In an extreme example of the principle of natural selection, only the strongest could survive the journey home, thus maintaining the durability and health of the whole species. However, when the ice receded, many brook masu salmon were left stranded, unable to return to the sea. They had no choice but to become "landlocked" salmon.
這種自然界強烈的選種方式，讓優秀、強壯的鮭魚才能回到家，維持族群的優越，但冰河退去，許多櫻花鉤吻鮭無法再回到大海，不得已成了「陸封性」鮭魚。