Dwindling numbers of sharks a cause for concern

Sharks are one among the many apex predators of oceans. Yet, not even that fact can save them from the inevitable consequences of human actions. Since the 1970s, their numbers have dropped by over 70%, and this figure is bound to increase given the pace at which human advancement in the context of environmental disregard is taking place.

Are sharks important components of the marine ecosystem?

Indubitably, sharks are as important as any other organism in the world. Imagine a world where they don’t exist at all. Organisms present at lower trophic levels in a food chain multiply beyond the capacity of the environment. The reason? One of their significant natural predators no longer exists. And the result? Disaster. Lower trophic levels start competing among themselves for food, and greater competition will eventually force them too to disappear. We’ll have successfully killed two birds with one stone.

Whilst sharks help in regulating the abundance of their prey, they also exert a certain amount of control over them with respect to aspects like distribution and behavior. For instance, their presence intimidates animals like turtles. This prevents from overgrazing from a single area of seagrass, thereby also protecting other organisms that live in that habitat.

Ultimately, oceans are empty without sharks.

The case of the Arabian Sea

India is the second-largest shark-fishing nation in the world. However, while sharks are being overfished and pushed towards the brink of extinction throughout the world, the Arabian Sea region has been shining the red signal for a long period of time. Over 50% of the shark species found here are threatened with extinction due to several reasons. While several governmental measures to protect sharks have been enforced (such as prohibition of fishing certain protected shark types or the banning of import or export of shark fin), Indian overfishing has been one of the leading reasons behind the decline of shark populations in the Arabian Sea. Gill nets, long lines, trawls, etc. are dragged through oceans in order to catch large numbers of fish, and sadly, sharks fall prey to this.

Pollution, coastal development, global warming, etc. – all these do impact sharks adversely. However, topping this list of reasons behind shrinking shark populations are fisheries. Be it for making products such as boots and bags, or to consume their meat, overfishing is a serious concern for shark populations as they grow slowly and produce few young,   making them particularly vulnerable to extinction.

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The notion that sharks are monstrous bloodthirsty animals is an encumbrance that needs to be tackled, because the harsh truth is that it is we who are “monsters” that have begun an unfair and endless war against them, as well as the environment as a whole.

“Sharks are beautiful animals, and if you’re lucky enough to see lots of them, that means that you’re in a healthy ocean. You should be afraid if you are in the ocean and don’t see sharks.” – Sylvia Earle

Suffocating marine life to death

While terrestrial organisms like humans enjoy breathing 21% of oxygen present in the air, marine organisms have to depend on a mere 1% of oxygen concentration in water. However, the unquenchable avarice and ridiculous megalomania of humans has started depleting even this small quantity of oxygen.  With the thin line on which the marine world breathes on being vanished rapidly, only adverse repercussions await.

Falling oxygen levels and rising dangers to marine organisms

The diffusion of oxygen from the air into the sea plays a major role in fulfilling the oxygen requirements of marine organisms. Oxygen produced by photosynthesizing marine plants is also used by these organisms to meet their needs.

What happens when the necessary supply of this gaseous elixir is disturbed? Danger steps in. Since the 1950s, oxygen content in oceans has dropped by 2%, and the fact that this figure is only expected to rise in the upcoming years highlights the seriousness of the issue.

Presently, there exist certain pockets of the ocean with little or no oxygen. While such places called “oxygen minimum zones” exist naturally, human activities are expanding these zones and the threats that come with them. But what’s more is that apart from these zones, the levels of oxygen, a gas as essential to marine life as it is to us, are dropping at numerous other places of oceans too.

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What are the reasons behind declining oxygen levels?

Global warming fuelled by human actions is primarily responsible for plummeting oxygen levels. The warmer the oceans become, the lesser the oxygen that can dissolve in them and the greater is the threat to members of the marine world. Ocean de-oxygenation leads to the production of gases such as carbon dioxide and methane which contribute further to global warming.

The discharge of sewage, chemicals and other pollutants into oceans directly also contributes to de-oxygenation. In addition to that, draining pollutants into oceans increases the content of nutrients and favors the growth of organisms such as jellyfish and algae which create an endangering mismatch in the marine environment.

