Q. Why Korean Freshwater Fish Fauna have such an interesting distribution?
South Korea has 192 native species of freshwater fish, Of which 76 are catadromous, anadromous, or marine species. Some of these 192 native species, excluding 55 South Korean endemic species, are also distributed in Amur River, Chinese river systems(ranging from Liaohe River in Liaoning Province to Jiujiang River at Gwangdong Province along the chinese east coast), and Japan. 18 are not distributed in Amur River but in Chinese river system and 5 are vice versa. Why Korean Freshwater Fishes have such interesting distribution?
KOR Pen., "Hwanghe - Amur Border"
During the last Great Ice Age, from 15,000 to 11,000 years ago, sea level was much lower than today. Because the areas covered in ice and snow were limited to chinese upper river regions, freshwater fish were not isolated on certain refuges. This is one of the reasons why Northeast Asia has a lot of freshwater fish species compared to other cold temperate and temperate regions.
Paleo Hwanghe River Drainage was ranging south to southern Taiwan, east to southwestern Japan, north to western Heilongjiang Province in China, and west to Tibet.
The followings are tributaries to Paleo Hwanghe River :
Hwanghe River drainage, all streams in Yellow Sea slope(excluding Apnok River in N.Korea), South Sea slope, southwestern Japan, Nunjiang River(now a tributary to Amur River) in Heilongjiang Province of China, and Changjiang River-3rd longest river in the world. <Go to Korean 'A' Region!>
Paleo Amur River, now the 9th longest river in the world, had a huge freshwater lake, originated by Korean Peninsula-Japanese Islands' tectonic separation, in lower river region.
The followings are tributaries to Paleo Amur River:
Amur River drainage(with the exception of Nunjiang River), all streams in East Sea(Sea of Japan) slope including eastern Korea, northwestern Japan, Russian Far East, and western Sakhalin Island, and Apnok River(now a river in Yellow Sea slope).
<Go to Korean 'B' Region!>
Regions now separated by seas were linked with land and freshwater lakes and rivers. Therefore, freshwater fish were able to enter adjacent freshwater streams and colonize them in any rivers, lakes, and swamps in these large river systems. Of course, they would not colonize all tributaries.
As the last Ice Age ended up ice and snow melting and rising sea level, the large parts of lower river regions became no more freshwater passages. After Mt.Baekdoo was erupted several times and Bohai Bay that had been uplifted subsided, allowing the sea to create present day's Bohai Bay. Apnok River running into Amur River at that time changed its way of flow southward. Also, by activated ancient faults in the central Heilongjiang Province, Nunjiang River which flowed southward into Liaohe River changed its way of flow into Amur River. Some species of freshwater fish, distributed in Amur River system, Yellow and South Sea slope including China and Koreas, or in Amur River system, and Yellow and South Sea slope only in Korean Peninsula, would pass from Amur to Yellow and South Sea slope or vise versa.
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