How pollution affects fisheries

Scientists have been studying the vulnerability of nations across the globe to the impacts of climate changes on fisheries. They have found that ...

How pollution affects fisheries

“Warm tropical waters, azure blue seas enveloped by pristine beaches...” reads a pamphlet beckoning tourists to the Karnataka coast. The mental image of those beautiful shores catches the attention not only of tourists who flock there in the thousands, but also of an aquatic traveller who has visited these waters for generations; the ladyfish or kane. Sticking close to the shores all across the Indian and Pacific Oceans, this fish has wormed its way into local culture and cuisine.

Coastal Mangalurean food cannot be complete without kane rava fry. Foodies interested in the history of this dish should start their journey not with grandmothers’ tales, but with a visit to estuaries, sand-bars and mangrove creeks, where the ladyfish is found. Once there, the interested foodie can peel back the layers of deep fried rava, in order to meet the kane, a fish with an active social life, which likes to travel and lives the good life in well-lit, warm, shallow waters.

The ladyfish enjoys seafood too. It feasts on prawns, marine worms, shrimp and other crustaceans to pack on the flesh that makes for rich pickings through its bony skeleton. This adaptable fish can travel between coastal waters, estuaries and even rivers, without needing any obvious physical modifications to help it to survive the change in salinity. When threatened by predatory dolphins and sharks, it can also depend on its group (called a school) for any assistance.

The ladyfish meets romance in estuaries. This is where they breed, lay eggs and this is where the little larvae feed and grow into the half metre long fish that are preferentially served in restaurants. However, the ladyfish also meet a lot of other things in estuaries, including industrial effluents, sewage and pollution. These fish react to danger by burrowing into the sand to escape from some fishing nets.

Effluents and chemical pollutants, however, leave no room for escape. The ladyfish’s life is becoming increasingly stressful due to pollutants in the water that it breathes, constantly needing to be one step ahead of the bottom dredging nets, while trying to give its young ones the best possible start to life.

Unfortunately, the ladyfish’s polluted environment is exactly where the urban tourists are headed to make their escape. Both the fish and the tourists dream about the pristine images on the Karnataka tourism pamphlet. But the reality is that, what they meet with is far from pristine.

River mouths and estuaries face the most intense fishing pressure and are also subject to large-scale alterations in terms of dredging, port building etc. This disturbance to the marine ecosystem has serious repercussions for fish populations. During recent research with fishermen on the west coast of India, I discovered that the ladyfish along with other estuarine species are some of the first to disappear due to human activities.

Overfishing in coastal areas is certainly a cause for dwindling schools of ladyfish, but fishermen suggest that with a burgeoning number of dams squeezing the life out of rivers, there is little nutrient-rich freshwater left to support life in estuarine fish nurseries. This theory has been borne out in a number of cases across the world.
Dams decrease freshwater input into estuaries, drastically increasing their salinity, concentrating pollutants and other chemicals by excessive evaporation. Rather than simply blaming overfishing for a decrease in ladyfish populations, a complex set of threats need to be addressed to save the kane for our plates.

The natural history of the kane rava fry, in this age of chemical pollutants, can be far from appetising. But urban tourists have a goal in common with the fish that will complete their coastal holiday dinner, a healthy, pollution-free coastal zone. In fact there is just a small window in which this environmental quality needs to be assured – November to March – the peak breeding season of the ladyfish according to the Central Marine Fisheries Research Institute. Ensuring that fishermen can catch large ladyfish for their plates requires that estuaries are well preserved and can support a healthy population of ladyfish larvae.

A study by scientists from five different countries, on the vulnerability of nations across the globe to the impacts of climate change on fisheries found that India, due to its high population of fishermen and high harvest rates, would face severe strain on its sea fish resources due to climate change.

The Indian fishery’s capacity to adapt to climate change was also assessed as low. It is not clear what the exact impacts of climate change will be, but what is clear is that there is a need to plan for change, and ways to slow down its impacts. Huge fuel consumption rates are also accompanied by oil slicks, as unburned fuel and the kerosene used to start the engines leak onto the surface of the sea. Of course the impact of this spillage is minimal compared to oil spill disasters, and to the carbon dioxide and monoxide being
released.

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