Mercury, cadmium, zinc and copper concentrations and stable isotope ratios of carbon and nitrogen in tiger sharks (Galeocerdo cuvier) culled off Ishigaki Island, Japan

Metal Concentrations in the Liver and Stable Isotope Ratios of Carbon and Nitrogen in the Muscle of Silvertip Shark (Carcharhinus albimarginatus) Culled off Ishigaki Island, Japan: Changes with Growth

“…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 ]. On the other hand, 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.…”

“…The Hg concentration in the liver and/or muscle is generally higher in males than in females of similar body length, and the marked increase in Hg in the liver and/or muscle after maturation generally proceeds more quickly in males than in females due to the faster growth and earlier cessation of maturation in the males of species such as spiny dogfish [ 8 , 13 ], shortspine dogfish ( Squalus mitsukurii , [ 14 ]), star-spotted dogfish [ 7 ] and several shark species [ 15 ]. In contrast to most shark species, the growth rates of male and female tiger sharks are reported to be similar [ 16 ], and the body lengths of males and females, reflected in the marked increases in Hg in the liver after the maturation, are also similar [ 9 ].…”

“…We previously speculated that liver lipid content and liver size could affect Hg distribution, as Hg may be sparingly distributed in organs containing large amounts of lipids [ 7 , 17 ]. As part of our investigation of the factors affecting Hg distribution in shark species, we have analyzed the amount and composition of liver oils (color) as well as liver size [ 7 , 9 ] to clarify the above-mentioned three patterns of Hg accumulation in the liver and muscle observed among spiny dogfish, star-spotted dogfish and tiger sharks. However, we have not yet identified the factors affecting Hg distribution.…”

“…Cadmium (Cd) is accumulated in the liver of tiger sharks in a body length (age)-dependent manner [ 9 ]. On the other hand, essential metals, such as zinc (Zn) and copper (Cu), in the liver of tiger sharks decrease during the growth stage, and then increase with a concomitant increase in Cd burden after maturation.…”

“…We analyzed the stable isotope ratios of carbon and nitrogen, generating delta notation values (δ 13 C and δ 15 N), in muscle samples of three shark species in order to compare their ecology. The relationships between the δ 13 C or δ 15 N value and body length in spiny dogfish [ 8 ] and star-spotted dogfish [ 7 ] differed from those in tiger sharks [ 9 ]: both the δ 15 N and δ 13 C values in the spiny dogfish and star-spotted dogfish increased with increases in body length (growth), while those in tiger sharks decreased. The increases in the δ 15 N and δ 13 C values due to growth in the spiny dogfish and star-spotted dogfish may be explained by growth-related increases in their trophic levels [ 7 , 8 ], while the decreases in the δ 15 N and δ 13 C values with growth in the tiger shark may be explained by a shift from coastal to pelagic feeding [ 9 ].…”