Recently, there have been many changes in the Earth’s environment due to global climate change. Waters surrounding Korea are no exception to this trend. What are some of the impacts of climate change?

In its recent forecast for climate change, the National Institute of Meteorological Research announced that by 2050, there will be an 2.3℃ increase in global temperature, rainfall will increase by 3% and the sea levels will rise by 34cm. According to the forecast by the Korea Adaptation Center for Climate on the impact of climate change based on a temperature rise of 2℃, climate change will have a great impact on Korea’s natural environment, living environment, and industries.

In general, the primary concern in these reports relates to the direct damage to fishing and aquaculture industry from coral bleaching events in coastal areas as well as an increase in the number of large jellyfish. On the other hand, there is hope that aquaculture of warm temperate fish species such as tuna will become possible along the southern coast. More broadly, with the rise in sea temperature, warm temperate fish species are moving towards north, and cold water fish species are moving south.

In particular, the East Sea is considered a zone where changes in fish species from rising sea temperatures have the most serious impact. The appearance of subtropical fish species has continued since the 2000s. The rise in sea water temperature in the East Sea has become more distinct and the temperature has increased each year by 0.06℃ on average since the 1980s. This is a level that is 1.5 times higher than the average increase in global sea temperature of 0.04℃.

In 2007, a species assumed to be the Sokcho octopus, which can only be seen in subtropical areas, was caught in the coastal waters of Yangyang. Moreover, a large-sized whip ray and some 1,000 large-sized stingrays that weight up to 100 and 200kg have been caught in the coastal waters of Yangyang since 2005. Each of these events underscores the seriousness of subtropical fish species being observed in unusual places.

On the other hand, there is also a problem of cold current fish species swarming to warm seas where subtropical fish live.

According to the East Sea Fisheries Research Institute under the National Institute of Fisheries Science, 130,000 tons of pollack, a cold current fish species, were caught on average per year in the East Sea until the 1980s. However, in the current year, only 1 ton of pollack were caught, meaning that pollack have moved to other areas. Where pollack have left, squid, a warm current species, have filled in. The catch of squid last year recorded 170,000 tons, which is an increase of more than four fold over the past 30 years. Furthermore, there is a steady increase in the catch of winter species such as mackerel and saurel, with their distribution area rising northward.

Moreover, the coral bleaching events on coral bed in Jeju, the northward rise of blue crab fishing grounds from near Yeonpyeong Island to coastal areas of North Korea, and yellow corvine and hairtail which have moved from Jeju Island to shores of South Jeolla and South Gyeongsang Provinces are all a result of change in water temperature. The East Sea, which had created a balanced ecosystem with an appropriate mix of cold current and warm current fish species, is now being completely remapped in terms of fish environment as more warm current fish species are finding home there.

How should we respond to such changes in the marine environment from rising sea temperature? First, the private sector, academia, and the government must begin to closely observe these changes in order to fully understand them. Measures responding to these changes need to be established to counter global warming. Furthermore, efforts to reduce emissions of carbon dioxide must also be undertaken.

According to recent research, an extraordinary trend of cohabitation of cold current and warm current fish species in areas that are not boundaries of water masses has appeared in domestic littoral seas. This is because of the phenomenon that makes the sea temperature of the surface layer warmer and that of the bottom layer colder. In the research of sea temperature around the Korean Peninsula over 39 years (1968-2006) by the National Institute of Fisheries Science, it found that the temperature of the sea surface rose by about 0.93 degrees Celsius while that of the bottom layer of 100m in depth fell by 0.43 degrees Celsius. The research also cited the weakening of Siberian air mass as reducing the wind power at littoral seas of Korea by 30 to 40 percent, and accordingly, the role of the wind to mix the surface layer with the bottom layer also weakened. Taken together, these factors further contributed to a separation of changes in temperature by sea layer.

Due to this trend, warm current species such as mackerel, anchovy, and squid are concentrating in the surface layer while cold current species such as cod and herring are found in the bottom layer. Workers in the fisheries industry confirmed this trend anecdotally by reporting that while warm current species such as mackerel and anchovy have been rising steadily due to global warming, more recently, there is an abnormal trend of large amounts of cold current fish species being caught in the southern coast.

With the sea temperature rising rapidly due to global warming, the subtropical environment is expanding. This can be exemplified with the case of damselfish that have been found to spawn and hatch in seas near Jeju Island, and young fry that have hatched near Dokdo. Furthermore, there have been reports of a school damselfish, which can only be found in Jeju Island, near Dokdo. Although there have been reports of spawning protection activity of damselfish after their eggs have hatched, they had never been spotted in Dokdo before. Meanwhile, the neon damselfish, which is a warm current fish, have also been found near Dokdo.

Rising sea temperatures from global warming is clearly evident in the East Sea including Dokdo Island.