Pockets of low oxygen levels force numerous marine species to search for areas with sufficient oxygen, compelling them to alter their natural behaviors. This may also lead to massive changes in their distributions, posing a threat not only on them, but our economic activities, such as fishing, too.

Human activities that turn blind eye towards the environment are forcing thousands of marine organisms to breathe their last. While we continue pushing for accelerated development, the rich life in our oceans is choking to death. Reforms need to be made, especially on an individual basis, before we lose this environmentally diverse planet from our hands.

Agatti Island of Lakshadweep Atolls: Coral Reef Bleaching

by Rohan Nath


Coral reefs support approximately 0.5 million species worldwide and are considered to be the  most diverse marine habitat. The annual growth of corals is based on environmental  conditions and are severely slow with a growth of only a few mm to 5 cm per year. Natural  and anthropogenic disturbances can influence the changes in the ambient environment and  affect the growth rate of coral reefs. Scleractinian corals get bleached and subsequently die  when there is a loss of endosymbiotic dinoflagellates due to elevated sea surface temperatures  (SSTs). This loss of algal endosymbionts under stress conditions is known as coral bleaching.  Coral bleaching can also be caused due to increased light intensity and salinity increased  copper concentration, as well as exposure to cyanide. There have been 29 widespread  bleaching cases in India since 1989. SST fluctuations have led to large scale bleaching and  mortality of corals in the Lakshadweep Islands, the Andaman and Nicobar, the Gulf of  Kachchh and the Gulf of Munnar. The Agatti Island (Fig. 1) have suffered from local coral  bleaching during 2010 as well as bleaching of coral-associated organisms like giant clams  and sea anemones. 

Fig. 1. An overview of the Agatti Island. Image Source: Google Earth.

Coral Bleaching 

The mortality of coral and associated organisms is prevalent throughout the island (Table 1). Table 1.  

Location Organism Mortality Rate
Northside of Agatti IslandCorals 64%-69%
Sea anemones 81%-83%
Giant clams  70%-85%
Southside of Agatti IslandCorals 75%-85%
Giant clams  83%-91%
Sea anemones  91%-93%

The mortality rate of corals, giant clams and sea anemones is higher on the south side of the  island compared to the north side of the island (Fig. 2). Variation in the depth during low tide  and high tide periods forms a possible reason for the mortality difference between the north  side and south side of the Island. The exposure of the coral reefs of the south side of the  Island to the sunlight during low tide is partial or full while the other sides are not. Low tide  exposure is a more valid reason for the difference in mortality than the elevated sea surface  temperature. The mortality of coral increases in May and June due to bleaching when the  temperature increases resulting in an extended exposure time during low tide and direct  contact with sunlight (Fig. 3).

Fig. 2. Percentage of bleaching in both North and South side of the Island.  Image Source: Vinoth, R., Gopi, M., Kumar, T. T. A., Thangaradjou, T., &  Balasubramanian, T. (2012). Coral reef bleaching at Agatti Island of Lakshadweep  atolls, India. Journal of Ocean University of China, 11(1), 105-110.
Fig. 3. (A, B) – bleached coral; C – bleached giant clam; D – bleached sea anemone. Image Source: Vinoth, R., Gopi, M., Kumar, T. T. A., Thangaradjou, T., &  Balasubramanian, T. (2012). Coral reef bleaching at Agatti Island of Lakshadweep  atolls, India. Journal of Ocean University of China, 11(1), 105-110.

There have been several bleaching events in the past due to elevated sea surface temperature  (Table 2). 

Table 2. 

Location and Year Bleaching  (%)Sea surface temperature of the  corresponding period (°C)Reference
Andaman, 2010 36-39 31-33 Krishnan et al.,  2011
Gulf of Munnar, 2008 10.5 31-33.5 Edward et al.,  2008
Gulf of Munnar, 2007 12.9
Gulf of Munnar, 2006 15.6
Gulf of Munnar, 2005 14.6
Palk Bay, 2002 50-60 32 Kumaraguru et  al., 2003
Gulf of Kachchh, 1998 11
Gulf of Munnar, 1998 82 3 above the seasonal average Arthur, 2000
Lakshadweep, 1998 89

The sea surface temperature of the Lakshadweep reef areas elevated at a rate of 0.21 °C per  decade from 28.50 °C in 1985 to 28.92 °C in 2005. The annual average maximum of sea  surface temperature remained the same, but the annual average minimum sea surface  temperature increased at a rate of 0.30 °C per decade from 27.2 °C to 27.8 °C. The El Nino  increased the sea surface temperature from 1997-1998 to 31 °C. 

