Scientists from the Florida Program for Shark Research got more than they bargained for when they recently encountered a ‘monster’ shark that was bigger than their submarine. The shark was a bluntnose sixgill, an ancient species that can grow over 16 feet long and weigh more than a ton. Living in tropical waters around the world, the bluntnose typically live at depths between 650 and 3,300 feet, making it difficult for researchers to learn about and protect the species. However, as commercial fisheries cast deeper into the ocean, deep sea sharks like the bluntnose are being increasingly caught as bycatch.
In an effort to conserve the species, researchers began investigating whether these sharks would die if released after being caught. Initially, the sharks were brought to the surface and tagged, however the data garnered from these efforts showed an interesting trend. Every day and night the bluntnose consistently migrate vertically, staying closer to the surface during the night and moving thousands of feet deeper at dawn. For the first two days after being brought to the surface and tagged, however the sharks broke this pattern and behaved more erratically. Scientists theorized that the two day behavioral change represented a recovery period due to the short term physiological stress resulting from being captured and brought to the surface.
In order to combat the effects of surface tagging, researchers pivoted and began making attempts to tag the sharks at depth using a submarine. It was during one of these expeditions that the team captured video of the massive shark. After some trial and error, the team was eventually able to successfully tag a bluntnose. The tag will remain on the shark for three months before detaching. Once the detached tag floats to the surface, it will upload its recorded data via satellite link for analysis. Scientists expect to see the vertical migration pattern without the two day recovery period, but they won’t know for sure until the tag resurfaces.