Written by Jetty (Jett) Porter, Undergrad Student, University of Miami RSMAS & Intern. Image Andy Murch
Wrong Temperature? No energy!
Oceanic Whitetip sharks are known pelagic migratory predators, meaning that they spend a large majority of their lives in open water, away from shore. As ectotherms, animals who don’t control their internal body temperature, they need to regulate their temperature by moving to warmer or colder elevations. This helps keep their temperature optimized for their metabolism which is their ability to digest food and convert it into energy needed for movement, hunting, etc. These sharks have high metabolic rates, and burn large amounts of energy to find prey. Prey density in the open ocean is low, and their next meal may be days away at any given time, so they must be careful and strategic with how they regulate their temperature in order to survive efficiently in open ocean conditions. Keep in mind that most open water sharks must move constantly to breathe, a process called ram ventilation, so stretching their metabolism as far as possible is extremely important.
Up and Down the Whitetips Go
Researchers tagged 16 Oceanic Whitetip sharks around Cat Island, Bahamas with satellite tags that recorded both their temperature and elevation in order to find out how these sharks efficiently manage their internal temperatures. It was found that these sharks do indeed alter their vertical migration behavior to match seasonal temperature variation. This means that they move up and down to warm up or cool down when they are at an unfavorable temperature. In the warmer months, when temperatures exceeded 82.4oF (28oC) they reduced the amount of time spent in the upper 160 feet (50m) of the water column, and likewise lengthened the time it took them to ascend to the surface when they did choose to hunt at the surface. When the sun is out, the sharks decide that “this water is too hot!” and travel to deeper, cooler waters. In the winter months, the water column was cooler, generally below 82.4oF (28oC), and more evenly mixed, so the sharks spent a greater amount of time at the surface, and decreased vertical migrations below the upper 160 feet (50m), essentially deciding that the deeper water is now too cold.
What water temperature is “just right”?
From this research it is clear to see that the optimal metabolic temperature for Oceanic Whitetip sharks is somewhere below 82.4oF (28oC), and that they change their behavior as the seasons and temperatures change to occupy this optimal range year-round. It has been found that they prefer water temperatures between 68oF (20oC) and 82.4oF (28oC).
Citation: Andrzejaczek, S., Gleiss, A.C., Jordan, L.K.B. et al. Temperature and the vertical movements of oceanic whitetip sharks, Carcharhinus longimanus. Sci Rep 8, 8351 (2018).