Sedimentation and turbidity are also two important factors contributing to corals mortality.  However, the corals of Agatti Island currently do not face such a threat. The bottom  sediments are stabilized by the dense seagrass beds in the lagoon areas. 


There is an average of 73% bleached corals, with bleaching-related mortality of sea  anemones (87%) and giant clams (83%) in the Agatti reefs. The bleached corals need time to  slowly recover in time and replaced by new coral colonies over the old ones. Past researches  proved that corals can recover after the removal of adverse conditions. Coral reefs are  important as a habitat and ecosystem for migratory fishes and need urgent attention. 


1. Vinoth, R., Gopi, M., Kumar, T. T. A., Thangaradjou, T., & Balasubramanian, T.  (2012). Coral reef bleaching at Agatti Island of Lakshadweep atolls, India. Journal of  Ocean University of China, 11(1), 105-110.

The Pondicherry Shark

A shark species that was thought to be wiped from the surface of the earth was not given much attention since the 1970s. But the Pondicherry Shark, a small-sized long-snouted shark belonging to the rare requiem shark family.

We used to be able to find Pondicherry sharks all over the Indo-Pacific region, from the Gulf of Oman to New Guinea. Today, the International Union for Conservation of Nature has classified it as critically endangered today (IUCN).

There are extremely few species of Pondicherry sharks available for study, and we know really little about this species. The Pondicherry shark population was widely distributed in the Indo-Pacific area, but was most commonly found along India’s coast. The bulk of Pondicherry shark specimens come from India, and according to various old stories, the Pondicherry shark occasionally entered freshwater and was observed in the rivers Hooghli and Saigon. If the reports are correct, the Pondicherry sharks’ limited salinity tolerance could be the cause.


The shark species is truly enigmatic, and not much is known about its natural history. The black tips of the dorsal, pectoral, and Tai fins distinguish it. At the base, the front teeth are serrated, and at the tip, they are smooth.

Throughout its range, it is most likely threatened by increasing fishing pressure. Even though the capture of Pondicherry sharks and their fin-export has been banned entirely throughout the country, shark fishing and trade still persists because sharks, with their keen teeth, look similar and are frequently misdiagnosed by fisherman. Shark fins are in high demand in Southeast Asian countries, while shark meat is consumed domestically. Shark pieces are used in the preparation of Sorrah Puttu and other seafood dishes.

Pondicherry penetrates freshwater rivers within its area every year due to its peculiar lifecycle. This indicates that there is a bottleneck near the river mouths, where all the sharks congregate. Unfortunately, this makes them an easy target for unlicensed gillnetters, which has resulted in the extinction of an already elusive shark species.

Sharks play a crucial role in maintaining an intricate balance in nature. As an apex predator, they help to gauge the ocean’s health. Sharks eat larger predatory fish like groupers, therefore their numbers are likely to increase if they aren’t present. A coral reef system’s herbivore fish life is diminished as the population of larger predatory fish such as groupers grows.

This is clearly indicative of what our actions have led to – they have forcibly pushed an entire species of shark to the brink of extinction. Will this rare shark family simply be the next to be forgotten, and erased off the list of scarce creatures that share the same planet as our? There may not be a single answer, but it is certainly not hard to surmise the answer – it is imperative that we change our ways to protect the Pondicherry sharks.

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Olive Ridley Turtles: Conservation of Nesting Sites along the Coast of Odisha

By Rohan Nath


The well-being of a seabeach decides the population of sea turtles residing on them. Sea turtles are highly dependent on land for the reproduction phase of their life. Even though predation of both hatchlings and adults by whales, sharks, large fishes and saltwater crocodiles, play a role in their mortality, the prime reason of turtle mortality is due to certain marine fishing practices. On the beach, predators like birds, beach mammals, insects and crabs’ prey upon both eggs and hatchlings. Hence, threats to beaches which are used as a nesting habitat to the sea turtles hampers the reproduction of sea turtles. Anthropological activities like sand mining, cluttered beaches, developmental activities along the coast and coastal armouring harms the habitat of these sea turtles.

