The parasite on a Greenland shark's eye is a pinkish-white copepod, a small crustacean called Ommatokoita elongata. It anchors itself to the cornea and leaves an opaque, damaged patch where it sits, which can impair vision in that eye. Older studies suggested it might blind the sharks, but a 2026 study of their eyes found that the retina is intact and the sharks still have working vision.
What Is the Greenland Shark Eye Parasite?
Ommatokoita elongata is a parasitic copepod in the family Lernaeopodidae. Reference sources describe it as pinkish-white and roughly 3 cm (about 1.2 inches) long, which makes it easy to spot against the dark eye of a shark that is several meters long. It is the only species in its genus.
It is not unique to the Greenland shark (Somniosus microcephalus). Researchers have also found it on the eyes of the Pacific sleeper shark (Somniosus pacificus) off Alaska, so it is a parasite of sleeper sharks in general, not of one species.
How Does It Attach to the Eye?
A study of six Greenland sharks from Victor Bay in Canada's Northwest Territories described the attachment in detail. Each adult female copepod, usually one per eye, was held to the cornea by an anchoring structure called the bulla, and each bulla sat over an opaque patch on the cornea. Some eyes also carried young copepodids, a larval stage, fastened by thread-like frontal filaments and linked to small opacities.
Under the microscope, the same eyes showed corneal ulceration, inflammation, and tissue damage, plus mild inflammation inside the eye (anterior uveitis). Exactly what the copepod eats is not well documented, but the damage suggests it feeds on or irritates the surface tissue it is anchored in.
Does the Parasite Blind Greenland Sharks?
Not completely, according to the most recent work. The picture has changed over time.
- Older view: The 1998 study concluded that the parasite could cause severe vision impairment, possibly including blindness. The authors also noted that the infected sharks looked otherwise healthy, so the infection does not seem to weaken them much.
- Typical impact: The Florida Museum notes that the copepod usually affects one eye and does not significantly harm the shark, since the shark does not rely on keen vision.
- 2026 study: Researchers examined the eyes of Greenland sharks over a century old and published the results in Nature Communications. The retina was intact, with no obvious degeneration. It is built almost entirely of rod cells, which work in dim light. The authors concluded that the sharks keep functional vision and rejected the idea that they are blind. They also found parasites attached at the edge of every cornea they analyzed, and the parasites are still thought to obscure vision where they sit.
The practical answer is that the parasite probably blurs or blocks part of what the shark sees, but the shark's visual system is not destroyed. Greenland sharks live in cold, dim water, usually deep, where eyesight is of limited use. They are slow swimmers that eat fish, other sharks, seals, and carrion. Like other sharks they also have a strong sense of smell, a lateral line that detects water movement, and electroreceptors, though no study has shown how much they lean on these senses to make up for eye damage.
How Common Is It?
Very common in the Arctic. The 2026 study reported that every shark cornea it analyzed had parasites bound to it, and a 2005 paper described blindness from this parasite as common in Arctic Greenland sharks.
There is one notable exception. When divers filmed Greenland sharks in the shallow St. Lawrence River in 2003, the sharks they saw did not show parasite-related blindness. They also showed display behaviors that had not been recorded in Arctic sharks. The authors suggested that better eyesight might let these sharks see one another and their prey more easily, but that is a hypothesis built on a small number of observations.
Exact infection percentages from older surveys could not be verified, so none are given here.
Does the Copepod Glow to Attract Prey?
In 1961, the Norwegian biologist Bjørn Berland proposed an idea: if the copepod were bioluminescent, it might act as a lure that draws fish toward the shark's face. In return, the shark would carry and shelter the parasite. That would make the relationship a partnership rather than pure parasitism.
The idea has not held up. The Florida Museum states that the claim of bioluminescence lacks scientific support, and no study has shown that the parasite gives the shark any benefit. On current evidence, the copepod gains a permanent perch and the shark gets damaged eyes.
Why Eyes Matter for Greenland Shark Age
The eye is also how scientists learned how long these sharks live. In 2016, researchers dated the eye lens nuclei of 28 female Greenland sharks using radiocarbon. The core of the lens forms before birth and does not renew, so it records the carbon chemistry of the shark's first years.
| Finding | Result |
|---|---|
| Shark lengths studied | 81 to 502 cm (about 2.7 to 16.5 feet) |
| Minimum lifespan | At least 272 years |
| Largest shark (502 cm) | Estimated 392 ± 120 years old |
| Age at sexual maturity | At least 156 ± 22 years |
This makes the Greenland shark the longest-lived vertebrate known. The popular figure of "over 400 years" is a rounded estimate for the largest animal, with a wide margin of error, not a measured age.
Greenland Shark Quick Facts
| Feature | Detail |
|---|---|
| Scientific name | Somniosus microcephalus |
| Typical adult length | 8 to 14 feet (2.4 to 4.3 m), with reports of up to about 21 feet |
| Range | Cold North Atlantic and Arctic waters, 1 to 12 °C (34 to 54 °F) |
| Depth | Surface to at least 1,200 m (3,937 ft), most often deeper in summer |
| Eye parasite | Ommatokoita elongata, frequently on one or both corneas |
| IUCN status | Vulnerable (assessed 2019) |
| Meat | Poisonous when fresh because of high urea and trimethylamine oxide levels |
Do not eat fresh Greenland shark meat. The toxins make it poisonous.
What Is Still Unknown
Most of the evidence comes from a small number of studies. The main ones are Berland's 1961 paper on the copepod and the shark's eyes, the 1998 and 2002 studies of eye lesions in Greenland and Pacific sleeper sharks, the 2005 St. Lawrence observations, the 2016 age study, and the 2026 vision study.
Open questions remain. It is still unclear how much the parasite reduces what a living shark sees, how much it affects feeding, and how the larvae find a host in the dark. Until that is measured, claims that the parasite lowers a shark's survival or hunting success are guesses.
Sources
- Ocular lesions associated with attachment of Ommatokoita elongata to corneas of Greenland sharks (Borucinska et al., 1998, record at AGRIS/FAO)
- The visual system of the longest-living vertebrate, the Greenland shark (Nature Communications, 2026)
- Vision and its relationship to novel behaviour in St. Lawrence River Greenland sharks (Canadian Field-Naturalist, 2005)
- Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Nielsen et al., Science 2016, via Oxford University Research Archive)
- Greenland shark species profile (Florida Museum)