Did you know that the shark fisheries off northeastern Brazil catch nearly solely sharks containing dangerous amounts of mercury? 90% of the caught sharks and rays are Night sharks (Carcharhinus signatus), a deepwater species that migrate vertically from as far down as 1.2 mi -2 km- at day to within 85 ft – 26 m- of the surface at night (thus the name). It lives on the outer continental shelfs and upper continental slopes on both sides of the Atlantic Ocean.
The Night shark is a slender, fast shark and reaches usually a length of 6.6 ft -2 m. It has a long pointed snout and large green eyes. Like all requiem sharks it is ovoviviparous and gives birth to 4–18 living young measuring 20 to 28 in -50 to 72 cm- after a gestation period of 1 year. Each embryo has a separate compartment within one of the two uteruses and is nourished by a yolk sac and later through a placental connection. Males mature at an age of 8 years and females at an age of 10 years.
Being a target species for its highly prized fins and meat, but also for liver oil and fish meal, the Night shark is caught commercially and as bycatch. It it is the most abundant elasmobranch species in the seamount fisheries off Brazil, yet. Formerly common in Caribbean, Cuban and U.S. shark fisheries, fishing pressure resulted in a substantial decline there, too. That’s why the IUCN has assessed the Night shark globally as Vulnerable, even if the U.S. fishing ban seems to work there.
Given that the caught Night sharks off Brazil are mostly juvenile (I think that the shallow banks off Brazil are nursery areas for Night sharks), it is all the more alarming that the caught sharks contained mercury levels higher than allowed by the Brazilian laws (and WHO recommendations) – what amount of mercury would adult sharks contain since they have more years to accumulate it?