According to WII-DGH Turtle Project Interim Report of 2011, there is a high affinity between sea turtles and their breeding grounds and hence, the whole population can suffer a serious damage due to reduction or loss of even a single rookery. The National Research Council reported in 1990 that urbanization and developmental activities on the coast have destroyed the nesting beaches of the Indian sea turtles.

Several researchers are currently involved in the conservation of the habitat of olive ridley sea turtles (Fig. 1) along the coast of Odisha and how developmental activities affect the sea turtles and their nesting habitats.

Fig. 1. Olive Ridley turtle hatchlings at Gahirmatha nesting ground in Odisha.
Image Source: India Times


The state of Odisha has seven districts with coasts: Puri, Ganjam, Jagatsingpur, Khurda, Bhadrakh, Kendrapara and Balasore with a coastline of about 480km (Table 1) (Fig 2). Along the coast, there are around 250 coastal fishing villages.

Table 1. The coastal districts of Odisha and their characteristics.

Fig. 2. The coastal districts of Odisha.
Image Source: https://www.researchgate.net/figure/Coastal-districts-of-Orissa_fig2_226504527

Developmental activities along the coast of Odisha

The developmental activities along the coast of Odisha are summarised below (Table 2).

Table 2. Developmental activities

The destruction of nesting habitats of sea turtles due to developmental activities

The construction of ports requires the dumping of sand or silt to increase the level of the site of port construction. The biodiversity is affected by the supplementary construction in locations surrounding the port site resulting in an increase in pollution, land use changes, and the destruction of natural habitat. Olive ridley turtles generally breed in the offshore waters of Odisha. The entire food chain of the sea turtles is affected due to the vast amount of dredging of shipping channels which have an effect on the light penetration and turbidity of the water on the benthic habitats. This can result in an increase of biochemical oxygen demand and primary productivity of the water. Intense amount of noise may discourage the adult olive ridley sea turtles from foraging sites and nesting grounds.

Ports, specifically Indian ports in depraved conditions are responsible for water pollutions from cargo discharges, accidental fuel oil leaks and bilge cleaning. Large mega-ports have an adverse effect on the biodiversity of the coast. The breeding sites of the turtles have been degraded by elevated noise levels and pollution. Light pollution hampers the survival of the hatchlings and the nesting behaviour.

The vast number of fish landing centres and fishing harbours and jetties pose a serious threat to the population of the sea turtles. The construction of new fishing harbours and jetties by the Government of Odisha may further aggravate the issue. New fishing harbours might lead to more intense fishing activities and mechanized fishing fleets increasing the accidental catch of turtles.

Casuarina plantations lead to a reduction of nesting space and harms the nesting behaviour of the turtles. It changes the topography of the beach by deposition of litter and its root growth limiting the space available for the turtle to nest. Predators like jackals and hyenas which predates on sea turtle eggs takes cover in these plantations.

Numerous defence facilities and establishments affect the nesting sites of the sea turtles. The training centre INS-Chilika and Golabandha, the missile test programme at Chandipur-on-sea and Wheeler Islands are positioned close to the nesting sites and the target ranges are in the offshore open waters where the turtles aggregate for breeding. Critical behaviours of the sea turtles like, nocturnal sea-finding behaviour and nest site choice of both hatchlings and nesting females are disrupted due to artificial illumination of these establishments.


  1. Behera, S., & Tripathy, B. (2014). Review of current developmental activities and their possible impact on olive ridley sea turtles along the Odisha Coast of India. Testudo, 8(1), 38-55.

Algae – sore reminders of how we pollute water bodies

The night of August 18, 2019 had residents of Chennai enthralled. A night stroll on the Elliot’s Beach turned out to be unforgettable as visitors saw a blue light glimmering the waves that crashed on the shore.

Photo by: B. Velankanni Raj (Image Source)

It was later reported that the Noctiluca algae (commonly known as sea tinkle) were responsible for the magical blue glow on the waves.

While the algae-produced light was fascinating, the reasons behind the sudden emergence of these microscopic organisms is a cause for concern. The sea tinkles in Chennai in 2019 were more than just a treat to the eye. They were reminders of what our activities have wrought.

