Narwhals: Understanding The Impact Of Pollution On Their Habitat

The majestic narwhal, with its distinctive spiralled tusk, is under threat from human-caused pollution and climate change. These factors are reshaping the Arctic, the narwhal's natural habitat, and causing increased exposure to toxic pollutants like mercury. Human activities such as fossil fuel combustion, shipping, and industrial extraction contribute to both climate change and noise pollution, which negatively impact the narwhal's ability to navigate, communicate, and find food. With their sensitivity to underwater noise and limited ability to eliminate environmental contaminants, narwhals are particularly vulnerable to the effects of human-induced pollution and climate change.

Narwhal tusks reveal mercury exposure

The majestic narwhal, known for its unicorn-like tusk, is facing a significant threat due to human activities. The tusk, which can reach up to three metres in length, is not just an intriguing feature but also a valuable source of information about the health of these mysterious creatures and the Arctic ecosystem.

An international team of researchers, including Jean-Pierre Desforges, a Postdoctoral Fellow at McGill University, and Professor Rune Dietz from Aarhus University in Denmark, has utilised the natural growth layers in male narwhals' tusks to study the impact of pollution. Each year, a new layer is added to the tusk, akin to the rings in a tree trunk. As the tusk is connected to the narwhal's body through blood, each layer records physiological information, such as diet and exposure to contaminants.

The analysis of these tusks has revealed a disturbing trend of increasing mercury exposure in narwhals since the 1960s. This rise in mercury levels is attributed to human-caused carbon emissions and sea-ice decline linked to climate change. As Desforges explains, heavy metals like mercury accumulate in the body through the food chain, and the higher the species is in the food chain, the more mercury it accumulates. This accumulation can have toxic effects on cognitive functions, behaviour, and reproductive abilities.

The research found that until around 1990, narwhals primarily fed on prey linked to sea ice, such as halibut and Arctic cod. However, as ice cover declined, their diet shifted to open ocean prey like capelin and polar cod. Despite this change in prey, which placed them lower in the food chain, the amount of mercury in their tusks significantly increased from 2000 onwards. This indicates that the rise in mercury is primarily due to human emissions, particularly the ongoing combustion of fossil fuels in South-East Asia.

The findings highlight the vulnerability of narwhals to climate change and pollution, as they lack the physiological mechanisms to eliminate environmental contaminants. With each layer of the tusk offering a window into the past, researchers can now analyse museum specimens to better understand narwhals' feeding strategies and evaluate their ability to adapt to the changing Arctic conditions.

Human emissions and climate change

The Arctic region, home to narwhals, is warming twice as fast as the rest of the planet. This rapid warming is largely attributed to human-induced climate change, with human emissions playing a key role. The burning of fossil fuels has led to a sharp rise in the presence of toxic pollutants like mercury in the Arctic. This increase in mercury emissions has been linked to ongoing fossil fuel combustion in South-East Asia. As a result, narwhals have experienced higher levels of mercury exposure, which has accumulated in their bodies over time. This accumulation of mercury can have detrimental effects on their cognitive functions, behaviour, and reproductive abilities.

In addition to the direct impact of human emissions, narwhals are also affected by the indirect consequences of climate change. The reduction in sea ice cover in the Arctic has disrupted their habitat and food sources. Sea ice plays a crucial role in the narwhals' annual cycle, providing them with protection from predators such as killer whales. However, due to warming temperatures, the sea ice has been declining consistently since 1990, affecting the entire Arctic food chain and the living conditions of all species, including narwhals.

The loss of sea ice has also led to changes in the narwhals' diet. Before 1990, narwhals primarily fed on prey linked to sea ice, such as halibut and Arctic cod. However, as the ice cover declined, they shifted to open-ocean prey like capelin and polar cod. This dietary change may impact their energy intake, as Arctic species tend to be more nutritious and energy-dense due to the need to survive in colder temperatures.

Moreover, the reduction in sea ice can increase the risk of ice entrapment for narwhals. Sudden changes in weather conditions, such as shifts in wind or rapid drops in temperature, can freeze the leads and cracks in the ice that narwhals use for breathing and migration. This entrapment can result in the deaths of hundreds of whales.

Overall, human emissions and climate change have had far-reaching consequences for narwhals, affecting their exposure to toxic pollutants, disrupting their habitat and food sources, and increasing the risk of entrapment. Addressing these issues and mitigating the impacts of climate change are crucial for the conservation and survival of this vulnerable species.

Narwhals' sensitivity to underwater noise

Narwhals are one of the marine mammals most sensitive to underwater noise. Two studies found that narwhals show signs of stress in response to underwater noise. These findings are important for both narwhal conservation and for Arctic marine planning.

