Dusky Shark - Biology and Ecology

Biology and Ecology

As an apex predator positioned at the highest level of the trophic web, the dusky shark is generally less abundant than other sharks that share its range. However, high concentrations of individuals, especially juveniles, can be found at particular locations. Adults are often found following ships far from land, such as in the Agulhas Current. A tracking study off the mouth of the Cape Fear River in North Carolina reported an average swimming speed of 0.8 km/h (0.50 mph). The dusky shark is one of the hosts of the sharksucker (Echeneis naucrates). Known parasites of this species include the tapeworms Anthobothrium laciniatum, Dasyrhynchus pacificus, Platybothrium kirstenae, Rhynchobothrium ingens, Tentacularia coryphaenae, and Triloculatum triloculatum, the monogeneans Dermophthirius carcharhini and Loimos salpinggoides, the leech Stibarobdella macrothela, the copepods Alebion sp., Pandarus cranchii, P. sinuatus, and P. smithii, the praniza larvae of gnathiid isopods, and the sea lamprey (Petromyzon marinus).

Full-grown dusky sharks have no significant natural predators. Major predators of young sharks include the ragged tooth shark (Carcharias taurus), the great white shark (Carcharodon carcharias), the bull shark (C. leucas), and the tiger shark (Galeocerdo cuvier). Off KwaZulu-Natal, 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, the juvenile sharks have decimated populations of small bony fishes, with negative consequences for the biodiversity of the local ecosystem.