Tissue metal concentrations and antioxidant enzyme activity in western north Atlantic white sharks (Carcharodon carcharias)

Abstract

Anthropogenic practices have increased metal contamination in marine ecosystems. Most sharks have long lifespans, occupy an important ecological position at the top of marine food webs, and can accumulate metals. However, reference levels of metal contaminants in the tissues of sharks, particularly, apex predators such as the white shark (Carcharodon carcharias), are lacking. In this study, concentrations of copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), silver (Ag), and zinc (Zn) were measured in the muscle tissue of white (n = 42) and tiger (Galeocerdo cuvier; n = 3) sharks. Metal exposure in various species, including sharks, has been correlated with increased oxidative stress. Therefore, the main objectives of this study were to assess metal accumulation and antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)) in the muscle tissue of the population of white sharks and tiger sharks inhabiting the Western North Atlantic. The measured parameters were qualitatively compared between species. The small sample size of tiger sharks (collected from only one site) limited statistical analyses, therefore, white sharks were the primary focus of this study. Differences in tissue metal (Cu, Cd, Ni, and Zn) concentrations and antioxidant enzyme activities were detected based on collection site, with significant positive correlations between Cd and enzymes, SOD and CAT, and Zn and enzymes, SOD and GPx in C. carcharias. Differences in Ni concentration were detected based on sex, with females having higher Ni levels. Additionally, plasma osmolality was not correlated with tissue metal concentrations; however, osmolality decreased with increasing length in C. carcharias. This study is the first to report baseline levels of Cu, Zn, Cd, Ni, Ag, and Pb in muscle of North Atlantic white sharks and provides new insights into oxidative stress responses of these sensitive species to metal contaminants.

Keywords: Antioxidant enzymes; Metals; Muscle; Osmolality; White sharks.