Blog Tags: Highly Migratory Species
Many marine species face endless obstacles: Overfishing, pollution, and habitat destruction are large threats, as well as climate change and its associated negative impacts. Factors ranging from their habitat, food source, predator defense, migration routes, and breeding grounds are already changing from warming seas, and these impacts are so widespread that it’s caught fisheries managers’ attention.
It might seem straight out of science fiction, but this story is real – radioactive tuna could be swimming in an ocean near you.
A new study found that after last spring’s Fukushima nuclear accident, Pacific Bluefin tuna caught off of San Diego appear to have been contaminated by radioactive materials from last spring’s nuclear accident in Japan.
The March 2011 earthquake and subsequent tsunami led to the meltdown of the Fukushima nuclear plant in central Japan. Even now, the only way to enter the zone 20 kilometers around the plant is with special government permission. After the accident, tests showed that concentrations of radioactive Cesium in coastal waters increased up to 10,000-fold.
This study, published in the Proceedings of the National Academy of Sciences, found the same radioactive Cesium in 15 Bluefin tuna specimens caught outside of San Diego. The fish tested showed a 10-fold increase from normal Cesium concentrations, well below the safety limit established by Japanese Ministry of Agriculture, Forestry, and Fishes.
Bluefin are a highly migratory species – they spawn in the West Pacific near Japan, then, once they have matured, may travel more than 9,000 miles to the East Pacific and the California coast. They’re such strong swimmers that the trip only takes a few months.
During the course of this trip, the radioactive concentration fell as the fish grew and the Cesium decayed. If they had tested tuna from Japan, the radiation would be expected to be up to 15 times more concentrated, according to Daniel Madigan, Zofia Baumann, and Nicholas Fisher, the co-authors of the study.
Monterey Bay Aquarium’s Seafood Watch already lists bluefin as a species to avoid due to severe overfishing and high mercury levels. They’re highly valued as sushi fish, which has led to a steep decline in their populations in both the Atlantic and Pacific oceans. Bluefin tuna are slow to mature, and are often caught before they have a chance to reproduce. Oceana is currently working to protect bluefin tuna from overfishing.
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