A new study highlights the impact of metal accumulation (cobalt, manganese, nickel, copper, iron and mercury) on the health of twenty individual sharks representing 8 species that were accidentally caught by fisheries in Brazil. Necropsies of the animals showed high levels of metals in the liver, gills and rectal glands. Perhaps not surprisingly, larger animals had more accumulation of the metals in their gills than smaller animals. Higher accumulation in larger (and hence older) animals may be due to reduced elimination and higher lifelong exposure to metals as the animals age.
Interestingly, they found lower levels of nickel and iron in the liver of the older animals. As nickel is important for energy metabolism and endocrine function, it is possible the lower levels reflect higher use of this metal. Although these particular metals were lower in the liver, the concentration of metals were highest in this tissue as well as the rectal gland. As levels were lowest in the muscles and gills, specifically, this suggests that the animals had ingested the metals from their diet as opposed to absorbing them through the gills from the surrounding water.
Cobalt accumulation in the liver was associated with high levels of ALT activity, a marker of liver damage. The high levels of iron and mercury were also associated with increases in markers of liver and kidney damage as well as increases in circulating triglycerides showing altered fat metabolism. In addition, the accumulation of metals in the gills was found to be associated with markers of impaired acid-base regulation and urea. Overall, these types of physiological disturbances can impact the health of a species and are thus important for shark conservation efforts.
Wosnick N, Niella Y, Hammerschlag N, Chaves AP, Hauser-Davis RA, Rocha RCC, Jorge MB, Oliviera RWS, Nunes JLS. Negative metal bioaccumulation impacts on systemic shark health and homeostatic balance. Marine Pollution Bulletin. 168: 112398, 2021.