incomplete migration between fresh and salt water. The fish spawns and overwinters in fresh waters but feeds in large, brackish estuarine areas, the plumes of fresh water mixed with saline sea water that are rich in nutrients and important foraging areas. Such populations are known as winter races and often grow faster, mature at larger sizes, spawn earlier in spring and move further upstream than non-migratory stocks (spring races)
Dictionary of ichthyology. 2009.