Of these fish species, only 32 species are year-round residents of the Bay. The remaining species enter the Bay either from freshwater streams or the Atlantic Ocean to feed, reproduce and find shelter. Resident fish tend to be smaller than migratory species and often occur in shallow waters, where they feed on a variety of invertebrates. The resident Bay anchovy, for example, is the most abundant fish in Bay waters and consequently forms a critical link in the food web because it serves as the dietary basis for many other species, including some species of birds and mammals. In winter it remains in the deep waters of the Bay, but in the warmer seasons it clings to shoreline areas, swimming in schools and feeding on zooplankton.
Catadromous fish live in freshwater, but travel to the high-salinity ocean waters to spawn.
The only catadromous species in the Bay ecosystem is the American eel , or Anguilla rostrata, which leaves its habitat in the Bay to spawn in the Sargasso Sea. Anadromous fish, such as the American shad and the blueback herring, travel from the high salinity waters of the lower Bay or Atlantic Ocean to spawn in the Bay watershed's freshwater rivers and streams. Other anadromous fish travel shorter distances to spawn and occupy a narrower range of salinities. For example, white perch journey from the middle Bay, which is not as salty as the ocean, to freshwater areas of the upper Bay and tributaries to spawn. The Chesapeake Bay and its tributaries sustain a wide diversity of species and have for centuries provided rich fishing grounds for commercial and recreational fisherman.