Mercury Continues to be a Threat to the Conservation of Marine Mammals
Carin Wittnich*, DVM, MSc; Michael Belanger, ALAT; Nesime Askin, MSc;
Karim Bandali, PhD and W. Jack Wallen, PhD.
Heavy metal pollution tends to be persistent, have long lasting effects in the environment, and bioaccumulates up the food chain to affect the top predators. Relevant to wildlife conservation efforts, there are conflicting reports as to the effects of pollution by heavy metals such as mercury on species particularly pertinent to zoological parks and aquaria.
The total amount of mercury (mg/g wet weight) in livers of various marine mammals such as pinnipeds (seals: harp Phoca groenlandica; harbour Phoca vitulina; northern fur Callorhiinus ursinus; ringed Phoca hispida; Antarctic Artocephalus gazella), cetacea (dolphins: striped Stenella coeruleoalba; Risso’s Grampus griseus; bottlenose Tursiops truncates; white beaked Lagenorhynchus albirostris), and polar bears (Ursus maritimus) from different geographical locations around the world are reviewed spanning over 35 years.
Depending on the geographical location, species, age or sex, mercury levels vary from very low (0.05 mg/g Greenland seals) to very high values (700 mg/g Mediterranean dolphins). However, across all geographical areas, the mercury levels within species has either increased or at best remained unchanged over time. For example, in Greenland seals, mercury increased from 0.05 mg/g (1978-87) to 7 mg/g (1994-95). Mercury levels in seal pups from the East coast of Canada (1972-78) shows that their levels increased threefold over a 6 year period.
The world wide perspective of mean mercury levels in seals showed a dramatic increase to 25 mg/g by 1994. Dolphins in the waters around the United Kingdom have values which rose 12 fold from 1989 to 1998 (120 mg/g). In the Mediterranean, even in 1972, dolphins had high mercury levels (up to 700mg/g) and these continued to increase over time so that by 1996 levels reached up to 1100mg/g. As can be seen, many are showing levels which are well above the toxic level reported in dolphins of 50mg/g. Mean mercury levels in polar bears from Greenland have risen 2.5 times from 1983 to 1994, with some regions showing values as high as 26mg/g.