【環境】プラスチック汚染がウミガメにもたらすリスクは若齢の個体ほど大きい

Younger sea turtles (juvenile and post-hatchling) are at a greater risk of dying from plastic ingestion than adult turtles, according to a study in Scientific Reports.

Britta Denise Hardesty and colleagues examined data from 246 sea turtle necropsies and 706 necropsy records from a stranding database. They found that juvenile turtles had ingested larger quantities of plastic than adults and that the amount of plastic in the turtles’ digestive tracts varied depending on their cause of death; turtles that had died from unknown causes had ingested the smallest amounts of plastic, followed by those that died from non-plastic related causes (such as boat strikes and drowning) while those that died from plastic ingestion had ingested the highest amounts. 23% of juvenile and 54% of post-hatchling turtles died of plastic ingestion had ingested plastic, compared to 15% of sub-adult and 16% of adult turtles. The count and mass of plastic ingested ranged from one to 329 pieces and weighed up to 10.41g. The findings suggest that feeding location and life history stage may impact the turtles’ risk of dying; younger turtles tend to feed in coastal waters drift with currents and feed in offshore waters closer to the surface, which are more likely to be contaminated with large plastic items that can accumulate in the animals’ digestive tracts, or cause perforation.

The authors found that the best way of modelling of the relationship between the amounts of plastic a turtle ingested and its risk of death took into account the number of plastic items in relation to the length of the turtle’s shell and its age. Their model represents a first step in quantifying the risk that plastic pollution poses to the world’s declining sea turtle populations, especially in coastal surface waters.