The Greenland shark, known formally as Somniosus microcephalus, holds a distinction no other vertebrate can claim: it can live for centuries. These slow-moving predators glide through frigid Arctic waters at depths where sunlight barely penetrates, their biology fine-tuned for endurance in one of the planet’s harshest environments. Yet new research into their genetics and tissue chemistry suggests that the very longevity that makes them remarkable also makes them uniquely vulnerable to accumulating industrial pollutants, raising hard questions about whether human activity is quietly undermining an animal that evolution spent millions of years perfecting.
Eyes Built for Eternal Darkness
For decades, scientists assumed Greenland sharks were essentially blind. Most individuals encountered by researchers have milky, opaque corneas caused by a parasitic copepod that attaches directly to the eye. The assumption seemed reasonable: an animal living at extreme depths, frequently blinded by parasites, probably did not rely on vision. A genomic and transcriptomic study published in Nature Communications has overturned that idea. Researchers found that the visual system of the Greenland shark is not only intact but specifically adapted to function in dim light. The species retains functional genes for low-light vision, and histological analysis of retinal tissue confirmed the presence of structures consistent with a working visual apparatus, even in sharks whose corneas were compromised by parasites.
This finding matters beyond basic zoology. If Greenland sharks can see in near-total darkness, their foraging behavior likely extends across a wider range of deep-sea habitats than previously modeled. They are not passive scavengers drifting through the abyss but active hunters capable of tracking prey in conditions that would render most vertebrate eyes useless. The study also examined how the shark’s tissues maintain themselves over extraordinarily long lifespans, providing environmental context about the depths and temperatures these animals inhabit. For a creature that may swim the same cold corridors for four centuries, a functioning visual system is not a luxury. It is a survival requirement, and one that keeps the animal engaged with its environment in ways researchers are only beginning to appreciate.
Mercury in the Bones of a Living Fossil
While genomic research reveals what keeps Greenland sharks alive, a separate line of investigation exposes what may be slowly poisoning them. Mercury contamination in the Arctic has been a growing concern for years, with atmospheric deposition carrying the heavy metal from industrial sources thousands of miles away into polar ecosystems. A study published in Polar Science measured mercury levels across multiple tissue types in Greenland sharks, including cartilage, skin, and muscle. The research on mercury distribution in Greenland shark tissues found the contaminant present in all sampled areas, with the distribution pattern varying by tissue type. The study identified atmospheric sources as one pathway by which mercury enters Arctic waters, where it then moves through the food web and into apex predators like Somniosus microcephalus.
What makes this finding especially concerning is the intersection with longevity. Most fish accumulate mercury over their lifetimes through a process called bioaccumulation, where the metal builds up faster than the body can excrete it. For a species that lives only a few years or even a few decades, the total burden remains relatively contained. But a Greenland shark that persists for centuries has an almost unimaginable window for accumulation. Every meal, every breath of water passing over its gills, adds incrementally to a toxic load that the animal’s body may never fully clear. The Polar Science study discussed implications for the health and conservation of the species, framing mercury contamination as a pressure that could compound over the shark’s extreme lifespan in ways that shorter-lived species simply never experience.
When Adaptation Becomes a Liability
It is striking that the same biological traits that make Greenland sharks so resilient may also deepen their exposure to harm. Consider the visual system findings alongside the mercury data. If these sharks possess functional dim-light vision, they are likely active foragers in deep benthic environments where mercury-laden sediments concentrate. Their ability to hunt effectively in contaminated zones means more time spent in contact with polluted substrates and more consumption of prey organisms that have themselves absorbed mercury. In short, the adaptation that keeps them fed and alive could simultaneously increase the rate at which they ingest toxins. This is not a confirmed causal chain, but the logic follows directly from combining the two research threads: better vision leads to more effective deep-water foraging, which leads to greater contaminant exposure over a lifespan measured in centuries.
This dynamic differs from the threats facing other long-lived megafauna. Elephants and whales, for instance, face acute dangers like poaching, ship strikes, or habitat loss that can be addressed through targeted policy interventions. The Greenland shark’s problem is more diffuse. Mercury arrives in the Arctic from distant smokestacks and volcanic emissions, carried by atmospheric currents that no single regulation can fully control. The contamination is invisible, cumulative, and operates on a timescale that matches the shark’s own extraordinary biology. Reducing mercury emissions globally would help, but the metal already deposited in Arctic sediments and cycling through the food web will persist for decades. For an animal that measures its life in centuries, the pollution already present in its environment may represent a burden that cannot be reversed within any meaningful human policy horizon.
Gaps in What We Know
Despite these two significant research contributions, major questions remain unanswered. No primary longitudinal dataset currently tracks how mercury accumulation affects Greenland shark reproduction, growth rates, or behavior over decades. The tissue-level measurements from the Polar Science study provide a snapshot, but without repeated sampling of the same populations over time, researchers cannot yet determine whether mercury loads are increasing, stable, or approaching thresholds that trigger physiological harm. Similarly, reliable population estimates for Greenland sharks do not exist in the peer-reviewed literature. These animals live at depths and in regions that make systematic surveys extraordinarily difficult, and their slow metabolism and infrequent surface appearances mean that traditional fisheries assessment methods do not translate well.
The fishing threat also lacks strong primary documentation. Greenland sharks are known to be caught incidentally in deep-water trawls and longline fisheries targeting other species, but the scale of this bycatch and its population-level impact have not been rigorously quantified in institutional studies available for review. Without baseline population data, it is impossible to model whether current mortality from bycatch, combined with pollutant stress, is sustainable over the long term. The species’ extreme longevity complicates the picture further: a population decline might unfold so slowly that it would be nearly invisible on human timescales, even as it becomes effectively irreversible for the sharks themselves. This uncertainty leaves managers with little empirical grounding for setting protective measures, even as evidence mounts that the animals are living repositories of the Arctic’s industrial past.
Conservation in the Shadow of Deep Time
Protecting a creature that can outlive nations demands a different mindset than conventional wildlife management. Conservation frameworks are typically built around decades-long planning horizons, yet a single Greenland shark may experience several such cycles within its lifetime. The genetic insights into low-light vision and tissue maintenance suggest that these sharks evolved for stability: a slow, steady existence in an environment that, until recently, changed only gradually. Mercury contamination disrupts that evolutionary bargain by introducing a rapidly escalating stressor into a system calibrated for geological time. Even if emissions were drastically reduced tomorrow, the legacy of past pollution would continue to circulate through Arctic food webs, intersecting with shark lifespans that stretch far beyond any current policy commitment.
In this context, precaution becomes more than a slogan; it is a practical necessity. Regulators weighing industrial activities that increase mercury emissions, particularly in regions that feed into Arctic atmospheric circulation, are effectively making decisions that could shape the chemical environment of Greenland sharks for centuries to come. At the same time, filling the scientific gaps is essential. Expanded tissue sampling across age classes, improved methods for estimating population size, and better documentation of bycatch would all sharpen our understanding of how close this species might be to a tipping point. Until such data exist, the Greenland shark will remain both a marvel of biological endurance and a test of whether human societies can think and act on timescales that match the lives we are affecting, often without ever seeing them in the dark water below.
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*This article was researched with the help of AI, with human editors creating the final content.
