Microplastic ingestion by sea turtles around Tokyo Bay: Level of water pollution influences ingestion amounts.

We investigated the contents inside the esophagus and stomach of turtles inside and outside of the Tokyo Bay area, which face high and low risks of microplastic (MP) exposure, respectively. 65 synthetic particles were recovered from 8 out of 22 turtles, using ATR-FTIR followed by density separation with calcium chloride solution. Statistical analysis indicated that turtles in high-risk areas ingested significantly more MPs than those in low-risk areas. As the inflow of MPs from major rivers influences pollution levels in the ocean, the results of this study highlight the importance of major rivers for MP ingestion by turtles. Additionally, we discussed the current methodology's shortcomings and addressed scope for subsequent research, along with suggestions on future conservation.

Mercury bioaccumulation and trophic transfer in Pacific Saury from the North Pacific Ocean.

This study investigates mercury (Hg) dynamics in Pacific Saury (Cololabis saira) across the North Pacific Ocean, specifically off East Japan in 2018. Saury traits vary with total mercury (THg) concentrations in muscle tissues ranging from 0.017 to 0.082 µg g-1 w. w., averaging of 0.042 (n = 46). A positive correlation between THg and saury length (Knob length, 270-319 mm) indicates increased Hg concentration with size. Stable isotopic tracers suggest Pacific Euphausiids (Krill) are significant contributors to the saury diet (>70% of total). Significant correlations between logarithm THg concentration (Log THg) and δ15N (‰) (R2 = 0.70) demonstrate Hg trophic biomagnification, with regional variations. Comparative analysis between the eastern (ENPO) and western North Pacific Ocean (WNPO) indicates differences, with WNPO saury exhibiting lower δ15N values and higher THg levels than ENPO saury. This suggests that the WNPO, located near East Asia, the world's largest Hg emitter, experiences elevated Hg levels in seawater due to anthropogenic release. Overall, this study advances understanding of Pacific Saury's ecological interactions and Hg bioaccumulations, emphasizing the importance of species-specific behaviors and regional influences in ecological studies.