Total mercury in muscle tissue of five shark species from Brazilian offshore waters: effects of feeding habit, sex, and length.

This study was carried out to assess mercury levels in fish from Brazilian offshore waters. Generally sharks have relatively high mercury levels which are also affected by diet, age (associated with length), and sex. Total mercury levels were determined in five shark species with different habits (Carcharhinus signatus, Mustelus canis, Mustelus norrisi, Squalus megalops, and Squalus mitsukurii) which were collected during 1997 in southern Brazil's offshore waters. The highest mercury concentrations, all above the limit established by Brazilian legislation (0.5 microg.g(-1)), were detected in piscivorous species (C. signatus, S. megalops, and S. mitsukurii) with averages of 1.77+/-0.56, 1.9+/-0.58, and 2.22+/- 0.72 microg.g(-1), respectively, while species that feed mainly on invertebrates (M. canis and M. norrisi) had averages of 0.41+/-0.35 and 0.36+/-0.28 microg.g(-1). These results indicate that feeding habits influence total mercury level in sharks. Methylmercury (as a percentage of total mercury) determined in S. mitsukurii and M. canis also showed an influence of feeding habit. Positive correlations between mercury concentration and length were statistically significant (P<0.05) for all species, except M. norrisi. Although mercury levels were generally higher in males than in females for all species (with the exception of S. mitsukurii), a statistically significant correlation was observed only for M. canis.