World's Oldest Living Vertebrate Makes Rare Appearance on Camera
Scientists have captured some very rare footage of Greenland sharks during a research project into population distribution in the Candian Arctic.
Brynn Devine and Jonathan Fisher, researchers at the Fisheries and Marine Institute of Memorial University of Newfoundland, embarked on a project in 2015 to study the distribution of the little-known shark in the Canadian Arctic. Although the shark was caught in great numbers by Greenland and Norwegian fisheries during the first half of the 20th century, little research has been carried out into the species, hence the extent of its distribution throughout the polar region remains largely unknown.
With Arctic ecosystems facing an uncertain future through the effects of climate change, plus the problems associated with population decline through bycatch as a result of industrial fishing operations, according to the report, published in the online journal Nature, 'the paucity of data concerning [body size and survival traits] and Greenland shark population dynamics has led to its designation as ‘near threatened’ or ‘data deficient’ throughout parts of its range; in other areas, it remains unassessed. Therefore an urgent need exists to address major knowledge gaps concerning past, present, and potential future population dynamics'
Greenland sharks (Somniosus microcephalus) are the oldest living vertebrates known to science, however, there is so little data available regarding their lifespan that the female specimen used to determine the species' age was documented as 392 ± 120 years, meaning it could have been as 'young' as 272, or as old as 512 years of age. They reportedly grow at less than 1cm per year, and are thought to not reach sexual maturity until they are at least 100 years of age.
They are some of the biggest sharks in the ocean, growing to over 6m in length, possibly more, with the largest specimens weighing in at over 1000kg, although their average length is estimated to be between 3-5m, with a weight around 400kg. Despite their large size, they are difficult to study as – like the recently identified new species of sixgill shark – they inhabit deep waters, having been observed at depths of up to 2,200m. They are apex predators, feeding on fish and rays and even small sharks, as well as scavenging the remains of polar bears, moose and reindeer. They have been reported to hunt live seals, but as the Greenland shark is an incredibly sluggish swimmer, scientists remain unaware as to how they would capture one of the fastest and most agile animals found in the sea.
During the study, cameras baited with squid were deployed during the summer months of July-September in 2015 and 2016. Out of the 31 camera deployments that were made, a total of 142 individuals were identified, and although none of them was observed during more than a single deployment, as many as 18 sharks were recorded in the same area at the same time. The researchers used their findings to calculate estimates of Greenland shark abundance and biomass based on the time it took sharks to arrive on the scene, along with swimming speed and body length derived from laser photogrammetry, observed from the video.
The report concludes that 'Greenland sharks are seemingly widespread and commonly inhabit a wide range of depth and temperature conditions,' however it 'represents the first step towards closing a major knowledge gap on the population status of the Greenland shark.'
Brynn Devine and Jonathon Fisher's report is published in online scientific journal The Conversation. The full report, authored by Brynn M. Devine, Laura J. Wheeland and Jonathan A. D. Fisher is available at Nature.com, and both are published under the Creative Commons Attribution 4.0 International License