Bangladesh’s Hilsa Fish Acts as Early Warning of Climate Change

Fishermen in Bangladesh are having an exceptional season. The native fish, Hilsa, which normally stays out in the Indian Ocean or the Bay of Bengal in the winter, is swarming along the coastal rivers and estuaries of this small country, and it’s only February.  

pow Trouble is, February is the wrong time of year for such massive schools, which only occur during spawning, or between June and October. The rest of the year, the government typically bans river fishing to allow Hilsa fry, or baby fish, to grow, which they do rather rapidly.  

This annual ban is unfortunate for the Bengali fishermen and their families, who live along the rivers and either sell Hilsa fish for money or eat it themselves. The ban means long winters of subsistence living on the government dole. On the other hand, it’s a very wise environmental practice for food stocks that need to replenish themselves or go extinct.  

Examples of this abound. For example, cod was once an abundant fish along the Grand Banks (Newfoundland, off the Atlantic coast of Canada). Cod fishing literally built the entire Burin Peninsula, in fact, providing a living and a ready source of food for the approximately 30,000 residents.  

By 1996, massive catches had virtually wiped out the cod, and the government was forced to close what had once been the world’s greatest fishery.  

Then it was salmon. Ocean fishing in the Pacific has been restricted for three years, because of low to virtually absent spawning runs. Even now, the salmon are depositing many fewer eggs in the N. California Delta region than were seen as little as a decade ago.  

More recently, the problem is tuna. In each case, an abundance of fish led to dependence on the species for food, and overfishing was the result.  

In the case of Bangladesh, even the fishermen enjoying the current glut of Hilsa (which has caused the government to lift the winter ban) realize that this may be too much of a good thing. However, the prospect of a winter without empty rice bowls and hungry children has largely overcome their concern.  

Hilsa, a national favorite and related to chad, has a mild flavor like walleye, sunfish or trout. Last year, in season, these popular fish sold for about $6 per kilo. This year, in the off-season, but also largely because of the glut, the price is half that.  

Not only are these migratory (anadromous) fish abundant, but their size defies explanation. Normally, Hilsa caught during winter are immature, ranging from 4 to 15 centimeters (or cm; 1.57 to 5.9 inches) in length and weighing half a kilogram at most. Mature Hilsa are generally 32 to 55 cm (about 12.5 to 21.5 inches) long and weigh from 1 to 1.5 kilograms (or 2.2 to 3.3 pounds).  

The overabundance, scientists note, is largely due to changes in temperature in the Indian Ocean which transfer to the Bay of Bengal.  

In fact, according to Dr. Sultan Mahmud, Associate Professor of the Science and Technology Department at Patuakhali University, the surfeit is the result of that warming pattern disrupting mating, migratory and spawning models, and the large fish may be coming into the Bay from the Indian Ocean to breed far out of season.  

Dr. Mahmud and colleagues plan to study the problem intensively, but study will not rectify the fact that Hilsa are being found not only in shallow waters in winter, but outside their traditional fishing zones. And that the pressures disrupting their reproduction will also affect the entire food chain in the Bay.  

The disruption of this ecosphere is perhaps best evinced by a tiny rock island, called New Moore Island, located in the Bay of Bengal that disappeared sometime around 2009, and another nearby island, Lohachara, that disappeared as early as 1996.  

Given warming ocean temperatures, rising oceans that threaten endangered Irrawaddy dolphins and other species, ocean acidity due to CO2 (which destroys coral and the shell-building capacity of mollusks), pollution, and the persistent threat of tropical cyclones and tsunamis exacerbated by climate change, it’s no surprise the native Hilsa fish is in trouble. What may be more surprising is that it has survived this long.  

As Dr. Mahmud notes, the abundance of Hilsa this winter is both astonishing and alarming – a sort of early warning of the kinds of changes in store across species already under stress due to climate change, with no clear indication of where those changes will take us, and thus no clear plan to mitigate disaster.  

According to him:

“It’s not possible to forecast what the situation will be in five years time. The breeding ground of the Hilsa fish has been shifting downstream for decades, due to loss of proper environment. This climate change-induced shift is likely to have important consequences both for spawning patterns and the productivity cycle in fresh water systems, and could be the knock-out punch for many species which are already under stress."

Read other great articles on Celsias:

Finding the Culprit in Extreme Weather

The Imperfect Storm

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Image sourced from: shahidul.wordpress.com

1 comment

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Jon (anonymous)

I this article regarding the fish or just to hype global warming. If its the later where is the data to backup what has been pointed out here.

Written in October 2013

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  • Posted on Feb. 14, 2011. Listed in:

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