Contamination levels of mercury in the muscle of female and male spiny dogfishes (Squalus acanthias) caught off the coast of Japan

We analyzed the total mercury (T-Hg) and stable isotopes of 13C and 15N in the muscle of spiny dogfish (Squalus acanthias) caught off the coast of Japan. The average body length of the female spiny dogfish sampled (94.9 ± 20.2 cm, 50.5–131.0 cm, n = 40) was significantly larger than that of the males sampled (77.8 ± 10.8 cm, 55.5–94.0 cm, n = 35), although the ages of the samples were unknown. The T-Hg concentration in the muscle samples rapidly increased after maturity in the females (larger than about 120 cm) and males (larger than about 90 cm), followed by a continued gradual increase. Contamination level of T-Hg in female muscle samples (0.387 ± 0.378 μg (wet g)−1, n = 40) was slightly higher than that in male muscle samples (0.316 ± 0.202 μg (wet g)−1, n = 35), probably due to the greater longevity of females. In contrast, the contamination level of T-Hg in females smaller than 94.0 cm in length (0.204 ± 0.098 μg (wet g)−1, n = 20) was slightly lower than that in the males, probably due to the faster growth rate of females. Although the ∂13C and ∂15N values in the muscle samples increased with an increase in body length, there were no significant differences between the females (−17.2 ± 0.4‰ and 12.4 ± 0.9‰, respectively) and males (−17.3 ± 0.4‰ and 12.4 ± 0.8‰, respectively). A positive correlation was found between ∂13C and ∂15N values, suggesting trophic enrichment due to the growth.