Monsoon Diaries Chennai

When a lake takes on a new character

At Kelambakkam lake on November 30. Photo: Prince Frederick  

During the north-east monsoon — especially the kind witnessed in 2015 and probably the one under way now — Kelambakkam lake should go with an alternative carte de visite. It undergoes a temporary change in character, acquiring an enhanced status. During heavy floods, the lake is flush with fish, some not its own. The calling card should be embossed with an image where a trevally shares the frame with a carp.

The lake is always home to brackishwater fish. And in unusual times, it is also “refugee camp” to freshwater fish violently ejected out of their habitats: the freshwater lakes and ponds nearby.

In the evening hours of November 28, despite the skies behaving like a stubborn zipper that would not close up, an informal fish market had sprung up on the narrow landing of a bridge on Kelambakkam-Kovalam Link Road. While hawking the catch from the lake, the sellers seemed its perfect spokespersons, indirectly advertising the lake’s enhanced diversity.

Freshwater fish had flowed into the lake along with the gushing waters that had spilled over from neighbouring freshwater waterbodies: the catch reflected the sudden event. The question to be answered: how long will the catches be eclectic?

Phrasing it differently, how long will the freshwater fish survive out of their familiar waters?

There are freshwater fish that would find this brackishwater lake too salty for their taste. And these would make their preference known in unmistakable terms: they would die — without wasting much time.

A pattern that plays out at the Adyar Estuary
  • In typically estuarine systems where there is a constant interplay between the river and the sea, floods can shake things up for the fish. There is a pattern to which fish survive this turbulence and which are overcome by it — one can witness this pattern in the estuarine system closer home, the Adyar estuary.
  • A Bijukumar, professor and head of the department, Aquatic Biology, Kerala University observes:
  • “Typically freshwater fish that had flowed in from the hill-stream area will not survive when the salinity increases. After the rains, when the salinity increases, some of the fish will not survive. A majority of the fish from downstream and midstream area of the river that have some kind of exposure to saltwater entry, will surive. In the majority of the scenarios in Tamil Nadu, there is entry of salt water into the rivers; and downstream and midstream areas will tolerate brackish water.”

There are freshwater fish that make themselves at home in the brack water due to their capacity for adaptation: they would thrive.

There are other freshwater fish that hold on, barely managing to adjust to their new home, helped by factors, including dilution of brack water: they survive till salinity begins to shoot up.

“If the freshwater fish are directly introduced into brackish water, they will not survive. Here is a scenario where due to the floods, there is a heavy inflow of freshwater, which would cause dilution of brakishwater characteristics. As the process is gradual, the fish can acclimatise themselves to the new environment. There are some freshwater fish that have a higher tolerance threshold to salinity and they would be able to manage in this environment,” notes A Bijukumar, professor and head of the department, Aquatic Biology, Kerala University.

M Yuvan, a naturalist and a member of Madras Naturalists Society’s team that studies and documents biodiversity along the Tamil Nadu coast, notes that at least for a month after the monsoon had generously stirred freshwater into a brackishwater lake such as the one in Kelambakkam, the salinity levels will be abysmally low, enabling many freshwater fish species to continue without much uncertainty to their well-being. Yuvan illustrates: At the peak of the monsoon, even a lake of the size of Pulicat will seemingly take a break from its regular character, registering an incredible drop in salinity levels, due to freshwater influx from Kosasthalaiyar and Araniyar rivers. “Other examples in our parts include the Cheyyur lagoon, which is similarly impacted by the monsoon. Maximum salinity is in the summer, and at other rimes, these lakes are brackish. If you take the Kaliveli lake, only during peak summer does it display a form of salinity. Though a lagoon, by virtue of being tucked deep inside, Kaliveli lake has various kinds of freshwater inflows; and for most part of the year, it is as good as a freshwater lake.”

When the waters go back to being brackish, the freshwater fish that seemed to have survived will find their adaptability being severely tested.

“Catfish is highly adaptable due to the presence of an accessory respiratory organ, and even changes in salinity will not impact them. Tilapia has a long history of surviving in saltwater. Snakeheads also tolerate saline systems very well; and eels do make themselves at home in brackishwaters.”

The freshwater fish that are unlikely to make it past the changed circumstances alive include the smaller barbs. Bijukumar remarks that some of the smaller barbs that are typically freshwater cannot adapt. However, there are larger barbs that are accustomed to backwater systems and put up a performance when overtaken by such events. The loaches are a goner straightaway when thrust into brackishwater systems.

While the freshwater fish were trying to blend in last week, making the most of a changed circumstances, adaptation from another quarters was in striking display. A series of weather systems and resultant choppiness of the sea had put the fishermen at Kovalam out of action, and some turned towards the Kelambakkam lake, with nets, paddle boats and hope.

Even on November 30, when the all-clear had been given to the fishermen on Chennai coast for them to put out to sea, the interest in the Kelambakkam backwaters persisted.

However, as one group reported, the lake was unyielding, doling out only miserly portions of its largesse — the reason being that the lake had guzzled considerable water, which was working out to the advantage of the fish, increasing their longevity.

As the water level had risen, the fish sail over the muddy obstacles in the lake, which normally trap and concentrate them in easily accessed pockets.

Around 7.30 a.m., Gopi Vasanthakumar was winding up, and the catch in front of him was unremarkable — a couple of green crabs; a lone catfish; some tilapia; and small clutches of purely brackishwater fish.

Over to the Kovalam beach, a group of fishermen were lost in deep thought, undecided about venturing out to the sea the same day. They however did not even remotely entertain the thought of carrying their nets to the Kelambakkam backwaters. J Venkatesh and K Venkatesh explained why. For one thing, the freshwater fish do not provide that much of a yield. He illustrated his point by drawing up a comparison between eri veeral and kadal veeral, with the former paling before latter in terms of size.

Two, the best time to fish in the Kelambakkam lake is when it experiences inflows of sea water, which was out of the question at that point as the lake was bloated. Besides, the inflow happens only when the sea is totally at rest, J Venkatesh revealed. On the morning of November 30, the sea still had some lingering irritability carried over from the recent weather systems to deal with.


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Printable version | Jan 26, 2022 2:14:58 AM | https://www.thehindu.com/news/cities/chennai/when-a-lake-takes-on-a-new-character/article37845664.ece

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