Vertebrate Choice Project
| Rank | Classification |
|---|---|
| Common Name | Greenland Shark |
| Domain | Eukarya |
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Chondrichthyes |
| Order | Squaliformes |
| Family | Somniosidae |
| Genus | Somniosus |
| Species | Somniosus microcephalus |
Where Greenland sharks are found
Greenland sharks live in the cold North Atlantic and Arctic Oceans, around Greenland, Iceland, Canada, and Norway. They've also been spotted as far south as the Gulf of Mexico following deep cold currents (Edwards et al., 2022). They usually live between 100 and 1,200 meters deep and prefer water between -1.1°C and 7.4°C, in summer they go deeper to stay cold and in winter they come closer to the surface (Watanabe et al., 2012).
Greenland shark up close
Greenland sharks are the longest-living vertebrates with estimated lifespans of 272 to 512 years. They don't reach sexual maturity until around 150 years old. The freezing water slows down their metabolism so much that they age extremely slowly and they can go long periods without eating (Nielsen et al., 2016). They swim at only 0.34 m/s on average which makes them the slowest fish on record for their size (Watanabe et al., 2012).
Their flesh contains urea and trimethylamine N-oxide (TMAO) which act like antifreeze, keeping their cells and proteins stable in freezing water and under extreme pressure (MacNeil et al., 2012). This makes their meat toxic to eat raw, in Iceland the dish hakarl involves fermenting the meat for months to make it safe.
Most adults have a parasite called Ommatokoita elongata attached to their corneas which destroys their vision (Benz et al., 2002). They compensate with a strong sense of smell, a lateral line that detects pressure changes and ampullae of Lorenzini that sense electrical fields from other animals.
Greenland shark mating has never been directly observed due to their deep dark habitat. Females likely release pheromones to attract males from a distance and males use claspers which are modified pelvic fins for fertilization (Noell et al., 2020).
Greenland sharks have live birth. They're ovoviviparous so babies develop inside the mother using yolk for nutrients. Gestation is estimated at 8 to 18 years, litter sizes range from about 10 to potentially over 200 and pups are about 38-42 cm at birth (Nielsen et al., 2016; Noell et al., 2020).
Greenland shark in the deep ocean
As a cartilaginous fish their skeleton is made of cartilage not bone. They have a stocky body with a short snout, tiny eyes and small fins. Their upper 48-52 teeth are thin and pointy for gripping while the lower 48-52 are wide and flat for cutting (Yano et al., 2004; Compagno, 1984).
They have a stretchy J-shaped stomach for large meals and a spiral valve intestine that increases surface area for absorbing nutrients. Their large liver stores squalene oil for buoyancy and to eat large prey they bite down and roll their body to rip off chunks (Leclerc et al., 2012; Compagno, 1984).
They breathe through five pairs of gill slits. They also have spiracles behind their eyes that let them take in water without swimming, which helps since they spend a lot of time barely moving (MacNeil et al., 2012).
They have a two-chambered heart. Blood flows from the heart to the gills for oxygen then through the body and back. Their hemoglobin doesn't bind oxygen as strongly as warm-water sharks but cold water holds more dissolved oxygen so it works out (MacNeil et al., 2012).
Greenland sharks are solitary. Multiple sharks may gather at a food source like a whale carcass but they don't truly socialize, their movements are driven by water temperature and if they communicate at all it's likely through chemical signals (MacNeil et al., 2012; Edwards et al., 2022).
They cruise at 0.34 m/s and max out at 0.74 m/s which makes them the slowest fish on record for their size (Watanabe et al., 2012). They live in deep water where it's always dark so day and night don't really matter much, they move to shallower water in winter and deeper water in summer (Ste-Marie et al., 2022).
They eat fish like herring, salmon, cod and halibut, as well as marine mammals like seals and belugas and also squid. Some stomachs have even contained moose and reindeer remains which were likely carcasses that fell into the water. Young ones eat mostly squid and switch to fish and seals as they grow (Fisk et al., 2002; Nielsen et al., 2019).
They use suction feeding, expanding their mouth to create a vacuum that pulls prey in. For large prey, they bite down and roll their body to tear off pieces (Leclerc et al., 2012; Compagno, 1984).
They scavenge by following the scent of decaying flesh and actively hunt by ambushing resting prey. Seals sometimes sleep on the ocean floor and these sharks move slowly enough to approach undetected (Leclerc et al., 2012; Ste-Marie et al., 2022).