Some organisms live out their entire existence within the estuary, while others begin life here and move elsewhere. Still others move to and from estuaries for various reasons, or migrate through them bound for fresh or salt water. One of the estuary's most important roles is that of nurserya vital rearing area for many species of fish and shellfish. It's estimated that 65 percent of America's commercial food fishes and shellfishes and nearly all inshore and near-shore saltwater sport fishes are vitally linked to the estuarine environment. A number of popular food and sport fishessurf smelt, jacksmelt, herring, and some races of chum and pink salmonspawn in or near the estuaries where their hatchlings grow to fingerlings or young adults before venturing out to sea.
Some species remain in or near the estuaries all their lives.
Several of the surfperches regularly visit Pacific estuaries to feed and to bear live young there. A few are permanent estuarine residents. All of the anadromous fishes, those that spend most of their lives in salt water but reproduce in fresh water, use the estuaries. Similarly, the catadromous speciesthose that mainly live in fresh water but spawn in salt watermigrate through the estuaries and may reside there as juveniles. Among the most important anadromous fishes are Atlantic and Pacific salmon, steelhead trout, striped bass, and American shad.