Did you know that the Nurse shark (Ginglymostoma cirratum) has the lowest metabolism of all sharks? It needs only 18% of the energy of the agile shortfin mako shark – while swimming. If it swims at all. It is nocturnal and spends the days lazily in its resting sites, together and sometimes on top of many other Nurse sharks.
Living in shallow coastal tropical and sub-tropical waters, nurse sharks are bottom-dwelling with two fleshy barbels on the lower jaw (chemosensory organs to help find prey hidden in the sediments). Or they form with their bodies fake caves for prey. These are then sucked in like with a vacuum cleaner. Due to their frugal life they don’t eat much – caught sharks more often that not didn’t have anything in their stomach.
Nurse sharks are brownish in color and reach 7 ft to 10 ft -2.2 to 3 m-, while females are longer than males. They are ovoviviparous, giving birth to 21–29 living young every two years. Like with dogs, scientists found DNA from up to 4 fathers in one litter. Nurse sharks frequent the same nursery and mating areas and resting sites nearby their whole lives (called strong site fidelity), makes them homebodies. They are shy and docile and despite their size no danger to humans, but when provoked, they can bite and are difficult to detach due to the suction.
It seems that the pacific subpopulation of the nurse shark is a species of its own (called Pacific nurse shark), restricting the nurse shark to Atlantic waters only (thus its new name Atlantic nurse shark). Since it doesn’t migrate I wouldn’t be surprised if the Eastern Atlantic subpopulation turns out to be a separate species, too. By the IUCN the Western Atlantic subpopulation is considered as Near Threatened, even as Vulnerable off South America. It is reported locally extinct in some areas off Brazil. Nurse sharks are hunted for their liver oil, fins, flesh and skin and juveniles also for private and commercial aquariums (despite their maximum size). When caught accidentally as bycatch, post-release survivorship is high. Habitat destruction endangers their nurseries and requires additional protective maesures (like in the Florida Keys).