Today we will investigate the attributes of the Dusky shark (Carcharhinus obscurus). Dusky Sharks are also known as a “requiem shark”, which means they are migratory, live young-bearing sharks usually in the family Carcharhinidae. They are typically found in tropical and temperate waters throughout the world. These coastal pelagic sharks migrate to higher latitudes during the warmer months and to central latitudes in cooler months (see figure 1). Their migration routes can span a distance of up to 1000 miles and are undertaken at different times by males and females.
Studies have shown that female Dusky Sharks return home to where they were born to birth their pups (6-12 per litter). The gestation period for this shark 16 months. The growth rate of Dusky Sharks is very slow. They can live up to 45 years and do not reach reproduction age until 20 years. This could be one of the reasons that the Dusky is listed as a vulnerable species on the IUCN Red List of Threatened Species.
Dusky Shark numbers have decreased throughout the years. Populations that live in the Northwest and Western Central Atlantic had an initial decline due to fishing in the 1970’s (like most shark species, they were fished mostly for their fins, as well as other parts that could be derived for commercial goods). In the 1980s, the US fisheries expanded, resulting in a quicker and more drastic population decrease. In 2000, regulations were implemented to protect the Dusky Sharks in US Atlantic waters. From the prime unregulated fishing era of the 1970s-2000s, Dusky Shark populations decreased by 62-92%. Though fishing regulations helped counteract the threats to Dusky Shark populations, bycatch is suspected to be another reason for this sharks decline. Management plans in the US declare that any dusky shark that is caught in bycatch must be released with little harm and without taking the shark out of the water. It is difficult to say if these mandates have been effective and more studies need to be done to see if they have helped the species survive to maturity.
Join us next week as we learn about another amazing shark species.
Edited By: KC O’Shea
Photography by: Richard Ling
Tricas, Timothy C., Kevin Deacon, Peter Last, John E. McCosker, Terence I. Walker, Leighton Taylr. A Guide to Sharks & Rays. San Francisco: Fog City Press, 2002. Print.