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Read MoreThe Penobscot River Restoration Project in part seeks to restore native fish runs of both anadromous and catadromous fish (for additional articles and updates on Penobscot fisheries, visit our River Culture and Wildlife pages).

Anadromous Fish are those species that spend the majority of their lives at sea but return to freshwater rivers, streams, and/or lakes to spawn.

There are ten anadromous fish species native to the state of Maine: alewife, striped bass, Atlantic salmon, rainbow smelt, blueback herring, American shad, sea lamprey, Atlantic sturgeon, shortnose sturgeon, and brook trout.

The spawning migration of each species of anadromous fish varies, but generally occurs in May and June when fish ascend rivers to spawn in rivers and/or lakes and ponds. Although some adults die after spawning, the majority of adults make their way downstream to the sea shortly after spawning. The young spend the summer in the lake or river environment while preparing to migrate. Juvenile fish begin moving to the sea from mid- July through October but some stay in fresh water longer. Following a period of three to five years (the majority are at sea for four years), they return to the freshwater environments where they were hatched.

Catadromous Fish spawn in the ocean and migrate to fresh water to grow to adult size.

Life Cycle of Catadromous Fish

Catadromous fish spawn in the ocean and migrate to fresh water to grow to adult size. The American eel has such a life cycle. As adult eels mature, they leave the brackish/freshwater growing areas in the fall (August to November), migrate to the Sargasso Sea and spawn during the winter. The Sargasso Sea is a large area of the western North Atlantic located east of the Bahamas and south of Bermuda. After spawning the adult eel dies. The eggs hatch after several days and develop into a larval stage which drifts through the ocean for several months until they enter the Gulf Stream current to be carried north towards the North American continent. As the larvae approach the continental shelf, the larvae transform into miniature transparent eels called "glass eels". As glass eels leave the open ocean and enter into estuaries they are known as elvers. With each life stage of the eel there is a commercial fishery which impacts not only eel populations but other species including salmon, alewives, smelt and trout. This migration begins in late winter and continues through the summer months. Eels may stay in growing areas from 8-25 years before migrating back to sea to spawn.

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