Abstract
We analyzed Hg, Cd, Zn, Cu and Fe concentrations in liver samples as well as the Hg concentration and stable isotope ratios of carbon and nitrogen (δ13C and δ15N) in muscle samples from silvertip sharks (Carcharhinus albimarginatus) in Japan. Muscular and hepatic Hg concentrations increased with increased body length. However, these increases were more prominent in the liver than in the muscle samples, and appeared to occur after maturation. Hepatic Zn and Cu concentrations decreased during the growth stage, and then increased concomitantly thereafter with increases in Cd burden. Hepatic Fe concentration from males increased proportionally with increases in body length, whereas no increase was observed in samples from females, probably due to the mother-to-embryo transfer of Fe. The δ13C values tended to decrease with increases in body length, whereas no decrease in the δ15N values was observed.
Highlights
Marine predators, long-lived marine mammal and shark species, are known to accumulate high levels of mercury (Hg) which are biomagnified via the food web
We have previously investigated the Hg concentrations in liver and muscle samples from three shark species at different stages during their life span, and identified different patterns in Hg distribution: the Hg concentration in the liver and muscle samples of star-spotted dogfish (Mustelus manazo) increased markedly after maturation [7], the Hg concentration in the liver samples of spiny dogfish (Squalus acanthias) increased slightly with increases in body length, while that in the muscle samples increased markedly after maturation [8], and the Hg concentration in the liver samples of tiger sharks (Galeocerdo cuvier) increased markedly after maturation, while that in the muscle samples increased in proportion to body length [9]
According to Compagno et al [22], male and female silvertip sharks mature at about 1.60–1.80 cm total length (TL) and 1.60–1.99 cm TL, respectively, with a maximum body length of about 300 cm TL. These lengths correspond to precaudal length (PCL) of 1.2–1.4 m, 1.2–1.5 m and 2.25 m, respectively, based on the equation for the relationship between PCL and TL for the silvertip sharks analyzed in this study
Summary
Long-lived marine mammal and shark species, are known to accumulate high levels of mercury (Hg) which are biomagnified via the food web. The available data on the comparative Hg concentrations in the muscle and liver of shark species throughout their life spans are limited and somewhat inconsistent [7,8,9,10]. Branco et al [10] analyzed the Hg concentrations in liver and muscle of blue sharks (Prionace glauca) and reported similar levels of Hg in the liver and muscle that increased slightly with increases in body length: they did not observe any marked increases in Hg due to the formation of Hg-Se complexes. De Pinho et al [11] reported that the Hg concentrations in the muscle of five shark species increased with increases in their body lengths, but they did not determine the hepatic Hg concentrations Branco et al [10] analyzed the Hg concentrations in liver and muscle of blue sharks (Prionace glauca) and reported similar levels of Hg in the liver and muscle that increased slightly with increases in body length: they did not observe any marked increases in Hg due to the formation of Hg-Se complexes. de Pinho et al [11] reported that the Hg concentrations in the muscle of five shark species increased with increases in their body lengths, but they did not determine the hepatic Hg concentrations
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