The nurse shark: a quiet strengthWed 15 Feb, 2017
Among sharks living in the Caribbean Sea, the nurse shark (Ginglymostoma cirratum) is one of the most common species. These predators feed on small fish, mollusks or crustaceans. In addition to being completely harmless to humans, they play a particularly important role in regulating populations of their prey.
In order to better understand the role of these animals, researchers decided to study their metabolism. They captured eight young nurse sharks, all measuring around one meter long (adults can measure up to three meters). Brought back to the laboratory, each individual was placed in a respirometer, an aquarium in which the consumption of oxygen dissolved in the water is measured for a specified time, during which no exchange with the environment is possible. Such measurements lead to estimations of the quantity of oxygen necessary for the animals to ensure their basic metabolism, their consumption in the absence of any particular activity.
Different sessions of measurements were carried out day and night, to represent both the period of activity of the nocturnal sharks, and their period of rest. The results obtained represent the lowest oxygen consumption ever measured in sharks, at equal size and temperature. This record of tranquility could be due to the lifestyle of the species. Indeed, many sharks are forced to swim constantly, in order to create a current of water through their gills. Nurse sharks, however, are capable to pump water directly with their mouths, allowing them to breathe while being completely still. They thus have a particularly sedentary nature, resting all day in crevices and hunting at night. Intriguingly, despite this particularly low metabolism, nurse sharks grow and reproduce at similar speeds to other sharks. A mystery that requires further studies to be unveiled.
Whitney, N.M., Lear, K.O., Gaskins, L.C. & Gleiss, A.C. 2016. The effects of temperature and swimming speed on the metabolic rate of the nurse shark (Ginglymostoma cirratum, Boaterre). Journal of Experimental Marine Biology and Ecology, 477, 40-46.