this part, I ask. He reels off the names: Hypselobarbus, snakeheads like the Channa Striata, native catfish like the Dussumieri, Anabus or climbing perch … “all these are food fish. They were considered delicacies and part of our diet 20 years ago. It has taken just one generation to move from native to exotic fish. I don’t see why the reverse can’t happen.” To help with that, Zoo Outreach Organisation is partnering with other organisations to develop breeding technologies for native species. “We have an initial set of spawn; it’s a slow process but, in a couple of years, we should have enough native species to transplant into our water bodies.”

Sanjay agrees that convincing stakeholders is important for this strategy to succeed. “We need to work with local communities and fisherfolk to ensure that their livelihoods are not affected by making this change.” One of the ways, he feels, is to retain Environmental and Social Impact Assessments wherever the project involves biodiversity. “That’s because a lot happens in the name of ecological restoration that shouldn’t.”

Local to the region

Native trees: Pongamia pinnata (Pongam); Mimusopselengi (Elengimaram); Ficus benghalensis (Banyan Tree); Ficus religiosa (Peepal Tree); Terminalia arjuna (Marudhamaram); Syzygium cumini (Jamum Tree)

Native species of fish: Ananbas testudineus (climbing perch), Etroplus suratensis (karimeen) and Pseudetroplus maculatus (pallathi) are omnivorous, cleaners and scavengers; Cirrinus cirrhosus (white carp); Systomus sarana (olive barb); Barbodes carnaticus (Carnatic carp); snakeheads Channa marulius, Channa striata, and Sperata seenghala and native shrimp like Macrobrachium malcolmsoni

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Printable version | Mar 6, 2021 5:39:41 AM | https://www.thehindu.com/sci-tech/energy-and-environment/why-we-should-bring-back-native-flora-and-fauna-into-our-wetlands/article25668937.ece

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