A rapid increase or accumulation of algae is called an algal bloom. Sewage drainage into water bodies, deforestation, runoff of fertilizers and pesticides, etc. – all these increase the quantity of nutrients present in water bodies. The result? Rapid growth of algae. Rising temperatures of water bodies due to global warming also contributes to surges in the algae populations.

Do algae blooms harm oceans and other water bodies? The sad answer is yes, they do. Massive algae population explosions not only highlight rising pollution and global warming levels, they also impact the environment adversely. By releasing toxins in the water, making water unfit for utilization, and depriving aquatic life from oxygen and sunlight, algal blooms are a dangerous threat to aquatic ecosystems.

Algal blooms have occurred time and again since the early 2000s. In the Northern Arabian Sea, these blooms have been reported annually. The smallest state of India, Goa, and the city of Mumbai too have witnessed such sightings.

Algal bloom blankets a section of the Achenkoil River in Kerala (Image Source)

The negative consequences of human activities on the environment are aplenty – algal blooms are just one of them. Their repeated occurrences point out to the bleak future we are determinedly pursuing.

The Impact of SONAR

Ultrasound – a sound that is not different from other types except humans cannot hear it, and its approximately above 20 kilohertz. But our negligence and malicious methods have led to a devastating impact on the life around us, even though we are unable to feel the pain.

The term SONAR stands for Sound Navigation and Ranging. A few SONAR systems are designed to locate fish, to help catch them easily. SONAR technology though is primarily used for oceanographic research. Through this method, fishing sonar boats send out and receive sound pulses with the help of a transducer, that helps fishermen learn about the distance, depth, etc. Such technology can indubitably benefit them, as it provides for a simple trick to trap large number of fishes in one go. The images formed with the help of SONAR can reveal the precise location of the fish, and at times their numbers too.

A study has revealed that underwater SONAR effects can have shocking impacts on marine mammals, especially whales and dolphins. It was found that exposure to ultrasonic sound disturbed their communication and behavioral processes. In another exercise conducted by the military in the United Kingdom, the number of whales in a particular area drastically fell from over 200 to about 50. The cause? – SONAR.

Even though the impact hasn’t been entirely assessed, evidence provides that whales change their direction rapidly, stop hunting, and swim many miles away when exposed to SONAR.

The consequences of excessive use of this technology is evident. Our wants have put the lives and habitats of thousands of fishes and organisms at risk. We seriously need to review our actions, and its high-time for introspection. The use of SONAR has its benefits, but at what cost are we going to continue risking our future?

The Tragedy of Oil Spills

A dark and murky liquid that despicably spreads over the surface of the sea, and prevents any sunlight or oxygen to pass through, killing thousands of aquatic organisms each year – you have guessed right.

An oil spill is the release or leakage of liquid hydrocarbons such as petroleum onto a water body’s surface. Besides affecting oceans the most, it also has a devastating impact on rivers and bays. Oil spills generally occur due to human errors or accidents involving tankers, ships, refineries, etc. A study revealed that 300 gallons of oil can spread to a radius of 160-feet in a 10 minute span!

Depending on the location of the oil spill, its impact on the aquatic environment varies, though it still persists as an imminent threat to the different species that inhabit the ocean. They can be extremely harmful to fish, sea turtles, and fur-bearing animals such as otters whose insulating ability can be affected. Most organisms tend to digest the oil, which has a shocking effect on growth and reproduction rates.

The spill also hinders the delivery of sunlight and oxygen to aquatic life, thus threatening their survival. Oil can also be pushed to the coastline by waves, tides, and water currents. This permits the oil to interact directly with the sand, gravel, and rocks that are commonly found along the shoreline, resulting in pollution and contamination.

On 28th January, 2017, two ships collided two nautical miles off the Kamarajar port in Ennore, causing an oil spill of 251 tonnes. Local authorities surmised the reason to be human fatigue and failure, which led to the massive collision. A large stretch of the Chennai coastline was affected, and most of the fishing activities had to be called off. But the impact of the oil spill  on aquatic life was horrifyingly dreadful. More than a 100 Olive Ridley turtles washed ashore, dead – during their nesting season. The Ennore backwaters where the spill had taken place drains into the Bay of Bengal, providing a path for the pollutants to reach the ocean. It took more than 5000 people to clear the oil spill.

