Abstract and Main Objectives: The Greenland shark (Somniosus microcephalus) is one of the largest shark species, reaching lengths in excess of 550 cm (1,500 kg body mass) and is one of a few species of sharks that inhabit polar waters year-round. In general, their distribution spans from the Northern Atlantic Ocean to the Arctic where they inhabit inshore and intertidal areas during the cold months, but migrate to deeper waters (>2000 m) during the warmer months. Although at the beginning of the 1900’s Greenland sharks were targeted in the large-scale fisheries for their liver oil, reaching annual landings of more than 30,000 individuals, these commercial fisheries ended in the 1960’s.
Currently, Greenland sharks are still incidentally captured in Arctic waters by several large commercial fisheries (e.g., long‐line for halibut and trawling for shrimp). Compared to many other sharks, the life‐history of the Greenland shark remains largely unknown, though recent work has shown them to be very slow growing, late to sexually mature, have long gestation times, and have a relatively low number of offspring. For example, females reach maturity at a length of 450 cm at an age of more than 100 years, their somatic growth may be as slow as 1 cm per year, and they give live-birth to approximately 7-10 young after a gestation period lasting between 1 and 2 years. Overall, the size, age, and population genetic structure of Greenland sharks in the North Atlantic and Arctic is unknown, and given the low reproductive capacity, it is reasonable to consider them vulnerable to overfishing. Taken together, the unique life-history of Greenland sharks combined with a general lack of knowledge on their movement ecology and population status has led them to be classified as “Near threatened” by the International Union for the Conservation of Nature, hence making our proposed research on this species very timely.
Our current focus, therefore, is centered on trying to elucidate the Greenland shark’s reproductive habits, migratory patterns, and distribution. During the planned 8-day research cruise on RV Dana we will collect shark specimens in Bredefjord, an area that holds the best promise to capture, tag, and release as many reproductive age sharks as we can find. Our past experience working with Greenland sharks has shown that once the sharks are brought to the surface, we can easily restrain them in the water to obtain precise measurements and to attach tags. This boat-side scenario also offers a unique opportunity to determine their actual reproductive status (e.g. presence of oocytes, fertilized eggs, pups) via our newly acquired portable Ibex Evo ultrasound machine which is used by veterinarians to visualize reproductive systems in large animals. In addition, blood samples will be collected for subsequent analysis of reproductive hormone (e.g. estrogen, progesterone) levels in order to determine the state of sexual maturity of each individual.
Further links & information: “Old and Cold” website: http://bioold.science.ku.dk/jfsteffensen/OldAndCold/
Two informative pieces can be found at the following links: https://www.saveourseasmagazine.com/the-oldest-on-earth/ & https://www.newyorker.com/tech/annals-of-technology/the-strange-and-gruesome-story-of-the-greenland-shark-the-longest-living-vertebrate-on-earth