Why do thousands of shells wash up on the shores of Karachi every monsoon?

Every year, around June, Karachi’s beaches become crowded – not only with people, but also with shells, hundreds of thousands of them, spread across the shore in dense, noisy shoals. This sight left the citizens intrigued, with many wondering if something was wrong. The same thing also happened in June.

In recent days, there have been discussions online and offline about why this phenomenon is happening. Was it climate change or the spectacle of nature?

Science and fishermen tell a story on many levels.

A prelude to the monsoon

The phenomenon is not new. A Dawn report dated July 17, 2009, noted that large numbers of white and yellow shells had appeared on Clifton Beach overnight. Another Dawn reportdated May 21, 2016, reported that wave action dislodges shellfish, particularly Venus clams, locally known as “burgar”, from shallow subtidal habitats, carrying them to beaches where they die and leave behind empty shells.

The same event was also covered by The Express PK Press Club on May 22, 2016. Both reports claim that the phenomenon is linked to the arrival of the monsoon.

A Aaj News report dated July 10, 2024, also notes that marine experts continue to identify June and July as the recurring seasonal window for this phenomenon, while adding that increased pollution levels could contribute to higher marine mortality rates, leading to greater volumes of shellfish washed ashore in some years.

Majeed Motani, president of Pakistan Fisherfolk Forum, who has decades of experience in fishing, confirmed this. The phenomenon is not new and is known locally as ‘aokar’, he said, and similar shells can be seen along several coastal areas, including Ibrahim Hyderi and other beaches in Karachi.

“We have been witnessing this phenomenon for decades, especially in June and July,” he said, explaining that water from the deeper parts of the sea rises to the surface and eventually pushes the shells towards the shore, where they are deposited along the coastline.

What the science says

Scientific research on the Arabian Sea provides a clearer explanation of why this happens. When the southwest monsoon arrives around June, strong winds push warm surface waters away from the shore, carrying cold water from the depths of the ocean – a process known as upwelling.

A study published in the Journal of Sea Research explains that these cold, deep waters contain very little oxygen and when they spread across the sea floor, they prove deadly to bottom-dwelling creatures, such as clams and other shellfish, which cannot move quickly enough to escape. Their empty shells are then transported to the beaches by the powerful monsoon waves.

PHOTO: DAWN

A separate paper on the Arabian Sea shelf, published in Deep-Sea Research, found that cold, oxygen-deficient water begins to appear off the coast of Karachi as early as June and persists until November, precisely the months when citizens observe the highest concentrations of shellfish along the coast.

Another study said the monsoon season coincides with the period when the highest number of marine invertebrates are present in the coastal waters near Karachi. In short, shellfish populations peak near the coast when the harshest ocean conditions arrive, which is why beaches receive so many shellfish.

The anomaly

But 2026 could be a different year in at least one way. Motani told iVerify Pakistan that the number of shells this year seems higher than usual.

Fatima Yamin, an expert on climate change and disaster management, pointed out that India’s National Center for Ocean Information Services issued a marine heatwave advisory in April confirming that parts of the Arabian Sea – including the coasts of India, Pakistan and Bangladesh extending towards Oman – are on high alert due to an increase in sea surface temperature anomalies.

“Whether this will affect deep waters remains to be seen, but it would impact the continental shelf. This correlates with accounts from fishermen who have never seen such large numbers of marine shells washed up on shore before. Warmer sea surface temperatures can also change oxygen levels, causing marine life in the water to die off and possibly causing marine mammals to come to the surface in search of oxygen,” she added.

What happens to the shells?

Meanwhile, the shells themselves are not wasted.

According to Motani, some people – mostly families living near the sea – collect them to make a living. The shells are cleaned using chemicals and other methods and then used to make jewelry, photo frames, decorative items, flower pots, and other handicrafts sold in the market.

Beyond crafts, shells also have a broader industrial value, increasingly explored by researchers. A study examining sustainable waste management found that shellfish can be converted into biocalcium carbonate through a high-temperature calcination process. When used as a filler in high-density polyethylene (HDPE), a common industrial plastic, the shell-derived material has been shown to improve the thermal stability, crystallinity, and tensile strength of the plastic, while only slightly reducing its flexibility.

This article was published by iVerify Pakistan as part of its initiative to combat climate myths and misinformation, supported by Irada and IMS.