One mistake is all that takes to damage the environment, ecology, and the lives of humans and animals. Technological advancement and improved construction techniques have still not reduced the number and impact of oil spills. Better measures are needed, both from our side and the government.

Human-produced underwater noise a cause for concern

Nobody likes noise – not us, not animals in forests and not fish in oceans. Loud and cacophonous noise displeases us, and, at times, even leads to dire health issues. But if that’s the case with us, do marine organisms feel the same way about noise? Does noise “displease” fish? Does it cause health issues in organisms that live in the seas?

Ocean Noise Pollution (Image Source)

Let’s look at the world through the lens of fishes. Light does not travel very far in water. So the vision of most fishes is limited to a few metres underwater. Luckily, fishes are very sensitive to sound. Unlike light, sound can travel across massive distances underwater. That’s why most of marine life depends on sound for navigation, reproduction, feeding, communication and even escaping predators.

Marine life depends on sound (Image Source)

And this where we step in. Our activities like commercial shipping, seismic surveys, military sonar and oil and gas exploration cause ocean noise pollution and permeate danger into the already dangerous and fragile lives of marine species. Navigation, reproduction, communication, escaping predators – these abilities of highly acoustic marine animals get damaged beyond repair. Fishes may even be forced to alter their migration routes or spawning sites to keep away from noise.  Besides behavioral problems, marine organisms can face physiologic problems such as bleeding, hearing loss, tissue damage, or even death.

Effects of ocean noise pollution on marine life (Image Source)

Plastic pollution, overfishing, trawling, etc. – these are known to impact oceanic environments adversely. But what remains lesser known is the effects of anthropogenic sounds on members of the marine world. And with noise levels rising precariously, the effects of ocean noise pollution cannot be overlooked.

In January 2016, more than 80 short-finned pilot whales were stranded on the shore in Thoothukudi, Tamil Nadu. In the same year, a 37-foot whale washed ashore in Mumbai. Incidents of stranding like these have been reported at various locations several times. While there is no one specific reason to explain them, it is understood that noise pollution might have a significant hand in their occurrences.

Pilot whales wash ashore in Thoothukudi (Image Source)
Image Source

The fact that noise pollution levels in the Indian Ocean region have come down during the pandemic shines a glimmer of hope during these testing times. But this news should not in any way induce laxity in our measures.

Oceans are naturally noisy environments, with the survival of marine animals being largely dependent on sound. It is we who have intervened in these domains and broken the natural prosody of aquatic life.

While there is increasing awareness of certain perils to oceanic habitats, ocean noise pollution, though not a new phenomenon, needs greater awareness and scientific research.

Foamy Coastline of Chennai

In the last months of 2019, Chennai’s iconic Marina Beach had become the centre of attention in the news.

Locals standing amidst foam-like substance along the coast (Image source)

City-dwellers woke up to an unusual phenomenon on one fine November day. Nearly 1 kilometre of the world’s second longest beach’s shoreline was draped under a blanket of white frothy foam.

This foam formation, as later reported by TNM officials, was caused by the discharge of raw sewage, and industrial and domestic effluents into oceans and rivers.

Witnessing foam on Chennai’s coastline is not something new. Annually, during monsoons, the shoreline is covered with frothing foam caused by various contributors, including waste dumped into water bodies. Waste is discharged into water bodies throughout the year; it is during monsoons that the seriousness of the problem comes into light.

During the rainy season, there is greater inflow of sewage into the city’s sewage plants. This reduces their efficiency, and untreated sewage drains into water bodies.

Frothing is just one of the many negative consequences of waste-discharge into the ocean. As noted by a coordinator at the Coastal Resource Centre, “the foam as such is not dangerous. The real killers are what causes the foam”. Sewage, effluents, chemicals, heavy metals, plastics, etc. – these reduce oxygen levels in water and adversely affect marine life. The poisonous foam produced by these substances also impacts economic activities poses serious threats to human health.  

A child playing in poisonous foam (Image source)

Although foam formation is common event in Chennai, what was witnessed in 2019 was uncommon. The quantities of the fluffy snow-like foam and the area to which it spread posed a major threat to marine and human life. But it was also a shocking reminder of the magnitude by which we pollute our oceans and rivers.