A climate-driven schedule change
The arrival of flying fish in the Yellow Sea is a long-observed natural event, historically tied to the seasonal warming of the ocean. These fish, belonging to the family Exocoetidae, undertake seasonal migrations based on changes in sea surface temperature. One common species in the region is the Stained Flyingfish, Cheilopogon spilonotopterus. This species, and others like it, traditionally winter in the warmer southern waters of the Yellow Sea and the East China Sea. As spring progresses, they migrate north along the Korean Peninsula to coastal spawning grounds.
This migration is a classic example of phenology, the study of cyclic and seasonal natural phenomena. The timing is not random; it is a direct response to environmental cues. The optimal water temperature for many of these migrating species is between 13 and 15 degrees Celsius. These conditions occurred with predictable regularity, signaling the start of the spawning season, which typically runs from May to June in the coastal areas of the Korean Peninsula. This schedule is changing. The Yellow Sea's winter surface temperatures have risen significantly, by nearly 2 degrees Celsius between 1958 and 2014, a rate much faster than the global average. This accelerated warming is altering the timing of the annual migration, causing the fish to arrive progressively earlier.