Oceans, which cover 70 percent of the Earth’s surface and are essential to humankind, are in a critical state. While fish stocks have plummeted due to over-fishing, pollution — especially plastic debris — is also taking a toll on marine animals, which ingest it or get tangled up in it.

When they met in Japan in May, the Group of Seven environmental ministers acknowledged that a form of plastic debris known as microplastics constitutes a threat to marine ecosystems. The World Economic Forum estimates that the total weight of microplastics in the oceans will top that of fish by 2050.

It is also feared that an increased concentration of carbon dioxide in the atmosphere — though to be as a main source of global warming — will acidify the oceans as well as raise their temperature.

Since Japan consumes large volumes of fish, including one-fifth of the global tuna catch, and has vast expanses of exclusive economic zones in its surrounding seas, it has both a practical and moral obligation to promote global efforts to protect the oceans by working out concrete and effective measures to fight marine pollution.

The dwindling of fish stocks is alarming. According to a 2014 report by the U.N. Food and Agriculture Organization (FAO), the share of wild fish stocks that are overexploited is rising. While the share was 10 percent in the 1970s, it rose to 29 percent, a biologically unsustainable level, in 2011. On the contrary, the share of fish stocks that can be safely harvested in greater amounts declined from 40 percent to 10 percent over the same period.

One of the causes of the depletion is illegal, unreported and unregulated (IUU) fishing. The FAO estimates that the size of IUU fishing is as large as 26 million tons per year and is worth $23 billion. It views the practice as one of the greatest threats to marine ecosystems. It would be safe to assume that the Japanese people consume a large amount of IUU-caught marine products.

Another threat is ocean acidification. As the carbon dioxide concentration in the atmosphere rises, more of the gas finds its way into the oceans, increasing their pH levels. Due to human activities, the atmospheric CO2 concentration increased from the pre-industrial level of 280 parts per million to 400 ppm today. Acidification negatively impacts various types of marine animals.

Microplastics — defined as plastic particles less than 5 mm in diameter — also pose a threat to the ecosystems. Some have a diameter of less than one-thousandth of one millimeter. When exposed to ultraviolet rays in strong sunlight or repeatedly beaten by waves, plastic waste drifting in the sea such as PET bottles and plastic wrapping decays and breaks up into tiny pieces of microplastics. Microplastics also originate in chemical fibers, dish washing sponge made of melamine resin and facial scrubs and cosmetic products that use small particles of polyethylene called microbeads.

Microplastics are often consumed by fish and sea birds and absorbed by shellfish. Scientists warn that the microplastics ingested by marine animals adversely affect their health and they may ultimately impact the health of the people who consume them. According to the Environment Ministry, the amount of microplastics in the seas around Japan was 27 times higher than the global average last year. Japanese consumers should be aware of the risks posed by seafood contaminated by microplastics.

Larger plastic waste is also polluting the sea, such as intact PET bottles, plastic bags distributed by retailers, fishing nets and bobbers, and Styrofoam products. Plastic bags are sometimes found in the stomachs of dead turtles. Some seals die when plastic bands to hold together beverage cans or fishing nets coil around their necks.

Some plastic particles absorb sea-borne pollutants, including carcinogenic and highly toxic PCBs (polychlorinated biphenyls) — widely used mainly in high voltage condensers and transformers until the 1970s — and PBDEs (polybrominated diphenyl ethers) — used as flame retardants and affecting thyroid functions.

Last month, the FAO Agreement on Port State Measures to Prevent, Deter and Eliminate Illegal, Unreported and Unregulated Fishing went into force after ratification by 29 parties including the United States, the European Union, Australia, New Zealand, Cuba, Norway and South Korea — but not Japan.

The agreement is designed to block the flow of IUU-caught fish into national and international markets. Under the treaty, foreign vessels will provide advance notice on such matters as marine products on board before requesting permission for port entry. If the parties to the treaty suspect that the vessels engaged in IUU fishing, they can deny access to ports or inspect the ships. Information on suspicious vessels will be shared by all parties to the treaty.

Japan should accelerate its efforts to implement measures required to comply with the treaty so it can ratify it.

In its upcoming review of the nation’s Basic Plan on Ocean Policy, the government should make measures to protect oceans and maintain sustainable use of marine resources the policy’s main pillar. It also should strive to reduce plastic waste. One way would be to require all stores to charge a fee for plastic bags at the checkout counter — a step that would encourage shoppers to switch to reusable bags. Consumers can also help by buying products using paper and glass packaging when possible.

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