Greenland shark - Somniosus microcephalus
With an average adult length between 8 and 15 ft to a maximum of 24 ft, the Greenland shark is the Arctic’s largest fish. It is native to the north Atlantic and the Arctic and is the only shark to tolerate such temperatures throughout the year; its preferred range seems to be 30-50°F. It can be observed from the surface to depths of almost 7,218 ft. The Greenland shark is believed to be an opportunistic feeder and a scavenger primarily; if prey is too large to swallow whole, it is able to pin it in place with pointed upper teeth and cut round “plugs” from it with wide, curved bottom teeth by swinging its head in a circular motion. 90% of the observed Arctic population are host to the parasitic copepod Ommatokoita elongata, which consumes its corneal tissue and causes partial blindness, but its habitat and depths renders its sight useless. The only confirmed predator of the Greenland shark is the sperm whale, although it is also known to be cannibalistic in the presence of individuals deceased or in distress. Currently classed as Near Threatened and taken as bycatch, it has been historically targeted for its rich liver oil but the extremely high concentration of urea and trimethylamine oxide in its flesh renders it toxic. There is very limited data at present on its lifespan except for a single scientific paper that showed a size increase of just over 2 inches in 16 years on one shark; this growth rate suggests that a fully grown Greenland shark could be over 200 years old, potentially making it the longest-living vertebrate on the planet.