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.
Since our first post about the impacts of Japan’s nuclear crisis on the oceans, a lot has happened, but many questions remain and the situation is constantly changing.
As the cooling systems for the injured reactors at the Fukushima Daiichi nuclear power station remain offline, the method used to avoid a fire and full-blown meltdown of the reactors has been the continuous pumping of seawater onto the fuel rods.
Much of the seawater is evaporated, but thousands of tons of radiated water runoff have filled the nuclear plant. Tokyo Electric, who runs the facility, has shown extreme difficulties handling the growing amounts of radiated water.
They began pumping over 10,000 tons of seawater with lower levels of radiation out into the ocean, to make room for more contaminated water. Shortly afterwards a large crack was discovered last Saturday in a pit next to the seawater intake pipes at the No. 2 reactor which began leaking drastically higher levels of radiation directly into the Pacific.
During the leak, Tokyo Electric reported that seawater near the plant contained radioactive iodine-131 that was 5 million times the legal limit, and cesium-137 levels at 1.1 million times the legal limit.
Many of you have inquired via Twitter, Facebook and e-mail about how the Japanese nuclear crisis is affecting the oceans and marine life. There are still a lot of question marks, but here’s what our scientists have to say.
How it could affect marine life in general:
The greatest concern for marine life comes from the radiation from cesium, strontium and radioactive iodine entering the oceans via the smoke and water runoff from the damaged facilities. Small doses of radiation will be spread out over the Pacific Ocean, and monitors on the U.S. West Coast have even picked up slight traces of radiation from the smoke.
Although the levels of cesium and radioactive iodine in the immediate vicinity of the plant have increased and very small amounts of radiation have even been detected in local anchovies (1 percent of acceptable levels), it is not clear whether there will be any long-term or significant impacts on marine life off the coast of Japan or out to sea, according to researchers who studied the marine effects of fallout from nuclear weapons tests in the Pacific and the Chernobyl nuclear accident.