The Caspian seal is endemic to the Caspian Sea. Over the past century, the seal population has significantly decreased, and the species is currently listed in the Red Book of the Russian Federation. Many factors adversely affect the state of the species, including the reduction of ice cover, habitat transformation, reduction of the food supply, animal capture, shipping, invasive species, etc. Pollution of the habitat also has a negative effect on marine mammals.
The staff of the IEE RAS, together with the I.D. Papanin Institute of Biology of Inland Waters (IBW RAS) and the Kazakhstan Agency of Applied Ecology (KAAE), checked the work on assessing the content of total mercury in the fur, vibrissae, and blood of Caspian seals. The assessment was carried out for live and dead (found dead) individuals of the Caspian seal, living in the northeast of the Caspian Sea (in the waters of the Republic of Kazakhstan) in the fall.
On average, the seal fur contained 2604 ± 1708 μg/kg mercury (n = 64), with a range of 258 to 8511 mg/kg. In the whiskers, the average mercury content was 3412 ± 1804 μg/kg mercury (n = 59), with a range of 984 to 12957 μg/kg. In the blood, the average mercury content was 114 ± 68 μg/L mercury (n = 59), with a range of 88 to 350 μg/L mercury. These concentrations are generally comparable with studies of other pinniped species.
No sex differences were found in the mercury content of the fur, whiskers, or blood. Age differences were found only in the analysis of fur: individuals aged 3+ years contained significantly more mercury than individuals aged 0-2 years.
In four of the studied individuals, the concentration of mercury in the fur exceeded the threshold values, which in other studies led to disturbances in the nervous system (>5400 μg/kg). However, in most of the studied animals, the detected mercury concentrations were below the values at which the effect on the body was recorded in other species of marine mammals.
The work was carried out with the financial support of North Caspian Operating Company N.V. and Kazakhstan Agency of Applied Ecology LLP. The authors express their gratitude to the management of the above-mentioned companies.
The work was published in the journal Marine Pollution Bulletin (Q1, IF = 5.3), Total mercury in fur, whiskers and whole blood of Caspian seals (Pusa capsica) from north-east of Caspian Sea (Kazakhstan).