After introducing the homebody Atlantic nurse shark last week, this weeks shark is the opposite: the Dusky shark (Carcharhinus obscurus). It can be found worldwide in warm waters along the coasts (and offshore following ships, too) of America, Australia and Africa (and parts of Europe and Asia). It is nomadic and strongly migratory (even if genetic tests suggest that Indonesian and Australian Dusky sharks represent distinct populations) and wanders seasonally (between the poles in the summer and the equator in the winter) up to 2,400 mi – 3,800 km.
Despite being one of the largest members of the requiem sharks (it reaches on average 10 ft -3.2 m- and up to 14 ft -4.2 m- in length) and having a (maximal of all tested sharks) punctiform bit pressure at the tooth tip of 60 kg (just like human bites, by the way), the Dusky shark is no danger to humans (the very few unprovoked attacks attributed to this species are most likely cases of mistaken identity).
Being apex predators, Dusky sharks are one of the slowest-growing and latest-maturing sharks, not reaching adulthood until around 20 years of age. Female dusky sharks are ovoviviparous and give birth to at most one litter of 6 to 12 young every three years. They use shallow inshore habitats as nursery areas, since juvenile Dusky sharks (in contrast to their parents) do have natural predators, namely other large sharks. Off KwaZulu-Natal (South Africa), the use of shark nets to protect beaches has reduced the populations of these large predators, leading to a dramatic increase in the number of juvenile Dusky sharks (a phenomenon called “predator release”). In turn, these juvenile sharks have decimated populations of small bony fishes, causing monocultures of small Dusky Sharks.
Nevertheless, due to their very low intrinsic rate of increase (renders them among the most vulnerable of vertebrates) and fishing pressure Dusky sharks are considered Vulnerable worldwide and Endangered in the Northwest and Western Central Atlantic. They are targeted for highly valued fins, meat, liver oil and skin and have a high mortality rate when taken as bycatch.