Whales use sound to navigate Arctic waters. While the breaking of sea ice, calving of glaciers, and breakdown of icebergs all cause familiar sounds, it is the unfamiliar human activities that cause noise pollution and disturb whales. These activities include shipping, seismic exploration, pile-driving, ice-breaking, and sonar activities.

Like other whales, narwhals use sound to see, hear, communicate, navigate, and assess their surroundings. They are greatly impacted when unfamiliar noise enters their habitat. The studies found that narwhals displayed avoidance reactions when exposed to underwater noise, swimming away from the sound and towards the shore. They also increased their swimming speed when exposed to ship traffic.

The studies also found that underwater noise affected the feeding behaviour of narwhals. They first decreased and then eliminated their buzzing rate (fast-clicking sounds made when searching for food) when ships or seismic airguns could be detected. At 12 km from a noisy ship, narwhals buzzed half as much and stopped buzzing altogether when the ship was 6-7 km away.

These findings place narwhals at the top of the list, along with beaked whales and harbour porpoises, as the most sensitive species of whales and dolphins to human-made noise. Continual disruption of narwhals during feeding could easily affect their body fat reserves, reproduction, and even survival.

Impact on feeding behaviour

The impact of pollution on the feeding behaviour of narwhals is significant. As top predators, narwhals are highly susceptible to the presence of toxic pollutants in their environment, such as mercury, which has been increasingly found in their systems due to sea-ice decline and human-induced carbon emissions.

Narwhals' feeding behaviour is influenced by the availability and distribution of their prey, which is, in turn, affected by the decline in sea ice. Before 1990, narwhals primarily fed on prey associated with sea ice, such as halibut and Arctic cod. However, as sea ice coverage decreased, their diet shifted to open ocean prey, including capelin and polar cod. This change in diet should have resulted in lower mercury levels in narwhals, as these new prey sources sit lower in the food chain.

However, research has revealed a surprising increase in mercury levels in narwhals' tusks after the year 2000, indicating a significant shift in their exposure to pollutants. This rise in mercury emissions has been attributed to ongoing fossil fuel combustion, particularly in South-East Asia. Additionally, changes in sea ice conditions due to warming climates may also contribute to the increase in mercury levels.

The presence of high mercury levels in narwhals can have detrimental effects on their health and behaviour. Mercury is a toxic heavy metal that accumulates in the body over time. It can impair cognitive functions, behaviour, and reproductive abilities. As narwhals are long-lived species with low reproductive rates, the impact of mercury accumulation can be particularly concerning for their overall population dynamics.

Moreover, human-made underwater noise pollution, such as that generated by shipping and seismic exploration, has been found to disrupt the feeding behaviour of narwhals. Studies have shown that narwhals decrease or even eliminate their buzzing rate (fast-clicking sounds made when searching for food) in response to underwater noise. This disruption during feeding can affect their body fat reserves, reproduction, and survival.

Oil and gas development

Firstly, the increase in shipping traffic causes more underwater noise pollution. Narwhals are very sensitive to noise, and it has been observed that they move away from their calving and feeding areas when large ships are present. As they depend on sound to communicate and echolocate, noise pollution can negatively impact their ability to find food and mates, navigate, and avoid predators. A study published in Biology Letters found that narwhals' buzzing rate, an indicator of feeding activity, declined by half when a ship was approximately 7.5 miles (12 kilometers) away and stopped entirely when the ship was within 4.3 to 5 miles (7 to 8 kilometers). This demonstrates the detrimental effect of noise pollution on their feeding behaviour.

Secondly, more shipping traffic increases the risk of collisions with these marine mammals, which are slow swimmers.

Thirdly, increased shipping brings a greater risk of oil or fuel spills, which can be devastating for the animals and humans that depend on these ecosystems. Oil spills in the Arctic are particularly concerning due to the lack of proven, effective methods for cleaning up oil in icy conditions. Oil trapped under sea ice may remain inaccessible until the ice melts, and response ships may struggle to manoeuvre in icy waters. An oil spill in Arctic waters could be catastrophic for sea life and the cultural livelihoods of indigenous communities who rely on the ocean for subsistence.

Furthermore, the infrastructure required for oil and gas extraction can also negatively impact narwhals. The construction of roads, pipelines, and buildings can degrade and destroy important habitats, migratory pathways, and biodiversity.

Overall, oil and gas development in the Arctic has far-reaching consequences for narwhals and other marine life, underscoring the importance of responsible development and the protection of sensitive areas.

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